Investigation of the epitaxial growth of AIIIBV-N heterostructures for solar cell applications

The InGaAsN/GaAs heterostructures proposed in 1996 by Kondow et al. have been successfully used in telecom laser constructions on GaAs substrate. Additionally, the InGaAsN with a bandgap of 1 eV are lattice matched to both GaAs and Ge for the nitrogen and indium contents of around 3 % and 9 %, respectively. These features make this semiconductor an ideal candidate for high-efficiency multijunction solar cells (MJSCs) based on the Ge/InGaAsN/GaAs/InGaP structure. The growth technology of the GaAsN alloy-based diluted nitrides is very difficult because of the large miscibility gap between GaAs and GaN. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2097

High-pressure Raman scattering in bulk HfS2: comparison of density functional theory methods in layered MS2 compounds (M = Hf, Mo) under compression

We report high-pressure Raman-scattering measurements on the transition-metal dichalcogenide (TMDC) compound HfS2. The aim of this work is twofold: (i) to investigate the high-pressure behavior of the zone-center optical phonon modes of HfS2 and experimentally determine the linear pressure coefficients and mode Grüneisen parameters of this material; (ii) to test the validity of different density functional theory (DFT) approaches in order to predict the lattice-dynamical properties of HfS2 under pressure. For this purpose, the experimental results are compared with the results of DFT calculations performed with different functionals, with and without Van der Waals (vdW) interaction. We find that DFT calculations within the generalized gradient approximation (GGA) properly describe the high-pressure lattice dynamics of HfS2 when vdW interactions are taken into account. In contrast, we show that DFT within the local density approximation (LDA), which is widely used to predict structural and vibrational properties at ambient conditions in 2D compounds, fails to reproduce the behavior of HfS2 under compression. Similar conclusions are reached in the case of MoS2. This suggests that large errors may be introduced if the compressibility and Grüneisen parameters of bulk TMDCs are calculated with bare DFT-LDA. Therefore, the validity of different approaches to calculate the structural and vibrational properties of bulk and few-layered vdW materials under compression should be carefully assessed

Optical markers of magnetic phase transition in CrSBr

Here, we investigate the role of the interlayer magnetic ordering of CrSBr in the framework of $\textit{ab initio}$ calculations and by using optical spectroscopy techniques. These combined studies allow us to unambiguously determine the nature of the optical transitions. In particular, photoreflectance measurements, sensitive to the direct transitions, have been carried out for the first time. We have demonstrated that optically induced band-to-band transitions visible in optical measurement are remarkably well assigned to the band structure by the momentum matrix elements and energy differences for the magnetic ground state (A-AFM). In addition, our study reveals significant differences in electronic properties for two different interlayer magnetic phases. When the magnetic ordering of A-AFM to FM is changed, the crucial modification of the band structure reflected in the direct-to-indirect band gap transition and the significant splitting of the conduction bands along the $\Gamma-Z$ direction are obtained. In addition, Raman measurements demonstrate a splitting between the in-plane modes $B^2_{2g}$/$B^2_{3g}$, which is temperature dependent and can be assigned to different interlayer magnetic states, corroborated by the DFT+U study. Moreover, the $B^2_{2g}$ mode has not been experimentally observed before. Finally, our results point out the origin of interlayer magnetism, which can be attributed to electronic rather than structural properties. Our results reveal a new approach for tuning the optical and electronic properties of van der Waals magnets by controlling the interlayer magnetic ordering in adjacent layers.Comment: 33 pages, 15 figure

High-pressure Raman scattering in bulk HfS2: comparison of density functional theory methods in layered MS2 compounds (M = Hf, Mo) under compression

We report high-pressure Raman-scattering measurements on the transition-metal dichalcogenide (TMDC) compound HfS2. The aim of this work is twofold: (i) to investigate the high-pressure behavior of the zone-center optical phonon modes of HfS2 and experimentally determine the linear pressure coefficients and mode Grüneisen parameters of this material; (ii) to test the validity of different density functional theory (DFT) approaches in order to predict the lattice-dynamical properties of HfS2 under pressure. For this purpose, the experimental results are compared with the results of DFT calculations performed with different functionals, with and without Van der Waals (vdW) interaction. We find that DFT calculations within the generalized gradient approximation (GGA) properly describe the high-pressure lattice dynamics of HfS2 when vdW interactions are taken into account. In contrast, we show that DFT within the local density approximation (LDA), which is widely used to predict structural and vibrational properties at ambient conditions in 2D compounds, fails to reproduce the behavior of HfS2 under compression. Similar conclusions are reached in the case of MoS2. This suggests that large errors may be introduced if the compressibility and Grüneisen parameters of bulk TMDCs are calculated with bare DFT-LDA. Therefore, the validity of different approaches to calculate the structural and vibrational properties of bulk and few-layered vdW materials under compression should be carefully assessed. © 2018, The Author(s).Work supported by the Spanish Government through projects MAT2015-71035-R and FIS2017-83295-P, and by the National Science Centre (NCN) Poland POLONEZ 3 no. 2016/23/P/ST3/04278 and grant OPUS 11 no.2016/21/B/ST3/00482. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 665778. T.W. acknowledges support within the Maestro grant from NCN (no. 2014/14/A/ST3/0065). F. D. acknowledges the support within the FUGA grant from the NCN (No. 2014/12/S/ST3/00313). DFT calculations were performed at ICM at the University of Warsaw, and at ICTJA-CSIC.Peer reviewe

Structural and optical properties of GaSbBi/GaSb quantum wells [Invited]

GaSbBi/GaSb quantum wells (QWs) with Bi content up to 10.1% were grown using molecular beam epitaxy. High crystalline quality and clear interfaces were confirmed by high resolution transmission electron microscopy. The Bi distribution was investigated using energy dispersive X-ray spectroscopy. Room temperature photoluminescence (PL) reveals that the peak energy redshifts at a rate of 32 meV/Bi%, consistent with the theoretical predication using the 8-band kp model. From the temperature dependent PL, it was found that the temperature-insensitivity of the transition from the GaSbBi QW improved with increasing Bi content

Influence of Grain Size on Phase Transitions in Halide Perovskite Films

Grain size in polycrystalline halide perovskite films is known to have an impact on the optoelectronic properties of the films, but its influence on their soft structural properties and phase transitions is unclear. Here, we use temperature-dependent X-ray diffraction, absorption, and macro- and micro-photoluminescence measurements to investigate the tetragonal to orthorhombic phase transition in thin methylammonium lead iodide films with grain sizes ranging from the micron scale down to the tens of nanometre scale. We show that the phase transition nominally at ~150 K is increasingly suppressed with decreasing grain size and, in the smallest grains, we only see the first evidence of a phase transition at temperatures as low as ~80 K. With decreasing grain size, we also see an increasing magnitude of the hysteresis in the structural and optoelectronic properties when cooling to, and then upon heating from, 100K. Our work reveals the remarkable sensitivity of the optoelectronic, physical and phase properties to the local environment of the perovskite structure, which will have large ramifications for phase and defect engineering in operating devices.EPSRC NanoDTC Royal Society ERC Starting Gran

Contactless electroreflectance and theoretical studies of band gap and spin-orbit splitting in InP1-xBix dilute bismide with x <= 0.034

Contactless electroreflectance is applied to study the band gap (E-0) and spin-orbit splitting (Delta(SO)) in InP1-xBix alloys with 0 < x <= 0.034. The E-0 transition shifts to longer wavelengths very significantly (-83 meV/% Bi), while the E0 + Delta(SO) transition shifts very weakly (-13 meV/% Bi) with the rise of Bi concentration. These changes in energies of optical transitions are discussed in the context of the valence band anticrossing model and ab initio calculations. Shifts of E-0 and E-0 + Delta(SO) transitions, obtained within ab-initio calculations, are -106 and -20 meV per % Bi, respectively, which is in a good agreement with experimental results