InSe is a promising material in many aspects where the role of excitons is decisive. Here we report the sequential appearance in its luminescence of the exciton, the biexciton, and the P-band of the ...exciton-exciton scattering while the excitation power increases. The strict energy and momentum conservation rules of the P-band are used to reexamine the exciton binding energy. The new value ≥20 meV is markedly higher than the currently accepted one (14 meV), being however well consistent with the robustness of the excitons up to room temperature. A peak controlled by the Sommerfeld factor is found near the bandgap (~1.36 eV). Our findings supported by theoretical calculations taking into account the anisotropic material parameters question the pure three-dimensional character of the exciton in InSe, assumed up to now. The refined character and parameters of the exciton are of paramount importance for the successful application of InSe in nanophotonics.
In order to analyze why the CIGS (CuInGaSe2) - based solar cells efficiency decrease for wide band gap (high Ga content), we have performed a series of samples by PVD using the three stage process. ...The average compositions of our solar cells range from x = 0 to x = 0.88, as measured by X-ray diffraction. An important feature of this process is to create a double Ga gradient into the absorber, which contributes to improve efficiencies, and this has a major impact on the determination of the sample composition from x-ray diffraction data. We have developed a model in order to assess this impact and question the validity of the compositions extracted from x-ray data. This model allows to get some information about gradient shapes. Using our model, we have obtained some insights on the evolution of the gallium gradient in samples with increasing Ga content, and we determine that this gradient is less pronounced when increasing the amount of gallium. It is a well known fact that this gradient assists the extraction of photocreated carriers, and the modifications of the gallium profile that we have determined may explain, for some part, the degradation of solar cells efficiency for high gallium compositions.
•Explain how average composition determination by x-ray might be flawed.•Demonstrate that group III elements interdiffusion decreases at high Ga content.•Propose a model for analyzing the CIGS (112) x-ray peak versus composition profile.•Evidence the need to grow wide bandgap CIGS at higher temperature than usual.
We have performed a detailed investigation of the photoluminescence features taken at 2
K on a series of Ga
x
In
1−
x
N alloys grown by metal-organic vapour-phase epitaxy through the whole ...composition range. The evolution of the photoluminescence lineshape of GaInN alloys in the indium-rich region is dominated by doping effects rather than by band-gap tailing effects correlated to existence of random chemical crystal inhomogeneities. The lineshape of the photoluminescence indicates a residual electron concentration of about 10
18–10
19
cm
−3 in the bulk part of the epilayers. The value we get for the bowing parameter is
b=2.8
eV.
Phonon dispersion ω(q) and phonon density of states g(ω) of the high‐pressure rocksalt phase of InN are calculated ab initio, at different pressures, using the density functional perturbation theory. ...Born effective charge eT*, LDA values of dielectric constant ε∞ and of the electronic gap Eg are obtained as well. Building on the theoretical knowledge of phonon frequencies and their evolution with pressure, we attempt to interpret the set of six bands found previously in Raman spectra of epitaxial layers and of InN‐nanowires.
In this study, we have used RF-magnetron sputtering to deposit Al-doped ZnO (AZO) nanostructures thin films on poly-ethylene naphthalate (PEN) substrates. The compacted AZO nanopowders with different ...Al concentrations (0, 1, 2, 3 and 4 at.%), which were synthesized by sol–gel method combined with a supercritical drying process, have been used as targets. Structural, optical and electrical properties of deposited thin films with different Al concentrations have been investigated. X-ray diffraction results indicated that all the deposited thin films have hexagonal wurzite structure with c-axis orientation without any secondary phases. The SEM cross section image of the films revealed very dense columnar nanostructure. The best electrical properties (ρ = 4 × 10
−4
Ω cm, µ = 22 cm
2
V
−1
s
−1
, and n
e
= 8 × 10
20
cm
−3
) were obtained for the AZO samples containing 2 at.% of Al. The thin films show an average transmittance of 80 % with the PEN substrate in the visible region.
We report on the growth of GaSe films by molecular beam epitaxy on both (111)B GaAs and sapphire substrates. X-ray diffraction reveals the perfect crystallinity of GaSe with the c-axis normal to the ...substrate surface. The samples grown under Ga rich conditions possess an additional gallium film on top of the monochalcogenide layer. This metallic film shows two normal-to-superconducting transitions which are detected at Tc 1.1 K and 6.0 K. They correspond likely to the β and -phases of gallium in the form of bulk and droplets respectively. Our results demonstrate that van der Waals epitaxy can lead to future high quality hybrid superconductor/monochalcogenide heterostructures.
We have studied plasmon-longitudinal optical (LO) phonon coupled modes by means of Raman scattering in n-type InN layers grown by metalorganic vapor phase epitaxy, for carrier densities in the range ...of 10(19) cm(-3). A strong mode is observed near the frequency of the A(1)(LO) phonon, despite the high conductivity of the films. It is suggested that the main origin which can be invoked for an effective decoupling of the LO phonon from the plasmon is the participation to the scattering of phonons with wave vectors larger than the Thomas-Fermi wave vector. The line shape of the LO mode is calculated using the Lindhard-Mermin dielectric function taking into account finite wave-vectors, for various light scattering processes. We find that the charge density fluctuations mechanism is involved as the main scattering mechanism in n-type InN, at least for the investigated excitation energies in the 2.54-1.89 eV range. The breakdown of the wave-vector conservation is assigned to electron elastic scattering by impurities.
AlxGa1-xN epilayers with x ranging from 0.20 to 0.50 have been grown on c-plane sapphire substrate by metal-organic chemical vapor deposition. The thickness, composition, strain and stress values of ...the AlGaN were determined by high resolution X-ray diffraction. The optical properties of the epilayers were studied using photoluminescence (PL) and reflectivity measurements. The effect of the stress on the bandgap can be explained by room temperature PL. The temperature dependent PL result shows the well-known "S-shape" behavior.
Indium nitride under high pressure up to 50 GPa was analyzed by means of Raman spectroscopy. The wurtzite to rocksalt phase transition was evidenced at the pressure of 13.5±0.5 GPa and the pressure ...dependence of vibration modes of both structures was investigated, leading to the determination of linear pressure coefficients and mode Grüneisen parameters. Influence of the pressure dependence of the energy gap on the spectra intensity is also discussed.
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