Prof. Dr. Gregor Koblmüller
Academic Research Focus
- Innovative semiconductor quantum nanomaterials (III-V based nanowires, quantum dots and 2D heterostructures)
- Synthesis, simulation & characterization of electronic, optical and structural properties, as well as to device fabrication & probing device functionalities
- Development of unique nanothermoelectric materials and advanced-concept 3D-structured solar cells
monolithically integrated nanolasers and quantum light sources
Fields of Application
Microelectronics, Photonics, Semiconductor Materials, Solar Cells / Photovoltaics
Publications
24.
H Esmaielpour, P Schmiedeke, N Isaev, C Doganlar, M Döblinger, J J Finley, G Koblmüller
Hot carrier dynamics in III–V semiconductor nanowires under dominant radiative and Auger recombination Journal Article
In: Applied Physics Letters, vol. 126, no. 8, pp. 083505, 2025, ISSN: 0003-6951.
@article{nokey,
title = {Hot carrier dynamics in III\textendashV semiconductor nanowires under dominant radiative and Auger recombination},
author = {H Esmaielpour and P Schmiedeke and N Isaev and C Doganlar and M D\"{o}blinger and J J Finley and G Koblm\"{u}ller},
url = {https://doi.org/10.1063/5.0248247},
doi = {10.1063/5.0248247},
issn = {0003-6951},
year = {2025},
date = {2025-02-24},
journal = {Applied Physics Letters},
volume = {126},
number = {8},
pages = {083505},
abstract = {One-dimensional structures such as nanowires (NWs) show great promise in tailoring the rates of hot carrier thermalization in semiconductors with important implications for the design of efficient hot carrier absorbers. However, the fabrication of defect-free crystal structures and control of their intrinsic electronic properties can be challenging, raising concerns about the role of competing radiative and non-radiative recombination mechanisms that govern hot carrier effects. Here, we elucidate the impact of crystal purity and altered electronic properties on the hot carrier properties by comparing two classes of III\textendashV semiconductor NW arrays with similar bandgap energies and geometries, yet different crystal quality: one composed of GaAsSb NWs, which host antisite point defects but are free of planar stacking defects, and the other InGaAs NWs with a very high density of stacking defects. Photoluminescence spectroscopy demonstrates distinct hot carrier effects in both NW arrays; however, the InGaAs NWs exhibit stronger hot carrier effects, as evidenced by increased carrier temperature under identical photo-absorptivity. This difference arises from higher rates of Auger recombination in the InGaAs NWs due to their increased n-type conductivity, as confirmed by excitation power-dependent measurements. Our findings suggest that while enhancing material properties is crucial for improving the performance of hot carrier absorbers, optimizing conditions to increase the rates of Auger recombination will further boost the efficiency of these devices.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
One-dimensional structures such as nanowires (NWs) show great promise in tailoring the rates of hot carrier thermalization in semiconductors with important implications for the design of efficient hot carrier absorbers. However, the fabrication of defect-free crystal structures and control of their intrinsic electronic properties can be challenging, raising concerns about the role of competing radiative and non-radiative recombination mechanisms that govern hot carrier effects. Here, we elucidate the impact of crystal purity and altered electronic properties on the hot carrier properties by comparing two classes of III–V semiconductor NW arrays with similar bandgap energies and geometries, yet different crystal quality: one composed of GaAsSb NWs, which host antisite point defects but are free of planar stacking defects, and the other InGaAs NWs with a very high density of stacking defects. Photoluminescence spectroscopy demonstrates distinct hot carrier effects in both NW arrays; however, the InGaAs NWs exhibit stronger hot carrier effects, as evidenced by increased carrier temperature under identical photo-absorptivity. This difference arises from higher rates of Auger recombination in the InGaAs NWs due to their increased n-type conductivity, as confirmed by excitation power-dependent measurements. Our findings suggest that while enhancing material properties is crucial for improving the performance of hot carrier absorbers, optimizing conditions to increase the rates of Auger recombination will further boost the efficiency of these devices.
23.
H Esmaielpour, N Isaev, J Finley, G Koblmüller
Enhancement of hot carrier effects in core-shell InGaAs nanowires by Auger heating Proceedings Article
In: 2025 Conference on Physics Simulation and Photonic Engineering of Photovoltaic Devices, 2025, ISBN: 978-1-5106-8470-6, 978-1-5106-8471-3, (Times Cited: 0 Cited Reference Count: 0 Esmaielpour, H. Isaev, N. Finley, J. Koblmueller, G. Isaev, Nikita/HMV-0383-2023 0277-786x 1336104).
@inproceedings{nokey,
title = {Enhancement of hot carrier effects in core-shell InGaAs nanowires by Auger heating},
author = {H Esmaielpour and N Isaev and J Finley and G Koblm\"{u}ller},
url = {\<Go to ISI\>://WOS:001515820100003},
doi = {10.1117/12.3043850},
isbn = {978-1-5106-8470-6, 978-1-5106-8471-3},
year = {2025},
date = {2025-01-01},
booktitle = {2025 Conference on Physics Simulation and Photonic Engineering of Photovoltaic Devices},
volume = {13361},
series = {Proceedings of SPIE},
abstract = {Hot carrier solar cells are a category of third-generation photovoltaic devices focused on enhancing solar technology efficiency beyond the theoretical limits of single-junction devices. A crucial aspect of designing effective hot carrier solar cells is minimizing the rates of hot carrier thermalization within the solar cell absorbers. Nanowires (NWs) present promising opportunities for hot carrier solar cells due to their one-dimensional structure and favorable density-of-states characteristics. This study examines the hot carrier effects in core-shell InGaAs/InAlAs nanowires with diameters ranging from 110 nm to 200 nm. The findings from photoluminescence spectroscopy indicate a significant relationship between hot carrier effects and nanowire diameter. Specifically, as the diameter decreases from 200 nm to 160 nm, the hot carrier effects become more pronounced. However, further reduction in diameter, particularly below 160 nm, results in diminished hot carrier effects. The observed increase in hot carrier effects as the diameter decreases (between 160 nm and 200 nm) is attributed to the combined influences of phonon bottleneck and Auger heating mechanisms. Conversely, in the thinner nanowires, an increase in microstructural disorder contributes to higher rates of hot carrier thermalization, leading to reduced hot carrier effects. These results are consistent with existing theoretical models and previous experimental studies, including those employing time-resolved photoluminescence spectroscopy and high-resolution transmission electron microscopy.},
note = {Times Cited: 0
Cited Reference Count: 0
Esmaielpour, H. Isaev, N. Finley, J. Koblmueller, G.
Isaev, Nikita/HMV-0383-2023
0277-786x
1336104},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
Hot carrier solar cells are a category of third-generation photovoltaic devices focused on enhancing solar technology efficiency beyond the theoretical limits of single-junction devices. A crucial aspect of designing effective hot carrier solar cells is minimizing the rates of hot carrier thermalization within the solar cell absorbers. Nanowires (NWs) present promising opportunities for hot carrier solar cells due to their one-dimensional structure and favorable density-of-states characteristics. This study examines the hot carrier effects in core-shell InGaAs/InAlAs nanowires with diameters ranging from 110 nm to 200 nm. The findings from photoluminescence spectroscopy indicate a significant relationship between hot carrier effects and nanowire diameter. Specifically, as the diameter decreases from 200 nm to 160 nm, the hot carrier effects become more pronounced. However, further reduction in diameter, particularly below 160 nm, results in diminished hot carrier effects. The observed increase in hot carrier effects as the diameter decreases (between 160 nm and 200 nm) is attributed to the combined influences of phonon bottleneck and Auger heating mechanisms. Conversely, in the thinner nanowires, an increase in microstructural disorder contributes to higher rates of hot carrier thermalization, leading to reduced hot carrier effects. These results are consistent with existing theoretical models and previous experimental studies, including those employing time-resolved photoluminescence spectroscopy and high-resolution transmission electron microscopy.
22.
H Esmaielpour, P Schmiedeke, N Isaev, C Doganlar, M Döblinger, J J Finley, G Koblmüller
Competing mechanisms of dominant radiative and Auger recombination in hot carrier generation in III-V semiconductor nanowires Journal Article
In: arXiv preprint arXiv:2411.07822, 2024.
@article{nokey,
title = {Competing mechanisms of dominant radiative and Auger recombination in hot carrier generation in III-V semiconductor nanowires},
author = {H Esmaielpour and P Schmiedeke and N Isaev and C Doganlar and M D\"{o}blinger and J J Finley and G Koblm\"{u}ller},
year = {2024},
date = {2024-11-12},
journal = {arXiv preprint arXiv:2411.07822},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
21.
I Makhfudz, H Esmaielpour, Y Hajati, G Koblmüller, N Cavassilas
Interplay of electron trapping by defect midgap state and quantum confinement to optimize the hot-carrier effect in a nanowire structure Journal Article
In: Physical Review B, vol. 110, no. 12, pp. L121302, 2024.
@article{nokey,
title = {Interplay of electron trapping by defect midgap state and quantum confinement to optimize the hot-carrier effect in a nanowire structure},
author = {I Makhfudz and H Esmaielpour and Y Hajati and G Koblm\"{u}ller and N Cavassilas},
url = {https://link.aps.org/doi/10.1103/PhysRevB.110.L121302},
doi = {10.1103/PhysRevB.110.L121302},
year = {2024},
date = {2024-09-25},
journal = {Physical Review B},
volume = {110},
number = {12},
pages = {L121302},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
20.
T Schreitmüller, D Kumar Saluja, C E Mead, M Ramsteiner, H W Jeong, H Esmaielpour, C Huang, D Ruhstorfer, J J Finley, L J Lauhon, G Koblmüller
Spatial dependence of dopant incorporation and electrical transport in Si-doped GaAs(Sb) nanowires Journal Article
In: Physical Review Materials, vol. 8, no. 7, pp. 076002, 2024.
@article{nokey,
title = {Spatial dependence of dopant incorporation and electrical transport in Si-doped GaAs(Sb) nanowires},
author = {T Schreitm\"{u}ller and D Kumar Saluja and C E Mead and M Ramsteiner and H W Jeong and H Esmaielpour and C Huang and D Ruhstorfer and J J Finley and L J Lauhon and G Koblm\"{u}ller},
url = {https://link.aps.org/doi/10.1103/PhysRevMaterials.8.076002},
doi = {10.1103/PhysRevMaterials.8.076002},
year = {2024},
date = {2024-07-15},
journal = {Physical Review Materials},
volume = {8},
number = {7},
pages = {076002},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
19.
H Esmaielpour, N Isaev, J J Finley, G Koblmüller
Influence of Auger heating and Shockley-Read-Hall recombination on hot-carrier dynamics in InGaAs nanowires Journal Article
In: Physical Review B, vol. 109, no. 23, pp. 235303, 2024.
@article{nokey,
title = {Influence of Auger heating and Shockley-Read-Hall recombination on hot-carrier dynamics in InGaAs nanowires},
author = {H Esmaielpour and N Isaev and J J Finley and G Koblm\"{u}ller},
url = {https://link.aps.org/doi/10.1103/PhysRevB.109.235303},
doi = {10.1103/PhysRevB.109.235303},
year = {2024},
date = {2024-06-20},
journal = {Physical Review B},
volume = {109},
number = {23},
pages = {235303},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
18.
P Schmiedeke, C Doganlar, H W Jeong, M Döblinger, J J Finley, G Koblmüller
Low-threshold single ternary GaAsSb nanowire lasers emitting at silicon transparent wavelengths Journal Article
In: Applied Physics Letters, vol. 124, no. 7, pp. 071112, 2024, ISSN: 0003-6951.
@article{nokey,
title = {Low-threshold single ternary GaAsSb nanowire lasers emitting at silicon transparent wavelengths},
author = {P Schmiedeke and C Doganlar and H W Jeong and M D\"{o}blinger and J J Finley and G Koblm\"{u}ller},
url = {https://doi.org/10.1063/5.0191070},
doi = {10.1063/5.0191070},
issn = {0003-6951},
year = {2024},
date = {2024-02-12},
journal = {Applied Physics Letters},
volume = {124},
number = {7},
pages = {071112},
abstract = {Conventional binary III\textendashV nanowire (NW) lasers face substantial challenges in tuning their lasing emission to silicon transparent wavelengths and require complex quantum heterostructure designs for realizing on-chip integrated nanolasers. Here, an alternative and straightforward approach is reported by developing ternary III\textendashV NW-lasers in the form of surface-passivated GaAsSb NW-lasers grown on silicon. High-quality GaAsSb NW-cavities with high Sb-content (\>20%) and extended lengths (\>5 μm) are shown to exhibit striking radiative efficiency enhancements (∼200-fold) when passivated by closely lattice-matched InAlGaAs shell layers. Utilizing this core\textendashshell approach, optically pumped lasing is then demonstrated from single GaAsSb NW-lasers with lasing threshold as low as 3.2 μJ/cm2 at temperatures up to 250 K and emission wavelengths of ∼1.1\textendash1.2 μm. Analysis of the optical mode spectra and mode-dependent threshold gain further shows that lasing is induced by the fundamental HE11 modes, and likely even lower thresholds may be achieved by establishing the TE01 mode at increased NW-cavity diameters.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Conventional binary III–V nanowire (NW) lasers face substantial challenges in tuning their lasing emission to silicon transparent wavelengths and require complex quantum heterostructure designs for realizing on-chip integrated nanolasers. Here, an alternative and straightforward approach is reported by developing ternary III–V NW-lasers in the form of surface-passivated GaAsSb NW-lasers grown on silicon. High-quality GaAsSb NW-cavities with high Sb-content (>20%) and extended lengths (>5 μm) are shown to exhibit striking radiative efficiency enhancements (∼200-fold) when passivated by closely lattice-matched InAlGaAs shell layers. Utilizing this core–shell approach, optically pumped lasing is then demonstrated from single GaAsSb NW-lasers with lasing threshold as low as 3.2 μJ/cm2 at temperatures up to 250 K and emission wavelengths of ∼1.1–1.2 μm. Analysis of the optical mode spectra and mode-dependent threshold gain further shows that lasing is induced by the fundamental HE11 modes, and likely even lower thresholds may be achieved by establishing the TE01 mode at increased NW-cavity diameters.
17.
H Esmaielpour, N Isaev, I Makhfudz, M Döblinger, J J Finley, G Koblmüller
Strong Dimensional and Structural Dependencies of Hot Carrier Effects in InGaAs Nanowires: Implications for Photovoltaic Solar Cells Journal Article
In: ACS Applied Nano Materials, vol. 7, no. 3, pp. 2817-2824, 2024.
@article{nokey,
title = {Strong Dimensional and Structural Dependencies of Hot Carrier Effects in InGaAs Nanowires: Implications for Photovoltaic Solar Cells},
author = {H Esmaielpour and N Isaev and I Makhfudz and M D\"{o}blinger and J J Finley and G Koblm\"{u}ller},
url = {https://doi.org/10.1021/acsanm.3c05041},
doi = {10.1021/acsanm.3c05041},
year = {2024},
date = {2024-02-09},
journal = {ACS Applied Nano Materials},
volume = {7},
number = {3},
pages = {2817-2824},
abstract = {III\textendashV nanowire structures are among the promising material systems with applications in hot carrier solar cells. These nanostructures can meet the requirements for such photovoltaic devices, i.e., the suppression of thermalization loss, an efficient hot carrier transport, and enhanced photoabsorption thanks to their unique one-dimensional (1D) geometry and density-of-states. Here, we investigate the effects of spatial confinement of photogenerated hot carriers in InGaAs-InAlAs core\textendashshell nanowires, which presents an ideal class of hot carrier solar cell materials due to its suitable electronic properties. Using steady-state photoluminescence spectroscopy, our study reveals that by increasing the degree of spatial confinement and Auger recombination, the effects of hot carriers increase, which is in good agreement with theoretical modeling. However, for thin nanowires, the temperature of hot carriers decreases as the effects of crystal disorder increase. This observation is confirmed by probing the extent of the disorder-induced Urbach tail and linked to the presence of a higher density of stacking defects in the limit of thin nanowires. These findings expand our knowledge of hot carrier thermalization in nanowires, which can be applied for designing efficient 1D hot carrier absorbers for advanced-concept photovoltaic solar cells.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
III–V nanowire structures are among the promising material systems with applications in hot carrier solar cells. These nanostructures can meet the requirements for such photovoltaic devices, i.e., the suppression of thermalization loss, an efficient hot carrier transport, and enhanced photoabsorption thanks to their unique one-dimensional (1D) geometry and density-of-states. Here, we investigate the effects of spatial confinement of photogenerated hot carriers in InGaAs-InAlAs core–shell nanowires, which presents an ideal class of hot carrier solar cell materials due to its suitable electronic properties. Using steady-state photoluminescence spectroscopy, our study reveals that by increasing the degree of spatial confinement and Auger recombination, the effects of hot carriers increase, which is in good agreement with theoretical modeling. However, for thin nanowires, the temperature of hot carriers decreases as the effects of crystal disorder increase. This observation is confirmed by probing the extent of the disorder-induced Urbach tail and linked to the presence of a higher density of stacking defects in the limit of thin nanowires. These findings expand our knowledge of hot carrier thermalization in nanowires, which can be applied for designing efficient 1D hot carrier absorbers for advanced-concept photovoltaic solar cells.
16.
H W Jeong, A Ajay, M Döblinger, S Sturm, M Gómez Ruiz, R Zell, N Mukhundhan, D Stelzner, J Lähnemann, K Müller-Caspary, J J Finley, G Koblmüller
Axial Growth Characteristics of Optically Active InGaAs Nanowire Heterostructures for Integrated Nanophotonic Devices Journal Article
In: ACS Applied Nano Materials, vol. 7, no. 3, pp. 3032-3041, 2024.
@article{nokey,
title = {Axial Growth Characteristics of Optically Active InGaAs Nanowire Heterostructures for Integrated Nanophotonic Devices},
author = {H W Jeong and A Ajay and M D\"{o}blinger and S Sturm and M G\'{o}mez Ruiz and R Zell and N Mukhundhan and D Stelzner and J L\"{a}hnemann and K M\"{u}ller-Caspary and J J Finley and G Koblm\"{u}ller},
url = {https://doi.org/10.1021/acsanm.3c05392},
doi = {10.1021/acsanm.3c05392},
year = {2024},
date = {2024-01-24},
journal = {ACS Applied Nano Materials},
volume = {7},
number = {3},
pages = {3032-3041},
abstract = {III\textendashV semiconductor nanowire (NW) heterostructures with axial InGaAs active regions hold large potential for diverse on-chip device applications, including site-selectively integrated quantum light sources, NW lasers with high material gain, as well as resonant tunneling diodes and avalanche photodiodes. Despite various promising efforts toward high-quality single or multiple axial InGaAs heterostacks using noncatalytic growth mechanisms, the important roles of facet-dependent shape evolution, crystal defects, and the applicability to more universal growth schemes have remained elusive. Here, we report the growth of optically active InGaAs axial NW heterostructures via completely catalyst-free, selective-area molecular beam epitaxy directly on silicon (Si) using GaAs(Sb) NW arrays as tunable, high-uniformity growth templates and highlight fundamental relationships between structural, morphological, and optical properties of the InGaAs region. Structural, compositional, and 3D-tomographic characterizations affirm the desired directional growth along the NW axis with no radial growth observed. Clearly distinct luminescence from the InGaAs active region is demonstrated, where tunable array\textendashgeometry parameters and In content up to 20% are further investigated. Based on the underlying twin-induced growth mode, we further describe the facet-dependent shape and interface evolution of the InGaAs segment and its direct correlation with emission energy.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
III–V semiconductor nanowire (NW) heterostructures with axial InGaAs active regions hold large potential for diverse on-chip device applications, including site-selectively integrated quantum light sources, NW lasers with high material gain, as well as resonant tunneling diodes and avalanche photodiodes. Despite various promising efforts toward high-quality single or multiple axial InGaAs heterostacks using noncatalytic growth mechanisms, the important roles of facet-dependent shape evolution, crystal defects, and the applicability to more universal growth schemes have remained elusive. Here, we report the growth of optically active InGaAs axial NW heterostructures via completely catalyst-free, selective-area molecular beam epitaxy directly on silicon (Si) using GaAs(Sb) NW arrays as tunable, high-uniformity growth templates and highlight fundamental relationships between structural, morphological, and optical properties of the InGaAs region. Structural, compositional, and 3D-tomographic characterizations affirm the desired directional growth along the NW axis with no radial growth observed. Clearly distinct luminescence from the InGaAs active region is demonstrated, where tunable array–geometry parameters and In content up to 20% are further investigated. Based on the underlying twin-induced growth mode, we further describe the facet-dependent shape and interface evolution of the InGaAs segment and its direct correlation with emission energy.
15.
T Schreitmüller, H W Jeong, H Esmaielpour, C E Mead, M Ramsteiner, P Schmiedeke, A Thurn, A Ajay, S Matich, M Döblinger, L J Lauhon, J J Finley, G Koblmüller
Large Tolerance of Lasing Properties to Impurity Defects in GaAs(Sb)-AlGaAs Core-Shell Nanowire Lasers Journal Article
In: Advanced Functional Materials, vol. n/a, no. n/a, pp. 2311210, 2023, ISSN: 1616-301X.
@article{nokey,
title = {Large Tolerance of Lasing Properties to Impurity Defects in GaAs(Sb)-AlGaAs Core-Shell Nanowire Lasers},
author = {T Schreitm\"{u}ller and H W Jeong and H Esmaielpour and C E Mead and M Ramsteiner and P Schmiedeke and A Thurn and A Ajay and S Matich and M D\"{o}blinger and L J Lauhon and J J Finley and G Koblm\"{u}ller},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.202311210},
doi = {https://doi.org/10.1002/adfm.202311210},
issn = {1616-301X},
year = {2023},
date = {2023-12-08},
journal = {Advanced Functional Materials},
volume = {n/a},
number = {n/a},
pages = {2311210},
abstract = {Abstract GaAs-AlGaAs based nanowire (NW) lasers hold great potential for on-chip photonic applications, where lasing metrics have steadily improved over the years by optimizing resonator design and surface passivation methods. The factor that will ultimately limit the performance will depend on material properties, such as native- or impurity-induced point defects and their impact on non-radiative recombination. Here, the role of impurity-induced point defects on the lasing performance of low-threshold GaAs(Sb)-AlGaAs NW-lasers is evaluated, particularly by exploring Si-dopants and their associated vacancy complexes. Si-induced point defects and their self-compensating nature are identified using correlated atom probe tomography, resonant Raman scattering, and photoluminescence experiments. Under pulsed optical excitation the lasing threshold is remarkably low (\<10 µJ cm−2) and insensitive to impurity defects over a wide range of Si doping densities, while excess doping ([Si]\>1019 cm−3) imposes increased threshold at low temperature. These characteristics coincide with increased Shockley-Read-Hall recombination, reflected by shorter carrier lifetimes, and reduced internal quantum efficiencies (IQE) . Remarkably, despite the lower IQE the presence of self-compensating Si-vacancy defects provides an improved temperature stability in lasing threshold with higher characteristic temperature and room-temperature lasing. These findings highlight an overall large tolerance of lasing metrics to impurity defects in GaAs-AlGaAs based NW-lasers.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract GaAs-AlGaAs based nanowire (NW) lasers hold great potential for on-chip photonic applications, where lasing metrics have steadily improved over the years by optimizing resonator design and surface passivation methods. The factor that will ultimately limit the performance will depend on material properties, such as native- or impurity-induced point defects and their impact on non-radiative recombination. Here, the role of impurity-induced point defects on the lasing performance of low-threshold GaAs(Sb)-AlGaAs NW-lasers is evaluated, particularly by exploring Si-dopants and their associated vacancy complexes. Si-induced point defects and their self-compensating nature are identified using correlated atom probe tomography, resonant Raman scattering, and photoluminescence experiments. Under pulsed optical excitation the lasing threshold is remarkably low (<10 µJ cm−2) and insensitive to impurity defects over a wide range of Si doping densities, while excess doping ([Si]>1019 cm−3) imposes increased threshold at low temperature. These characteristics coincide with increased Shockley-Read-Hall recombination, reflected by shorter carrier lifetimes, and reduced internal quantum efficiencies (IQE) . Remarkably, despite the lower IQE the presence of self-compensating Si-vacancy defects provides an improved temperature stability in lasing threshold with higher characteristic temperature and room-temperature lasing. These findings highlight an overall large tolerance of lasing metrics to impurity defects in GaAs-AlGaAs based NW-lasers.
14.
D Sandner, H Esmaielpour, F D Giudice, S Meder, M Nuber, R Kienberger, G Koblmüller, H Iglev
Hot Electron Dynamics in InAs–AlAsSb Core–Shell Nanowires Journal Article
In: ACS Applied Energy Materials, vol. 6, no. 20, pp. 10467-10474, 2023.
@article{nokey,
title = {Hot Electron Dynamics in InAs\textendashAlAsSb Core\textendashShell Nanowires},
author = {D Sandner and H Esmaielpour and F D Giudice and S Meder and M Nuber and R Kienberger and G Koblm\"{u}ller and H Iglev},
url = {https://doi.org/10.1021/acsaem.3c01565},
doi = {10.1021/acsaem.3c01565},
year = {2023},
date = {2023-10-05},
journal = {ACS Applied Energy Materials},
volume = {6},
number = {20},
pages = {10467-10474},
abstract = {Semiconductor nanowires (NWs) have shown evidence of robust hot-carrier effects due to their small dimensions, making them attractive for advanced photoenergy conversion concepts. Especially, indium arsenide (InAs) NWs are promising candidates for harvesting hot carriers due to their high absorption coefficient, high carrier mobility, and large effective electron-to-hole mass difference. Here, we investigate the cooling and recombination dynamics of photoexcited hot carriers in pure and passivated InAs NWs by using ultrafast near-infrared pump\textendashprobe spectroscopy. We observe reduced Auger recombination in pure InAs NWs compared to that in passivated ones and associate this with charge-carrier separation by surface band bending. Similarly, faster carrier cooling by electron\textendashhole scattering is observed in passivated InAs\textendashAlAsSb NWs at high carrier densities in excess of 1018 cm\textendash3, where hot electron lifetimes in this regime increase substantially with the pump fluence due to Auger heating. These results emphasize the importance of type-II alignment for charge-carrier separation in hot-carrier devices to suppress carrier-mediated cooling channels. In addition, a separate charge-carrier population lasting up to several nanoseconds is observed for photoexcitation of the NW shell. Despite the high conduction band offset, carrier migration is not observed in the range of 40 ps to 2 ns. This observation may open avenues for core\textendashshell NW multijunction solar cells.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Semiconductor nanowires (NWs) have shown evidence of robust hot-carrier effects due to their small dimensions, making them attractive for advanced photoenergy conversion concepts. Especially, indium arsenide (InAs) NWs are promising candidates for harvesting hot carriers due to their high absorption coefficient, high carrier mobility, and large effective electron-to-hole mass difference. Here, we investigate the cooling and recombination dynamics of photoexcited hot carriers in pure and passivated InAs NWs by using ultrafast near-infrared pump–probe spectroscopy. We observe reduced Auger recombination in pure InAs NWs compared to that in passivated ones and associate this with charge-carrier separation by surface band bending. Similarly, faster carrier cooling by electron–hole scattering is observed in passivated InAs–AlAsSb NWs at high carrier densities in excess of 1018 cm–3, where hot electron lifetimes in this regime increase substantially with the pump fluence due to Auger heating. These results emphasize the importance of type-II alignment for charge-carrier separation in hot-carrier devices to suppress carrier-mediated cooling channels. In addition, a separate charge-carrier population lasting up to several nanoseconds is observed for photoexcitation of the NW shell. Despite the high conduction band offset, carrier migration is not observed in the range of 40 ps to 2 ns. This observation may open avenues for core–shell NW multijunction solar cells.
13.
P Schmiedeke, F Panciera, J-C Harmand, L Travers, G Koblmüller
Real-time thermal decomposition kinetics of GaAs nanowires and their crystal polytypes on the atomic scale Journal Article
In: Nanoscale Advances, vol. 5, no. 11, pp. 2994-3004, 2023.
@article{nokey,
title = {Real-time thermal decomposition kinetics of GaAs nanowires and their crystal polytypes on the atomic scale},
author = {P Schmiedeke and F Panciera and J-C Harmand and L Travers and G Koblm\"{u}ller},
url = {http://dx.doi.org/10.1039/D3NA00135K},
doi = {10.1039/D3NA00135K},
year = {2023},
date = {2023-05-05},
journal = {Nanoscale Advances},
volume = {5},
number = {11},
pages = {2994-3004},
abstract = {Nanowires (NWs) offer unique opportunities for tuning the properties of III\textendashV semiconductors by simultaneously controlling their nanoscale dimensions and switching their crystal phase between zinc-blende (ZB) and wurtzite (WZ). While much of this control has been enabled by direct, forward growth, the reverse reaction, i.e., crystal decomposition, provides very powerful means to further tailor properties towards the ultra-scaled dimensional level. Here, we use in situ transmission electron microscopy (TEM) to investigate the thermal decomposition kinetics of clean, ultrathin GaAs NWs and the role of distinctly different crystal polytypes in real-time and on the atomic scale. The whole process, from the NW growth to the decomposition, is conducted in situ without breaking vacuum to maintain pristine crystal surfaces. Radial decomposition occurs much faster for ZB- compared to WZ-phase NWs, due to the development of nano-faceted sidewall morphology and sublimation along the entire NW length. In contrast, WZ NWs form single-faceted, vertical sidewalls with decomposition proceeding only via step-flow mechanism from the NW tip. Concurrent axial decomposition is generally faster than the radial process, but is significantly faster (∼4-fold) in WZ phase, due to the absence of well-defined facets at the tip of WZ NWs. The results further show quantitatively the influence of the NW diameter on the sublimation and step-flow decomposition velocities elucidating several effects that can be exploited to fine-tune the NW dimensions.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Nanowires (NWs) offer unique opportunities for tuning the properties of III–V semiconductors by simultaneously controlling their nanoscale dimensions and switching their crystal phase between zinc-blende (ZB) and wurtzite (WZ). While much of this control has been enabled by direct, forward growth, the reverse reaction, i.e., crystal decomposition, provides very powerful means to further tailor properties towards the ultra-scaled dimensional level. Here, we use in situ transmission electron microscopy (TEM) to investigate the thermal decomposition kinetics of clean, ultrathin GaAs NWs and the role of distinctly different crystal polytypes in real-time and on the atomic scale. The whole process, from the NW growth to the decomposition, is conducted in situ without breaking vacuum to maintain pristine crystal surfaces. Radial decomposition occurs much faster for ZB- compared to WZ-phase NWs, due to the development of nano-faceted sidewall morphology and sublimation along the entire NW length. In contrast, WZ NWs form single-faceted, vertical sidewalls with decomposition proceeding only via step-flow mechanism from the NW tip. Concurrent axial decomposition is generally faster than the radial process, but is significantly faster (∼4-fold) in WZ phase, due to the absence of well-defined facets at the tip of WZ NWs. The results further show quantitatively the influence of the NW diameter on the sublimation and step-flow decomposition velocities elucidating several effects that can be exploited to fine-tune the NW dimensions.
12.
M O Hill, P Schmiedeke, C Huang, S Maddali, X Hu, S O Hruszkewycz, J J Finley, G Koblmüller, L J Lauhon
3D Bragg Coherent Diffraction Imaging of Extended Nanowires: Defect Formation in Highly Strained InGaAs Quantum Wells Journal Article
In: ACS Nano, vol. 16, no. 12, pp. 20281-20293, 2022, ISSN: 1936-0851.
@article{nokey,
title = {3D Bragg Coherent Diffraction Imaging of Extended Nanowires: Defect Formation in Highly Strained InGaAs Quantum Wells},
author = {M O Hill and P Schmiedeke and C Huang and S Maddali and X Hu and S O Hruszkewycz and J J Finley and G Koblm\"{u}ller and L J Lauhon},
url = {https://doi.org/10.1021/acsnano.2c06071},
doi = {10.1021/acsnano.2c06071},
issn = {1936-0851},
year = {2022},
date = {2022-12-27},
journal = {ACS Nano},
volume = {16},
number = {12},
pages = {20281-20293},
abstract = {InGaAs quantum wells embedded in GaAs nanowires can serve as compact near-infrared emitters for direct integration onto Si complementary metal oxide semiconductor technology. While the core\textendashshell geometry in principle allows for a greater tuning of composition and emission, especially farther into the infrared, the practical limits of elastic strain accommodation in quantum wells on multifaceted nanowires have not been established. One barrier to progress is the difficulty of directly comparing the emission characteristics and the precise microstructure of a single nanowire. Here we report an approach to correlating quantum well morphology, strain, defects, and emission to understand the limits of elastic strain accommodation in nanowire quantum wells specific to their geometry. We realize full 3D Bragg coherent diffraction imaging (BCDI) of intact quantum wells on vertically oriented epitaxial nanowires, which enables direct correlation with single-nanowire photoluminescence. By growing In0.2Ga0.8As quantum wells of distinct thicknesses on different facets of the same nanowire, we identified the critical thickness at which defects are nucleated. A correlation with a traditional transmission electron microscopy analysis confirms that BCDI can image the extended structure of defects. Finite element simulations of electron and hole states explain the emission characteristics arising from strained and partially relaxed regions. This approach, imaging the 3D strain and microstructure of intact nanowire core\textendashshell structures with application-relevant dimensions, can aid the development of predictive models that enable the design of new compact infrared emitters.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
InGaAs quantum wells embedded in GaAs nanowires can serve as compact near-infrared emitters for direct integration onto Si complementary metal oxide semiconductor technology. While the core–shell geometry in principle allows for a greater tuning of composition and emission, especially farther into the infrared, the practical limits of elastic strain accommodation in quantum wells on multifaceted nanowires have not been established. One barrier to progress is the difficulty of directly comparing the emission characteristics and the precise microstructure of a single nanowire. Here we report an approach to correlating quantum well morphology, strain, defects, and emission to understand the limits of elastic strain accommodation in nanowire quantum wells specific to their geometry. We realize full 3D Bragg coherent diffraction imaging (BCDI) of intact quantum wells on vertically oriented epitaxial nanowires, which enables direct correlation with single-nanowire photoluminescence. By growing In0.2Ga0.8As quantum wells of distinct thicknesses on different facets of the same nanowire, we identified the critical thickness at which defects are nucleated. A correlation with a traditional transmission electron microscopy analysis confirms that BCDI can image the extended structure of defects. Finite element simulations of electron and hole states explain the emission characteristics arising from strained and partially relaxed regions. This approach, imaging the 3D strain and microstructure of intact nanowire core–shell structures with application-relevant dimensions, can aid the development of predictive models that enable the design of new compact infrared emitters.
11.
D Sandner, H Esmaielpour, F Del Giudice, M Nuber, R Kienberger, G Koblmüller, H Iglev
Hot Carrier Dynamics in InAs-AlAsSb Core-Shell Nanowires Journal Article
In: arXiv preprint arXiv:2210.11886, 2022.
@article{nokey,
title = {Hot Carrier Dynamics in InAs-AlAsSb Core-Shell Nanowires},
author = {D Sandner and H Esmaielpour and F Del Giudice and M Nuber and R Kienberger and G Koblm\"{u}ller and H Iglev},
url = {https://arxiv.org/abs/2210.11886},
doi = {https://doi.org/10.48550/arXiv.2210.11886},
year = {2022},
date = {2022-10-25},
journal = {arXiv preprint arXiv:2210.11886},
abstract = {Semiconductor nanowires (NWs) have shown evidence of robust hot carrier effects due to their small dimensions. The relaxation dynamics of hot carriers in these nanostructures, generated by photo-absorption, are of great importance in optoelectronic devices and high efficiency solar cells, such as hot carrier solar cells. Among various III-V semiconductors, indium arsenide (InAs) NWs are promising candidates for their applications in advanced light harvesting devices due to their high photo-absorptivity and high mobility. Here, we investigate the hot carrier dynamics in InAs-AlAsSb core-shell NWs, as well as bare-core InAs NWs, using ultrafast pump-probe spectroscopy with widely tuned pump and probe energies. We have found a lifetime of 2.3 ps for longitudinal optical (LO) phonons and hot electron lifetimes of about 3 ps and 30 ps for carrier-carrier interactions and electron-phonon interactions, respectively. In addition, we have investigated the electronic states in the AlAsSb-shell and found that, despite the large band offset of the core-shell design in the conduction band, excited carriers remain in the shell longer than 100 ps. Our results indicate evidence of plasmon-tailored core-shell NWs for efficient light harvesting devices, which could open potential avenues for improving the efficiency of photovoltaic solar cells.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Semiconductor nanowires (NWs) have shown evidence of robust hot carrier effects due to their small dimensions. The relaxation dynamics of hot carriers in these nanostructures, generated by photo-absorption, are of great importance in optoelectronic devices and high efficiency solar cells, such as hot carrier solar cells. Among various III-V semiconductors, indium arsenide (InAs) NWs are promising candidates for their applications in advanced light harvesting devices due to their high photo-absorptivity and high mobility. Here, we investigate the hot carrier dynamics in InAs-AlAsSb core-shell NWs, as well as bare-core InAs NWs, using ultrafast pump-probe spectroscopy with widely tuned pump and probe energies. We have found a lifetime of 2.3 ps for longitudinal optical (LO) phonons and hot electron lifetimes of about 3 ps and 30 ps for carrier-carrier interactions and electron-phonon interactions, respectively. In addition, we have investigated the electronic states in the AlAsSb-shell and found that, despite the large band offset of the core-shell design in the conduction band, excited carriers remain in the shell longer than 100 ps. Our results indicate evidence of plasmon-tailored core-shell NWs for efficient light harvesting devices, which could open potential avenues for improving the efficiency of photovoltaic solar cells.
10.
D Ruhstorfer, M Döblinger, H Riedl, J J Finley, G Koblmüller
Role of twin defects on growth dynamics and size distribution of undoped and Si-doped GaAs nanowires by selective area epitaxy Journal Article
In: Journal of Applied Physics, vol. 132, no. 20, pp. 204302, 2022.
@article{nokey,
title = {Role of twin defects on growth dynamics and size distribution of undoped and Si-doped GaAs nanowires by selective area epitaxy},
author = {D Ruhstorfer and M D\"{o}blinger and H Riedl and J J Finley and G Koblm\"{u}ller},
url = {https://aip.scitation.org/doi/abs/10.1063/5.0124808},
doi = {10.1063/5.0124808},
year = {2022},
date = {2022-09-08},
journal = {Journal of Applied Physics},
volume = {132},
number = {20},
pages = {204302},
abstract = {We report the effects of Si doping on the growth dynamics and size distribution of entirely catalyst-free GaAs nanowire (NW) arrays grown by selective area molecular beam epitaxy on SiO2-masked Si (111) substrates. Surprising improvements in the NW-array uniformity are found with increasing Si doping, while the growth of undoped NWs appears in a metastable regime, evidenced by large size and shape distributions, and the simultaneous presence of crystallites with tetrahedral termination. Correlating scanning electron microscopy and transmission electron microscopy investigations, we propose that the size and shape distributions are strongly linked to the underlying twin defect formation probabilities that govern the growth. Under the present growth conditions, Si-doping of GaAs NWs leads to a very high twin defect formation probability (∼0.4), while undoped NWs exhibit a nearly threefold decreased probability (∼0.15). By adopting a model for facet-mediated growth, we describe how the altered twin formation probabilities impact the competing growth of the relevant low-index NW facets, and hence, NW size and shape. Our model is further supported by a generic Monte Carlo simulation approach to highlight the role of twin defects in reproducing the experimentally observed size distributions.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report the effects of Si doping on the growth dynamics and size distribution of entirely catalyst-free GaAs nanowire (NW) arrays grown by selective area molecular beam epitaxy on SiO2-masked Si (111) substrates. Surprising improvements in the NW-array uniformity are found with increasing Si doping, while the growth of undoped NWs appears in a metastable regime, evidenced by large size and shape distributions, and the simultaneous presence of crystallites with tetrahedral termination. Correlating scanning electron microscopy and transmission electron microscopy investigations, we propose that the size and shape distributions are strongly linked to the underlying twin defect formation probabilities that govern the growth. Under the present growth conditions, Si-doping of GaAs NWs leads to a very high twin defect formation probability (∼0.4), while undoped NWs exhibit a nearly threefold decreased probability (∼0.15). By adopting a model for facet-mediated growth, we describe how the altered twin formation probabilities impact the competing growth of the relevant low-index NW facets, and hence, NW size and shape. Our model is further supported by a generic Monte Carlo simulation approach to highlight the role of twin defects in reproducing the experimentally observed size distributions.
9.
F Del Giudice, S Fust, P Schmiedeke, J Pantle, M Döblinger, A Ajay, S Meder, H Riedl, J J Finley, G Koblmüller
Epitaxial type-I and type-II InAs-AlAsSb core–shell nanowires on silicon Journal Article
In: Applied Physics Letters, vol. 119, no. 19, pp. 193102, 2021, ISSN: 0003-6951.
@article{nokey,
title = {Epitaxial type-I and type-II InAs-AlAsSb core\textendashshell nanowires on silicon},
author = {F Del Giudice and S Fust and P Schmiedeke and J Pantle and M D\"{o}blinger and A Ajay and S Meder and H Riedl and J J Finley and G Koblm\"{u}ller},
url = {https://doi.org/10.1063/5.0065867},
doi = {10.1063/5.0065867},
issn = {0003-6951},
year = {2021},
date = {2021-11-08},
journal = {Applied Physics Letters},
volume = {119},
number = {19},
pages = {193102},
abstract = {Low-bandgap semiconductor nanowires (NWs) attract considerable interest for mid-infrared (MIR) photonics and optoelectronics, where ideal candidate materials require surface-passivated core\textendashshell systems with large tunability in band offset, lineup, and emission wavelength while maintaining close lattice-matching conditions. Here, we propose and demonstrate epitaxial InAs\textendashAlAsSb core\textendashshell NW arrays on silicon (Si) that offer exceptional control over both the internal strain close to lattice-matching as well as band lineups tunable between type-I and type-II, with almost no analogue in the III\textendashV materials family. We develop direct monolithic growth of high-uniformity InAs\textendashAlAsSb NWs with wide tunability in shell composition and employ correlated Raman scattering and micro-photoluminescence spectroscopy to elaborate the interplay among hydrostatic strain, band lineup, and emission energy of the NW core luminescence tuned from ∼0.4 to 0.55 eV. Electronic structure calculations further support the experimentally observed tunability between type-I and type-II band lineups. The Si-integrated InAs-AlAsSb NW materials system holds large prospects not only for on-chip MIR photonics but also for other applications including high-speed transistors and NW-based hot carrier solar cells.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Low-bandgap semiconductor nanowires (NWs) attract considerable interest for mid-infrared (MIR) photonics and optoelectronics, where ideal candidate materials require surface-passivated core–shell systems with large tunability in band offset, lineup, and emission wavelength while maintaining close lattice-matching conditions. Here, we propose and demonstrate epitaxial InAs–AlAsSb core–shell NW arrays on silicon (Si) that offer exceptional control over both the internal strain close to lattice-matching as well as band lineups tunable between type-I and type-II, with almost no analogue in the III–V materials family. We develop direct monolithic growth of high-uniformity InAs–AlAsSb NWs with wide tunability in shell composition and employ correlated Raman scattering and micro-photoluminescence spectroscopy to elaborate the interplay among hydrostatic strain, band lineup, and emission energy of the NW core luminescence tuned from ∼0.4 to 0.55 eV. Electronic structure calculations further support the experimentally observed tunability between type-I and type-II band lineups. The Si-integrated InAs-AlAsSb NW materials system holds large prospects not only for on-chip MIR photonics but also for other applications including high-speed transistors and NW-based hot carrier solar cells.
8.
A Thurn, J Bissinger, S Meinecke, P Schmiedeke, S S Oh, W W Chow, K Lüdge, G Koblmüller, J J Finley
Self-induced ultrafast electron-hole plasma temperature oscillations in nanowire lasers Journal Article
In: arXiv preprint arXiv:2108.11784, 2021.
@article{nokey,
title = {Self-induced ultrafast electron-hole plasma temperature oscillations in nanowire lasers},
author = {A Thurn and J Bissinger and S Meinecke and P Schmiedeke and S S Oh and W W Chow and K L\"{u}dge and G Koblm\"{u}ller and J J Finley},
url = {https://arxiv.org/abs/2108.11784},
doi = {arXiv:2108.11784v2},
year = {2021},
date = {2021-09-06},
journal = {arXiv preprint arXiv:2108.11784},
abstract = {Nanowire lasers can be monolithically and site-selectively integrated onto silicon photonic circuits. To assess their full potential for ultrafast opto-electronic devices, a detailed understanding of their lasing dynamics is crucial. However, the roles played by their resonator geometry and the microscopic processes that mediate energy exchange between the photonic, electronic, and phononic systems are largely unexplored. Here, we apply femtosecond pump-probe spectroscopy to show that GaAs-AlGaAs core-shell nanowire lasers exhibit sustained intensity oscillations with frequencies ranging from 160 GHz to 260 GHz. These dynamics are intricately linked to the strong interaction between the lasing mode and the gain material arising from their wavelength-scale dimensions. Combined with dynamic competition between photoinduced carrier heating and cooling via phonon scattering, this enables self-induced electron-hole plasma temperature oscillations, which modulate the laser output. We anticipate that our results will lead to new approaches for ultrafast intensity and phase modulation of chip-integrated nanoscale semiconductor lasers.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Nanowire lasers can be monolithically and site-selectively integrated onto silicon photonic circuits. To assess their full potential for ultrafast opto-electronic devices, a detailed understanding of their lasing dynamics is crucial. However, the roles played by their resonator geometry and the microscopic processes that mediate energy exchange between the photonic, electronic, and phononic systems are largely unexplored. Here, we apply femtosecond pump-probe spectroscopy to show that GaAs-AlGaAs core-shell nanowire lasers exhibit sustained intensity oscillations with frequencies ranging from 160 GHz to 260 GHz. These dynamics are intricately linked to the strong interaction between the lasing mode and the gain material arising from their wavelength-scale dimensions. Combined with dynamic competition between photoinduced carrier heating and cooling via phonon scattering, this enables self-induced electron-hole plasma temperature oscillations, which modulate the laser output. We anticipate that our results will lead to new approaches for ultrafast intensity and phase modulation of chip-integrated nanoscale semiconductor lasers.
7.
P Schmiedeke, A Thurn, S Matich, M Döblinger, J J Finley, G Koblmüller
Low-threshold strain-compensated InGaAs/(In,Al)GaAs multi-quantum well nanowire lasers emitting near 1.3 μm at room temperature Journal Article
In: Applied Physics Letters, vol. 118, no. 22, 2021, ISSN: 0003-6951.
@article{nokey,
title = {Low-threshold strain-compensated InGaAs/(In,Al)GaAs multi-quantum well nanowire lasers emitting near 1.3 μm at room temperature},
author = {P Schmiedeke and A Thurn and S Matich and M D\"{o}blinger and J J Finley and G Koblm\"{u}ller},
url = {https://doi.org/10.1063/5.0048807},
doi = {10.1063/5.0048807},
issn = {0003-6951},
year = {2021},
date = {2021-05-31},
journal = {Applied Physics Letters},
volume = {118},
number = {22},
abstract = {Realizing telecom-band lasing in GaAs-based nanowires (NW) with low bandgap gain media has proven to be notoriously difficult due to the high compressive strain built up in the active regions. Here, we demonstrate an advanced coaxial GaAs-InGaAs multi-quantum well (MQW) nanowire laser that solves previous limitations by the introduction of a strain compensating InAlGaAs buffer layer between the GaAs core and the MQW active region. Using a buffer layer thickness comparable to the core diameter applies a significant tensile strain to the GaAs core which efficiently minimizes the compressive strain in the InGaAs MQW and enables large In-content without plastic relaxation. Experimental verification is shown for NW-lasers with an In-content of up to 40% in the MQW, evidencing a clear strain-relieved redshift of the lasing emission and a strong reduction of the lasing threshold compared to highly strained MQWs in state-of-the-art GaAs NW-lasers. This way we achieve optically pumped room temperature lasing operation with a threshold below 50 μJ cm−2 in the telecom O-band close to 1.3 μm.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Realizing telecom-band lasing in GaAs-based nanowires (NW) with low bandgap gain media has proven to be notoriously difficult due to the high compressive strain built up in the active regions. Here, we demonstrate an advanced coaxial GaAs-InGaAs multi-quantum well (MQW) nanowire laser that solves previous limitations by the introduction of a strain compensating InAlGaAs buffer layer between the GaAs core and the MQW active region. Using a buffer layer thickness comparable to the core diameter applies a significant tensile strain to the GaAs core which efficiently minimizes the compressive strain in the InGaAs MQW and enables large In-content without plastic relaxation. Experimental verification is shown for NW-lasers with an In-content of up to 40% in the MQW, evidencing a clear strain-relieved redshift of the lasing emission and a strong reduction of the lasing threshold compared to highly strained MQWs in state-of-the-art GaAs NW-lasers. This way we achieve optically pumped room temperature lasing operation with a threshold below 50 μJ cm−2 in the telecom O-band close to 1.3 μm.
6.
D Ruhstorfer, A Lang, S Matich, M Döblinger, H Riedl, J J Finley, G Koblmüller
Growth dynamics and compositional structure in periodic InAsSb nanowire arrays on Si (111) grown by selective area molecular beam epitaxy Journal Article
In: Nanotechnology, vol. 32, no. 13, pp. 135604, 2021, ISSN: 0957-4484.
@article{,
title = {Growth dynamics and compositional structure in periodic InAsSb nanowire arrays on Si (111) grown by selective area molecular beam epitaxy},
author = {D Ruhstorfer and A Lang and S Matich and M D\"{o}blinger and H Riedl and J J Finley and G Koblm\"{u}ller},
issn = {0957-4484},
year = {2021},
date = {2021-01-08},
journal = {Nanotechnology},
volume = {32},
number = {13},
pages = {135604},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
5.
Del F Giudice, J Becker, De C Rose, M Döblinger, D Ruhstorfer, L Suomenniemi, J Treu, H Riedl, J J Finley, G Koblmüller
Ultrathin catalyst-free InAs nanowires on silicon with distinct 1D sub-band transport properties Journal Article
In: Nanoscale, vol. 12, no. 42, pp. 21857-21868, 2020, ISSN: 2040-3364.
@article{,
title = {Ultrathin catalyst-free InAs nanowires on silicon with distinct 1D sub-band transport properties},
author = {Del F Giudice and J Becker and De C Rose and M D\"{o}blinger and D Ruhstorfer and L Suomenniemi and J Treu and H Riedl and J J Finley and G Koblm\"{u}ller},
url = {http://dx.doi.org/10.1039/D0NR05666A},
doi = {10.1039/D0NR05666A},
issn = {2040-3364},
year = {2020},
date = {2020-10-01},
journal = {Nanoscale},
volume = {12},
number = {42},
pages = {21857-21868},
abstract = {Ultrathin InAs nanowires (NW) with a one-dimensional (1D) sub-band structure are promising materials for advanced quantum-electronic devices, where dimensions in the sub-30 nm diameter limit together with post-CMOS integration scenarios on Si are much desired. Here, we demonstrate two site-selective synthesis methods that achieve epitaxial, high aspect ratio InAs NWs on Si with ultrathin diameters below 20 nm. The first approach exploits direct vapor\textendashsolid growth to tune the NW diameter by interwire spacing, mask opening size and growth time. The second scheme explores a unique reverse-reaction growth by which the sidewalls of InAs NWs are thermally decomposed under controlled arsenic flux and annealing time. Interesting kinetically limited dependencies between interwire spacing and thinning dynamics are found, yielding diameters as low as 12 nm for sparse NW arrays. We clearly verify the 1D sub-band structure in ultrathin NWs by pronounced conductance steps in low-temperature transport measurements using back-gated NW-field effect transistors. Correlated simulations reveal single- and double degenerate conductance steps, which highlight the rotational hexagonal symmetry and reproduce the experimental traces in the diffusive 1D transport limit. Modelling under the realistic back-gate configuration further evidences regimes that lead to asymmetric carrier distribution and breakdown of the degeneracy depending on the gate bias.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Ultrathin InAs nanowires (NW) with a one-dimensional (1D) sub-band structure are promising materials for advanced quantum-electronic devices, where dimensions in the sub-30 nm diameter limit together with post-CMOS integration scenarios on Si are much desired. Here, we demonstrate two site-selective synthesis methods that achieve epitaxial, high aspect ratio InAs NWs on Si with ultrathin diameters below 20 nm. The first approach exploits direct vapor–solid growth to tune the NW diameter by interwire spacing, mask opening size and growth time. The second scheme explores a unique reverse-reaction growth by which the sidewalls of InAs NWs are thermally decomposed under controlled arsenic flux and annealing time. Interesting kinetically limited dependencies between interwire spacing and thinning dynamics are found, yielding diameters as low as 12 nm for sparse NW arrays. We clearly verify the 1D sub-band structure in ultrathin NWs by pronounced conductance steps in low-temperature transport measurements using back-gated NW-field effect transistors. Correlated simulations reveal single- and double degenerate conductance steps, which highlight the rotational hexagonal symmetry and reproduce the experimental traces in the diffusive 1D transport limit. Modelling under the realistic back-gate configuration further evidences regimes that lead to asymmetric carrier distribution and breakdown of the degeneracy depending on the gate bias.
4.
F Del Giudice, J Becker, C De Rose, M Döblinger, D Ruhstorfer, L Suomenniemi, J Treu, H Riedl, J J Finley, G Koblmüller
Ultrathin catalyst-free InAs nanowires on silicon with distinct 1D sub-band transport properties Journal Article
In: Nanoscale, vol. 12, no. 42, pp. 21857-21868, 2020, ISSN: 2040-3364.
@article{nokey,
title = {Ultrathin catalyst-free InAs nanowires on silicon with distinct 1D sub-band transport properties},
author = {F Del Giudice and J Becker and C De Rose and M D\"{o}blinger and D Ruhstorfer and L Suomenniemi and J Treu and H Riedl and J J Finley and G Koblm\"{u}ller},
url = {http://dx.doi.org/10.1039/D0NR05666A},
doi = {10.1039/D0NR05666A},
issn = {2040-3364},
year = {2020},
date = {2020-10-01},
journal = {Nanoscale},
volume = {12},
number = {42},
pages = {21857-21868},
abstract = {Ultrathin InAs nanowires (NW) with a one-dimensional (1D) sub-band structure are promising materials for advanced quantum-electronic devices, where dimensions in the sub-30 nm diameter limit together with post-CMOS integration scenarios on Si are much desired. Here, we demonstrate two site-selective synthesis methods that achieve epitaxial, high aspect ratio InAs NWs on Si with ultrathin diameters below 20 nm. The first approach exploits direct vapor\textendashsolid growth to tune the NW diameter by interwire spacing, mask opening size and growth time. The second scheme explores a unique reverse-reaction growth by which the sidewalls of InAs NWs are thermally decomposed under controlled arsenic flux and annealing time. Interesting kinetically limited dependencies between interwire spacing and thinning dynamics are found, yielding diameters as low as 12 nm for sparse NW arrays. We clearly verify the 1D sub-band structure in ultrathin NWs by pronounced conductance steps in low-temperature transport measurements using back-gated NW-field effect transistors. Correlated simulations reveal single- and double degenerate conductance steps, which highlight the rotational hexagonal symmetry and reproduce the experimental traces in the diffusive 1D transport limit. Modelling under the realistic back-gate configuration further evidences regimes that lead to asymmetric carrier distribution and breakdown of the degeneracy depending on the gate bias.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Ultrathin InAs nanowires (NW) with a one-dimensional (1D) sub-band structure are promising materials for advanced quantum-electronic devices, where dimensions in the sub-30 nm diameter limit together with post-CMOS integration scenarios on Si are much desired. Here, we demonstrate two site-selective synthesis methods that achieve epitaxial, high aspect ratio InAs NWs on Si with ultrathin diameters below 20 nm. The first approach exploits direct vapor–solid growth to tune the NW diameter by interwire spacing, mask opening size and growth time. The second scheme explores a unique reverse-reaction growth by which the sidewalls of InAs NWs are thermally decomposed under controlled arsenic flux and annealing time. Interesting kinetically limited dependencies between interwire spacing and thinning dynamics are found, yielding diameters as low as 12 nm for sparse NW arrays. We clearly verify the 1D sub-band structure in ultrathin NWs by pronounced conductance steps in low-temperature transport measurements using back-gated NW-field effect transistors. Correlated simulations reveal single- and double degenerate conductance steps, which highlight the rotational hexagonal symmetry and reproduce the experimental traces in the diffusive 1D transport limit. Modelling under the realistic back-gate configuration further evidences regimes that lead to asymmetric carrier distribution and breakdown of the degeneracy depending on the gate bias.
3.
D Ruhstorfer, S Mejia, M Ramsteiner, M Döblinger, H Riedl, J J Finley, G Koblmüller
Demonstration of n-type behavior in catalyst-free Si-doped GaAs nanowires grown by molecular beam epitaxy Journal Article
In: Applied Physics Letters, vol. 116, no. 5, pp. 052101, 2020.
@article{,
title = {Demonstration of n-type behavior in catalyst-free Si-doped GaAs nanowires grown by molecular beam epitaxy},
author = {D Ruhstorfer and S Mejia and M Ramsteiner and M D\"{o}blinger and H Riedl and J J Finley and G Koblm\"{u}ller},
url = {https://aip.scitation.org/doi/abs/10.1063/1.5134687},
doi = {10.1063/1.5134687},
year = {2020},
date = {2020-02-04},
journal = {Applied Physics Letters},
volume = {116},
number = {5},
pages = {052101},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
2.
S Fust, A Faustmann, D J Carrad, J Bissinger, B Loitsch, M Döblinger, J Becker, G Abstreiter, J J Finley, G Koblmüller
Quantum-Confinement-Enhanced Thermoelectric Properties in Modulation-Doped GaAs–AlGaAs Core–Shell Nanowires Journal Article
In: Advanced Materials, vol. 32, no. 4, pp. 1905458, 2019, ISSN: 0935-9648.
@article{,
title = {Quantum-Confinement-Enhanced Thermoelectric Properties in Modulation-Doped GaAs\textendashAlGaAs Core\textendashShell Nanowires},
author = {S Fust and A Faustmann and D J Carrad and J Bissinger and B Loitsch and M D\"{o}blinger and J Becker and G Abstreiter and J J Finley and G Koblm\"{u}ller},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.201905458},
doi = {10.1002/adma.201905458},
issn = {0935-9648},
year = {2019},
date = {2019-12-09},
journal = {Advanced Materials},
volume = {32},
number = {4},
pages = {1905458},
abstract = {Abstract Nanowires (NWs) hold great potential in advanced thermoelectrics due to their reduced dimensions and low-dimensional electronic character. However, unfavorable links between electrical and thermal conductivity in state-of-the-art unpassivated NWs have, so far, prevented the full exploitation of their distinct advantages. A promising model system for a surface-passivated one-dimensional (1D)-quantum confined NW thermoelectric is developed that enables simultaneously the observation of enhanced thermopower via quantum oscillations in the thermoelectric transport and a strong reduction in thermal conductivity induced by the core\textendashshell heterostructure. High-mobility modulation-doped GaAs/AlGaAs core\textendashshell NWs with thin (sub-40 nm) GaAs NW core channel are employed, where the electrical and thermoelectric transport is characterized on the same exact 1D-channel. 1D-sub-band transport at low temperature is verified by a discrete stepwise increase in the conductance, which coincided with strong oscillations in the corresponding Seebeck voltage that decay with increasing sub-band number. Peak Seebeck coefficients as high as ≈65\textendash85 µV K−1 are observed for the lowest sub-bands, resulting in equivalent thermopower of S2σ ≈ 60 µW m−1 K−2 and S2G ≈ 0.06 pW K−2 within a single sub-band. Remarkably, these core\textendashshell NW heterostructures also exhibit thermal conductivities as low as ≈3 W m−1 K−1, about one order of magnitude lower than state-of-the-art unpassivated GaAs NWs.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract Nanowires (NWs) hold great potential in advanced thermoelectrics due to their reduced dimensions and low-dimensional electronic character. However, unfavorable links between electrical and thermal conductivity in state-of-the-art unpassivated NWs have, so far, prevented the full exploitation of their distinct advantages. A promising model system for a surface-passivated one-dimensional (1D)-quantum confined NW thermoelectric is developed that enables simultaneously the observation of enhanced thermopower via quantum oscillations in the thermoelectric transport and a strong reduction in thermal conductivity induced by the core–shell heterostructure. High-mobility modulation-doped GaAs/AlGaAs core–shell NWs with thin (sub-40 nm) GaAs NW core channel are employed, where the electrical and thermoelectric transport is characterized on the same exact 1D-channel. 1D-sub-band transport at low temperature is verified by a discrete stepwise increase in the conductance, which coincided with strong oscillations in the corresponding Seebeck voltage that decay with increasing sub-band number. Peak Seebeck coefficients as high as ≈65–85 µV K−1 are observed for the lowest sub-bands, resulting in equivalent thermopower of S2σ ≈ 60 µW m−1 K−2 and S2G ≈ 0.06 pW K−2 within a single sub-band. Remarkably, these core–shell NW heterostructures also exhibit thermal conductivities as low as ≈3 W m−1 K−1, about one order of magnitude lower than state-of-the-art unpassivated GaAs NWs.
1.
J Treu, X Xu, K Ott, K Saller, G Abstreiter, J J Finley, G Koblmüller
Optical absorption of composition-tunable InGaAs nanowire arrays Journal Article
In: Nanotechnology, vol. 30, no. 49, pp. 495703, 2019, ISSN: 0957-4484 1361-6528.
@article{,
title = {Optical absorption of composition-tunable InGaAs nanowire arrays},
author = {J Treu and X Xu and K Ott and K Saller and G Abstreiter and J J Finley and G Koblm\"{u}ller},
url = {http://dx.doi.org/10.1088/1361-6528/ab3ef7},
doi = {10.1088/1361-6528/ab3ef7},
issn = {0957-4484
1361-6528},
year = {2019},
date = {2019-09-20},
journal = {Nanotechnology},
volume = {30},
number = {49},
pages = {495703},
abstract = {InGaAs nanowire (NW) arrays have emerged as important active materials in future photovoltaic and photodetector applications, due to their excellent electronic properties and tunable band gap. Here, we report a systematic investigation of the optical absorption characteristics of composition-tunable vertical InGaAs NW arrays. Using finite-difference time-domain simulations we first study the effect of variable composition (Ga-molar fraction) and NW array geometry (NW diameter, period, fill factor) on the optical generation rate. NWs with typical diameters in the range of ∼100\textendash250 nm lead to generation rates higher than the equivalent bulk case for moderate fill factors (NW period of ∼0.3\textendash0.8 μm), while slightly smaller fill factors and increased diameters are required to maintain high generation rates at increased Ga-molar fraction. The optical absorption was further measured using spectrally resolved ultraviolet\textendashvisible-near-infrared (UV\textendashvis-NIR) spectroscopy on NW arrays transferred to transparent substrates. Interestingly, large variations in Ga-molar fraction (0 \< x(Ga) \< 0.5) have a negligible influence, while minute changes in NW diameter of less than ±20 nm affect the absorption spectra very strongly, leading to pronounced shifts in the peak absorption energies by more than ∼700 meV. These results clearly highlight the much larger sensitivity of the optical absorption behavior to geometric parameters rather than to variations in the electronic band gap of the underlying NW array.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
InGaAs nanowire (NW) arrays have emerged as important active materials in future photovoltaic and photodetector applications, due to their excellent electronic properties and tunable band gap. Here, we report a systematic investigation of the optical absorption characteristics of composition-tunable vertical InGaAs NW arrays. Using finite-difference time-domain simulations we first study the effect of variable composition (Ga-molar fraction) and NW array geometry (NW diameter, period, fill factor) on the optical generation rate. NWs with typical diameters in the range of ∼100–250 nm lead to generation rates higher than the equivalent bulk case for moderate fill factors (NW period of ∼0.3–0.8 μm), while slightly smaller fill factors and increased diameters are required to maintain high generation rates at increased Ga-molar fraction. The optical absorption was further measured using spectrally resolved ultraviolet–visible-near-infrared (UV–vis-NIR) spectroscopy on NW arrays transferred to transparent substrates. Interestingly, large variations in Ga-molar fraction (0 < x(Ga) < 0.5) have a negligible influence, while minute changes in NW diameter of less than ±20 nm affect the absorption spectra very strongly, leading to pronounced shifts in the peak absorption energies by more than ∼700 meV. These results clearly highlight the much larger sensitivity of the optical absorption behavior to geometric parameters rather than to variations in the electronic band gap of the underlying NW array.