Article
Nanoscience & Nanotechnology
David van Treeck, Jonas Laehnemann, Oliver Brandt, Lutz Geelhaar
Summary: In this study, (In,Ga)N shells emitting in the green spectral range were grown around very thin GaN core nanowires using molecular beam epitaxy. A qualitative shell growth model was proposed to explain the influence of growth conditions on the sample morphology and In content. The results showed that with In acting as surfactant, the ternary (In,Ga)N shells exhibited higher thickness uniformity along the nanowire length compared to binary GaN.
Article
Materials Science, Multidisciplinary
Joshua M. McMahon, Emmanouil Kioupakis, Stefan Schulz
Summary: We present an atomistic theoretical study of the competition between Auger and radiative recombination in c-plane (In,Ga)N/GaN quantum wells. The results show that the total Auger recombination rate exhibits a weak temperature dependence, and the hole-hole-electron Auger rate dominates the total rate for different In contents. Our studies provide further insight into the origin of the thermal droop in (In,Ga)N-based light-emitting diodes, suggesting that the competition between radiative and nonradiative recombination is not the driving force behind this droop effect.
Article
Physics, Applied
Purun-hanul Kim, Sang Ho Jeon, Jin Hyuk Jang, Seungwu Han, Youngho Kang
Summary: Micro-light-emitting diodes (mu LEDs) based on GaN are important for future displays, but surface e -h recombination can decrease device efficiency. This study investigates the impact of Ga (VGa) and N (VN) vacancies on the GaN m plane, which are created during the production of one-dimensional GaN structures. The results show that surface VGa doesn't significantly contribute to nonradiative recombination, while surface VN has a deep defect state near the midgap and may act as useful recombination centers due to its low formation energy and small energy barriers for electron and hole capture.
PHYSICAL REVIEW APPLIED
(2023)
Article
Physics, Applied
T. Auzelle, C. Sinito, J. Laehnemann, G. Gao, T. Flissikowski, A. Trampert, S. Fernandez-Garrido, O. Brandt
Summary: We compared the properties of GaN/(Al,Ga)N multiple quantum wells grown by PA MBE and found that different polarity samples are comparable in terms of their morphological and structural perfection. At room temperature, N-polar samples exhibit better performance.
PHYSICAL REVIEW APPLIED
(2022)
Article
Chemistry, Physical
Xuewen Fu, Haixia Nie, Zepeng Sun, Min Feng, Xiang Chen, Can Liu, Fang Liu, Dapeng Yu, Zhimin Liao
Summary: This study investigates the effects of bending strain on the optical and optoelectric properties of gallium nitride nanowires. The results show that bending strain leads to a redshift in the near-band emission spectrum and a linear increase in the photoresponse of the nanowires. The findings provide new insights into the modulation of semiconductor properties and have potential applications in the design of high-performance nano-optoelectric devices.
Article
Optics
A. Pandey, Y. Malhotra, P. Wang, K. Sun, X. Liu, Z. Mi
Summary: This paper demonstrates the performance of N-polar InGaN/GaN nanowire sub-microscale red light emitting diodes (LEDs) for the first time. These LEDs exhibit higher efficiency and brightness compared to conventional red-emitting micro-LEDs. In-situ annealing significantly enhances the optical emission intensity, and the fabricated LED sizes are extremely small.
PHOTONICS RESEARCH
(2022)
Article
Chemistry, Multidisciplinary
Alica Rosova, Edmund Dobrocka, Peter Elias, Stanislav Hasenohrl, Michal Kucera, Filip Gucmann, Jan Kuzmik
Summary: In this study, (Ga)N epitaxial layers were successfully grown on sapphire substrates using organometallic chemical vapor deposition. The large pyramids, which were randomly distributed, were found to be grown above edge-type dislocations originating from the GaN buffer. These large pyramids exhibited good crystallinity and a small number of defects, making them potentially useful in various applications.
Article
Nanoscience & Nanotechnology
Remy Vermeersch, Gwenole Jacopin, Florian Castioni, Jean-Luc Rouviere, Alberto Garcia-Cristobal, Ana Cros, Julien Pernot, Bruno Daudin
Summary: The growth and optical properties of GaN quantum disks in AlN nanowires were studied via molecular beam epitaxy to control the emission wavelength of AlN nanowire-based LEDs. In addition to GaN quantum disks with thickness ranging from 1 to 4 monolayers, focus was given to incomplete GaN disks with lateral confinement. Their emission spectrum consists of sharp lines extending down to 215 nm near the AlN band edge. The room temperature cathodoluminescence intensity of GaN quantum disks embedded in AlN nanowires is about 20% of the low temperature value, highlighting the potential of ultrathin/incomplete GaN quantum disks for deep UV emission.
Article
Crystallography
Youhua Zhu, Tao Hu, Meiyu Wang, Yi Li, Mei Ge, Xinglong Guo, Honghai Deng, Zhitao Chen
Summary: InAlN/GaN heterostructures were successfully grown on GaN/sapphire and AlN/sapphire substrates using metal organic chemical vapor deposition. The epitaxial quality was confirmed by X-ray diffraction, and transmission electron microscopy characterized micro-structural propagation defects originating from extended threading dislocations in the GaN layer. Cathodoluminescence peak shifting was observed with increasing acceleration voltage, attributed to factors such as inhomogeneous composition and internal absorption. Optimization of the structural parameters of the epilayers is expected to improve epitaxial quality and optoelectronic device design.
Article
Chemistry, Multidisciplinary
Pierre Lottigier, Davide Maria Di Paola, Duncan T. L. Alexander, Thomas F. K. Weatherley, Pablo Saenz de Santa Maria Modrono, Danxuan Chen, Gwenole Jacopin, Jean-Francois Carlin, Raphael Butte, Nicolas Grandjean
Summary: By inserting an In-containing underlayer during the growth of InGaN quantum wells (QWs) on thin GaN buffer layers, the emission efficiency of the QWs on silicon substrates is significantly increased. This study also reveals the crucial role of point defects in limiting the efficiency of InGaN QWs, even with a lower density compared to threading dislocations.
Article
Physics, Applied
Jianping Wang, Fangyuan Shi, Xingzhi Wu, Junyi Yang, Yongqiang Chen, Quanying Wu, Yinglin Song, Yu Fang
Summary: The effect of Fe defects on carrier recombination and two-photon induced ultrafast exciton dynamics in GaN crystals was investigated using femtosecond transient absorption spectroscopy. The absorption kinetics exhibited different characteristics under different nonequilibrium carrier concentrations and distributions. The findings are crucial for the applications of GaN in ultrafast optoelectronics and integrated nonlinear optics.
APPLIED PHYSICS LETTERS
(2023)
Article
Optics
Poulami Ghosh, Dapeng Yu, Gaomin Li, Mingyuan Huang, Yingkai Liu
Summary: Through various optical measurements, it was found that the decrease in diameter of gallium nitride microrods results in a blueshift in the band gap energy due to the formation of whispering gallery mode polaritons. Raman spectra confirmed that the band gap energy changes were not due to stress/strain or different doping concentrations. Photoluminescence experiments revealed that the exciton photon coupling strength depends on the microrod diameter and decreases as the diameter decreases.
Article
Chemistry, Multidisciplinary
Eitan Oksenberg, Calvin Fai, Ivan G. Scheblykin, Ernesto Joselevich, Eva L. Unger, Thomas Unold, Charles Hages, Aboma Merdasa
Summary: Understanding energy transport in metal halide perovskites is crucial for optimizing materials and device designs. Difficulties in distinguishing between charge carrier diffusion, photon recycling, and photon transport have led to conflicting reports. This study uses CsPbBr3 nanowires to demonstrate that charge carrier diffusion dominates energy transport in perovskites over photon recycling.
ADVANCED FUNCTIONAL MATERIALS
(2021)
Article
Physics, Multidisciplinary
Rui Li, Ming-Sheng Xu, Peng Wang, Cheng-Xin Wang, Shang-Da Qu, Kai-Ju Shi, Ye-Hui Wei, Xian-Gang Xu, Zi-Wu Ji
Summary: The photoluminescence spectra of two different green InGaN/GaN multiple quantum well samples with varying growth temperatures were analyzed under different excitation powers and temperatures, showing different emission characteristics related to the In content and lattice mismatch induced by growth temperature.
Article
Materials Science, Multidisciplinary
V. Janardhanam, Jong-Hee Kim, I. Jyothi, Min-Sung Kang, Sang-Kwon Lee, Chel-Jong Choi
Summary: We fabricated a PtSe2/n-type GaN heterojunction diode by transferring a large-scale grown two-dimensional PtSe2 film onto a GaN substrate. Temperature-dependent measurements revealed a strong dependence of the ideality factor and barrier height on the measurement temperature, indicating the presence of barrier inhomogeneities along the interface. The temperature-dependency of the reverse leakage current showed different conduction mechanisms in different temperature regions, and the interface state density determined from capacitance measurements was found to be lower than that obtained from forward I-V characteristics.
Article
Chemistry, Physical
Y. Takagaki, M. Hanke, M. Ramsteiner, J. Laehnemann
Summary: Films of transition-metal-chalcogen alloys were produced using hot wall epitaxy, and the influences of the coexistence of Sb in the alloys on the electrical properties of the films were investigated.
JOURNAL OF ALLOYS AND COMPOUNDS
(2023)
Article
Physics, Applied
Kingsley Egbo, Esperanza Luna, Jonas Laehnemann, Georg Hoffmann, Achim Trampert, Jona Gruembel, Elias Kluth, Martin Feneberg, Ruediger Goldhahn, Oliver Bierwagen
Summary: By combining SnO2 and Sn, we successfully grew phase-pure single-crystalline metastable SnO (001) thin films on Y-stabilized ZrO2 (001) substrates using suboxide molecular beam epitaxy (S-MBE) at a growth rate of about 1.0 nm/min without additional oxygen. These films exhibit epitaxial growth over a wide temperature range of 150 to 450°C. The obtained p-type SnO films at low substrate temperatures show promise for back-end-of-line (BEOL) compatible applications and integration with n-type oxides in pn heterojunctions and field-effect transistors.
JOURNAL OF APPLIED PHYSICS
(2023)
Article
Nanoscience & Nanotechnology
M. Oliva, V Kaganer, M. Pudelski, S. Meister, A. Tahraoui, L. Geelhaar, O. Brandt, T. Auzelle
Summary: We present a simple method for fabricating ordered arrays of GaN nanowires with high aspect ratios and small diameters. The process involves lithographic patterning, dry and wet etching, and utilizes a bilayer Ni/SiNx hard mask. The resulting nanowires are highly uniform and suitable for photonic applications. However, nanowire breaking or bundling occurs for diameters below approximately 20 nm, which is attributed to capillary forces during drying. Overall, the process shows good compatibility with optoelectronic applications and allows for regrowth after mask removal.
Article
Physics, Applied
Duc V. Dinh, Jonas Laehnemann, Lutz Geelhaar, Oliver Brandt
Summary: Using high-resolution x-ray diffractometry, the lattice parameters of undoped ScxAl1-xN layers grown on GaN templates were determined. The Sc content x of the layers was measured independently and ranged from 0 to 0.25. The in-plane lattice parameter of the layers increased linearly with increasing x, while the out-of-plane lattice parameter remained constant. Layers with x≈0.09 were lattice matched to GaN, resulting in a smooth surface and comparable structural perfection. In addition, a two-dimensional electron gas was induced at the ScxAl1-xN/GaN heterointerface, with the highest sheet electron density and mobility observed for lattice-matched conditions.
APPLIED PHYSICS LETTERS
(2023)
Article
Physics, Applied
Kingsley Egbo, Jonas Laehnemann, Andreas Falkenstein, Joel Varley, Oliver Bierwagen
Summary: (La and Ga)-doped tin monoxide thin films were grown with dopant concentrations ranging from approximate to 5 x 10(18) to 2 x 10(21) cm(-3). Ga acted as an acceptor and La as a compensating donor in the doped samples. The results show the possibilities of controlling the hole concentration in p-type SnO, which can be useful for a range of optoelectronic and gas-sensing applications.
APPLIED PHYSICS LETTERS
(2023)
Article
Nanoscience & Nanotechnology
T. Auzelle, M. Oliva, P. John, M. Ramsteiner, A. Trampert, L. Geelhaar, O. Brandt
Summary: The self-assembly of GaN nanowires on TiN(111) substrates is examined using SiN x patches as nucleation seeds. The density of the nanowires can be tuned by three orders of magnitude by varying the amount of pre-deposited SiN x , bridging the density regimes achievable by direct self-assembly with MBE or MOVPE. This approach has potential applications in tuning the density of III-V semiconductors grown on inert surfaces like 2D materials.
Article
Chemistry, Multidisciplinary
Vladimir M. Kaganer, Oleg Konovalov, Gabriele Calabrese, David van Treeck, Albert Kwasniewski, Carsten Richter, Sergio Fernandez-Garrido, Oliver Brandt
Summary: GaN nanowires grown on Ti films sputtered on Al2O3 were studied using X-ray diffraction and grazing-incidence small-angle X-ray scattering. Different crystallites, including Ti, TiN, Ti3O, Ti3Al, and Ga2O3, were observed in the Ti film. The GaN nanowires exhibited a high degree of epitaxial orientation with the substrate due to the topotaxial crystallites in the Ti film. The size distributions and relative fractions of different side facets of the nanowires were determined using the Monte Carlo method and GISAXS.
JOURNAL OF APPLIED CRYSTALLOGRAPHY
(2023)
Article
Nanoscience & Nanotechnology
David van Treeck, Jonas Laehnemann, Oliver Brandt, Lutz Geelhaar
Summary: In this study, (In,Ga)N shells emitting in the green spectral range were grown around very thin GaN core nanowires using molecular beam epitaxy. A qualitative shell growth model was proposed to explain the influence of growth conditions on the sample morphology and In content. The results showed that with In acting as surfactant, the ternary (In,Ga)N shells exhibited higher thickness uniformity along the nanowire length compared to binary GaN.
Article
Nanoscience & Nanotechnology
P. John, M. Gomez Ruiz, L. van Deurzen, J. Laehnemann, A. Trampert, L. Geelhaar, O. Brandt, T. Auzelle
Summary: This study investigates the molecular beam epitaxy of AlN nanowires and identifies 1150 degrees C as the optimal growth temperature. The growth process involves the grain growth of the TiN film and the formation of preferred {111} facets for AlN nucleation. Luminescence experiments on the nanowires reveal a steep increase in deep-level signals above 1050 degrees C, potentially due to oxygen incorporation from the Al2O3 substrate.
Article
Nanoscience & Nanotechnology
David van Treeck, Jonas Laehnemann, Guanhui Gao, Sergio Fernandez Garrido, Oliver Brandt, Lutz Geelhaar
Summary: Taking advantage of directed atomic fluxes in molecular beam epitaxy, we have developed a method for sequentially depositing lateral (In, Ga)N shells on GaN nanowires. By manipulating the growth temperature and the In/Ga flux ratio, we have systematically investigated the incorporation of In and the resulting emission spectra.
Article
Nanoscience & Nanotechnology
L. van Deurzen, J. Singhal, J. Encomendero, N. Pieczulewski, C. S. Chang, Y. Cho, D. A. Muller, H. G. Xing, D. Jena, O. Brandt, J. Laehnemann
Summary: Using low-temperature cathodoluminescence spectroscopy, the properties of N- and Al- polar AlN layers grown on bulk AlN{0001} by molecular beam epitaxy are studied. Both polarities of layers exhibit a suppression of deep-level luminescence compared to the bulk AlN substrate, a total absence of the prevalent donor with an exciton binding energy of 28 meV, and a much increased intensity of the emission from free excitons. The dominant donor in these layers has an associated exciton binding energy of 13 meV. Additionally, the observation of excited exciton states up to the exciton continuum allows for the direct extraction of the Γ(5) free exciton binding energy of 57 meV.
Article
Nanoscience & Nanotechnology
Miriam Oliva, Timur Flissikowski, Michal Gora, Jonas Lahnemann, Jesus Herranz, Ryan B. Lewis, Oliver Marquardt, Manfred Ramsteiner, Lutz Geelhaar, Oliver Brandt
Summary: In this study, the spontaneous emission of zincblende GaAs/(Al,Ga)As core/shell nanowires was investigated using mu-photoluminescence spectroscopy. The results revealed the low degree of polytypism and high efficiency of these nanowires in terms of their internal quantum efficiency, extraction efficiency, and dependence on carrier density and temperature. Furthermore, the methodology established in this study can be applied to nanowires of other materials systems for optoelectronic applications.
ACS APPLIED NANO MATERIALS
(2023)
