Thermodynamics of type A1−xBxC1−yDy III–V quaternary solid solutions

An improved theory based on the pair approximation is given for the thermodynamic properties of type A_1?xB_xC_1?yD_yIII–V quaternary solid solutions. The theory takes into account the quasi-chemical nature of the nearest neighbor pair distribution, which has been neglected or inadequately treated in previous work. With a suitable thermodynamic treatment, a quasi-chemical equilibrium relation for the nearest neighbor pair distribution is derived. Numerical calculations using available thermodynamic data show that the distribution will deviate appreciably from random mixing values in the In_1?xGa_xP_1?yAs_y and Al_1?xGa_xAs_1?ySb_y systems due to a short-range clustering effect of nearest neighbor pairs with strong bond energy, whereas the deviation will be small in the Al_1?xGa_xP_1?yAS_y system. The expressions for the chemical potentials and the activity coefficients of the binary compound components are given. These are readily applicable to phase diagram calculations.     

Substrate effect on the electronic structure in GaxIn1−xAsySb1−y/GaSb and GaxIn1−xAsySb1−y/InAs

We present a theoretical study of the substrate effect on electronic structure in cubic Ga_xIn_1−xAs_ySb_1−y lattice-matched to GaSb and InAs. Our calculations are based on the empirical pseudopotential formalism within the virtual crystal approximation where the effect of disorder is taken into account. We show that the electronic band structure of the quaternary alloy Ga_xIn_1−xAs_ySb_1−y is altered by the change of substrate for the entire range of alloy compositions x. Moreover, we find that at Ga concentrations (x≤0.8), the ionicity is less important when Ga_xIn_1−xAs_ySb_1−y is lattice-matched to GaSb instead of InAs. The information will be useful for the choice of substrate in the composition range 0–1 and hence for the determination of the lattice-matching conditions for Ga_xIn_1−xAs_ySb_1−y quaternary materials.     

Evidence by Raman scattering on In1−xGaxAsyP1−y of the two-mode behaviour of In1−xGaxP

We report the Raman scattering study of optical vibrations in indium rich In_1?xGa_xAs_yP_1?y epitaxial layers grown on InP. We evidence the splitting of the LO line of InP even for very small x and demonstrate it is due to the presence of gallium in the samples. These results lead us to ascribe to In_1?xGa_xP a somewhat modified two-mode behaviour and to In_1?xGa_xAs_yP_1?y a four-mode behaviour.     

Structural and electronic properties of zincblende phase of Tl x Ga1−x As y P1−y quaternary alloys: First-principles study

Using the first-principles band-structure method, we have calculated the structural and electronic properties of zincblende TlAs, TlP, GaAs and GaP compounds and their new semiconductor Tl _x Ga_1?x As _y P_1?y quaternary alloys. Structural properties of these semiconductors are obtained with the Perdew and Wang local-density approximation. The lattice constants of Tl _x Ga_1?x As, Tl _x Ga_1?x P ternary and Tl _x Ga_1?x As _y P_1?y quaternary alloys were composed by Vegard’s law. Our investigation on the effect of the doping (Thallium and Arsenic) on lattice constants and band gap shows a non-linear dependence for Tl _x Ga_1?x As _y P_1?y quaternary alloys. The band gap of Tl _x Ga_1?x As _y P_1?y , E _g (x, y) concerned by the compositions x and y. To our awareness, there is no theoretical survey on Tl _x Ga_1?x As _y P_1?y quaternary alloys and needs experimental verification.     

X-ray diffraction studies of heterostructures based on solid solutions Al x Ga1 − x As y P1 − y : Si

The growth of MOCVD-hydride epitaxial heterostructures based on ternary solid solutions Al _x Ga_1?x As heavily doped with phosphorus and silicon has been studied using high-resolution X-ray diffraction and X-ray microanalysis. The prepared epitaxial films are five-component solid solutions (As _x Ga_1?x As _y P_{1 ? y} )_{1 ? z} Si _z .     

Principal energy band gaps of the quaternary alloy AlxGa1−xSbyAs1−y

The correlated function expansion (CFE) interpolation procedure was presented to efficiently estimate principal energy band gaps and lattice constants of the quaternary alloy Al_xGa_1−xSb_yAs_1−y over the entire composition variable space. The lattice matching conditions between x and y for the alloy Al_xGa_1−xSb_yAs_1−y substrated to InAs and GaSb were obtained by optimizing the alloy lattice constant to that of the substrates. The corresponding principal band gaps (E(Γ), E(L), and E(X)) were also calculated along the lattice matching condition on each substrate (InAs and GaSb).     

Vibrational spectra of one-dimensional mass-disordered quaternary alloys

The spectral density of vibrational states for one-dimensional mass-disordered quaternary alloys A_yB_1?yC_1?xD_x is evaluated using the negative eigenvalue theorem. Spectra for masses corresponding to Al_yGa_1?yAs_1?xP_x are presented.     

Investigation of defect-related optical properties in AlxInyGa1−x−yN quaternary alloys with different Al/In ratios

Al_xIn_yGa_1?x?yN quaternary alloys with different ratios of Al/In were grown by metal-organic chemical vapor deposition on GaN/Al₂O₃ substrates. The structural and emission properties of the as-grown samples were investigated, respectively, by high-resolution X-ray diffraction and photoluminescence (PL) measurements. The PL emission character is related to the two prominent quenching bands, which have been determined to be located at around 1.1 eV and 1.7 eV above the valence band, respectively, by the method of optical quenching of photoconductivity. PL emission is most intense when the Al/In ratio is 7.5 for the Al_xIn_yGa_1?x?yN layer. In addition, a stronger quenching phenomenon with Al/In ratio of 5.0 in Al_xIn_yGa_1?x?yN is observed in accordance with a reduction of the intensity of Al_xIn_yGa_1?x?yN-related emission peak.     

Elastic constants and mechanical stability of InxAl1 − xAsySb1 − y lattice-matched to different substrates

Based on a pseudopotential approach under the virtual crystal approximation, the elastic modulus of In_xAl_1???xAs_ySb_1???y quaternaries lattice-matched to InP, GaSb and InAs substrates has been investigated. Our findings show a reasonably good accord with experiment. The dependence of the elastic features of interest on the indium concentration x shows a monotonic behaviour when In_xAl_1???xAs_ySb_1???y is lattice-matched to InP substrate. In that case, the elastic constants have larger values and the material system of interest becomes less harder and its rigidity becomes weaker. The mechanical stability criteria is verified in terms of elastic constants and shows that In_xAl_1???xAs_ySb_1???y is mechanically stable for each x and substrate being considered here. The change in indium content x and the substrate is found to have no much effect on both the Poisson ratio and machinability. The present study showed that a proper choice of the indium composition x and substrate may provide more diverse opportunities as regards the elastic modulus of In_xAl_1???xAs_ySb_1???y.     

Pressure experiment determination of the direct-indirect transition in the quarternary In1−xGaxP1−zAsz

Spontaneous and laser emission from In_1-xGa_xP_1-zAs_z double heterojunction diodes near the direct-indirect crossover (E_Γ = E_X, x ≡ x_c, z ≡ z_c) are studied at 77°K as a function of hydrostatic pressure up to 6 kbar. The pressure coefficients of the spontaneous emission peaks and of the laser modes are ～- 10.5 × 10^-6 eV/bar which is characteristics of the Γ band edge in III–V semiconductors. Laser threshold current is found to rise rapidly as pressure is applied owing to the decreasing Γ-X separation and the resultant carrier transfer to the X minima. Experimental lower limits for the direct-indirect crossover at three points in the In_1-xGa_xP_1-zAs_z quaternary system are determined. These three points and the established crossover in GaAs_1-yP_y (y_c ≈ 0.46, 77°K) give for the quaternary crossover (77°K) x_c ? 0.52z_c = 0.72. and the value x_c ≈ 0.72 for the limiting case of In_1-xGa_xP. Band edge bowing effects along the direct-indirect crossover in the In_1-xGa_xP_1-zAs_z system are discussed. The highest energy laser (77°K) for this quaternary system is estimated from pressure measurements to be ～ 2.155 eV (5752 Å).     

The effect of compositional disorder on electronic band structure in GaxIn1 − xAsySb1 − yalloys lattice matched to GaSb

A pseudopotential formalism coupled with the virtual crystal approximation are applied to study the effect of compositional disorder upon electronic band structure of cubic Ga_xIn_1 − xAs_ySb_1 − yquarternary alloys lattice matched to GaSb. The effects of compositional variations are properly included in the calculations. Our theoretical results show that the compositional disorder plays an important role in the determination of the energy band structure of Ga_xIn_1 − xAs_ySb_1 − y/GaSb and that the bowing parameter is dominated by the group V-anion-based sublattice. Moreover, the absorption at the fundamental optical gaps is found to be direct within a whole range of the x composition.     

Gas source molecular beam epitaxial growth model for Ga x In1−x As y P1−y on GaAs

A gas source molecular beam epitaxial (GSMBE) growth model considering an intermediate InGaAsP state is presented. This model is very simple and needs only two fitting parameters, k _In and k _Ga, which are determined experimentally from In_1-x Ga _x As _y P_1-y on InP (0<x<0.47 and 0<y<1). At a growth temperature of 480°C, k _In and k _Ga are 28 and 3 respectively. The temperature dependencies of k _In and k _Ga are also studied: the fitted activation energies are-30 and 330 meV, respectively. Using these parameters, the model is used to predict the AsH₃ and PH₃ flow rates for growing In_1-x Ga _x As _y P_1-y on GaAs (0.51<x<1 and 0<y<1). The lattice mismatch of all the epilayers grown is within 6×10^-4. This indicates that this simple GSMBE model covers the whole compositional range of lattice-matched and coherently strained InGaAsP.     

Antisite defects in Inl−yGayAsl−xPx

The dependences on alloy compositions x and y are predicted for the deep energy levels of antisite defects in the quaternary alloys In_l?yGa_yAs_l?xP_x.     

Resonant enhancement (?) of the recombination probability at the nitrogen-trap, Γ-band edge crossover in GaAs1−xPx: N(EN = EΓ, x ≡ xN)

Previously it has been suggested on theoretical grounds and early data on N-doped In_1?xGa_xP that at the point of degeneracy of the Γ band edge and the N-trap (x ≡ x_N) the electron-hole recombination probability associated with the trap is resonantly enhanced by the presence of Γ band states. Data are presented on N-doped and N-free In_1?xGa_xP_1?zAs_z/ GaAs_1?yP_y (x ～ 0.70, y ≈ 0.40, z ～ 0.01) single heterojunction laser diodes fabricated on the same VPE GaAs_1?yP_y:N system, where the position of the N trap is well known, indicate that the N trap weakens the band-to-band (Γ) transition and is not itself enhanced beyond the usual band structure enhancement (BSE) described recently for ternary alloys. A theoretical argument is offered to explain the discrepancy between earlier theory and experimental observations.     

Momentum matrix elements in III–V semiconductor alloys

The composition dependence of P², the square of the principal interband matrix element, is investigated. P² is calculated in a virtual crystal approximation within the empirical pseudopotential method. In all the alloys studied, the variation of P² with x is found to be nearly linear. The results are compared with experimental values, obtained from a five-band $\text{K}$, $\text{K}$ analysis of the conduction electron Landé factor and effective mass data. The agreement is good in Ga_1?xIn_xAs and Ga_1?xAl_xAs, but not in In_1?xGa_xSb, which shows a disorder induced deviation.     

Electron beam epitaxy of alloy semiconductors

Abstract

It was investigated that, when an Al evaporated layer on a GaP (GaAs, GaAs_1?y P _y ) substrate was bombarded with total fluences of 0.1?1.0 × 10¹⁸ electrons cm^?2 at 7 MeV and at 50°C, a thin heteroepitaxial layer of Al _x Ga_1?x P (Al _x Ga_1?x As, Al _x Ga_1?x As_1?y P _y ) crystal was grown on S-doped (111), (100) and (110) GaP [(110) Cr, O-doped GaAs, (100) Te-doped GaAS_1?y P _y ] substrates.

Evidence for the creation of the epilayers before annealing was obtained from measurements using an X-ray diffractometer, an X-ray photoelectron spectrometer, a reflection high-energy electron diffractometer, a transmission electron microscope and a scanning transmission electron microscope. In the case of Al/GaP, the epitaxial layers of Al_～0.25Ga_～0.75P, Al_～0.5Ga_～0.5P and Al_～0.75Ga_～0.25P were grown on (111), (100) and (110) GaP substrates, respectively. Their compositions did not vary with the total electron fluence.     

First principles study on electronic and optical properties of Al<Subscript>x</Subscript>Ga<Subscript>1−x</Subscript>N and In<Subscript>y</Subscript>Ga<Subscript>1−y</Subscript>N

The band structure, density of states of Al_xGa_1?xN and In_yGa_1?yN was performed by the first-principles method within the local density approximation. The calculated energy gaps of the AlN, Al_0.5Ga_0.5N, GaN, In_0.5Ga_0.5N and InN were 5.48, 4.23, 3.137, 1.274 and 0.504 eV, which were in agreement with the experimental result. The dielectric functions, absorption coefficient and loss function were calculated based on Kramers–Kronig relations. Further more, the relationships between electronic structure and optical properties were investigated theoretically. For Al_xGa_1?xN and In_yGa_1?yN materials, the micromechanism of the optical properties were explained.     

Numerical optimization of In-mole fractions and layer thicknesses in AlxGa1−xN/AlN/GaN high electron mobility transistors with InGaN back barriers

The effects of the In-mole fraction (x) of an In_xGa_1−xN back barrier layer and the thicknesses of different layers in pseudomorphic Al_yGa_1−yN/AlN/GaN/In_xGa_1−xN/GaN heterostructures on band structures and carrier densities were investigated with the help of one-dimensional self-consistent solutions of non-linear Schrödinger-Poisson equations. Strain relaxation limits were also calculated for the investigated Al_yGa_1−yN barrier layer and In_xGa_1−xN back barriers. From an experimental point of view, two different optimized structures are suggested, and the possible effects on carrier density and mobility are discussed.     

Interband emission energy in a dilute nitride quaternary semiconductor quantum dot for longer wavelength applications

Excitonic properties are studied in a strained Ga_1−xIn_xN_yAs_1−y/GaAs cylindrical quantum dot. The optimum condition for the desired band alignment for emitting wavelength 1.55 µm is investigated using band anticrossing model and the model solid theory. The band gap and the band discontinuities of a Ga_1−xIn_xN_yAs_1−y/GaAs quantum dot on GaAs are computed with the geometrical confinement effect. The binding energy of the exciton, the oscillator strength and its radiative life time for the optimum condition are found taking into account the spatial confinement effect. The effects of geometrical confinement and the nitrogen incorporation on the interband emission energy are brought out. The result shows that the desired band alignment for emitting wavelength 1.55 µm is achieved for the inclusion of alloy contents, y=0.0554% and x=0.339% in Ga_1−xIn_xN_yAs_1−y/GaAs quantum dot. And the incorporation of nitrogen and indium shows the red-shift and the geometrical confinement shows the blue-shift. And it can be applied for fibre optical communication networks.     

Numerical analysis of the short-circuit current density in GaInAsSb thermophotovoltaic diodes

In this paper, a simulation and analysis on the short-circuit current density (J_sc) of the P-GaSb window/P-Ga_xIn_1−xAs_1−ySb_y emitter/N-Ga_xIn_1−xAs_1−ySb_y base/N-GaSb substrate structure is performed. The simulations are carried out with a fixed spectral control filter at a radiator temperature (T_rad) of 950 °C, diode temperature (T_dio) of 27 °C and diode bandgap (E_g) of 0.5 eV. The radiation photons are injected from the front P-side. Expressions for minority carrier mobility and absorption coefficient of Ga_xIn_1−xAs_1−ySb_y semiconductors are derived from Caughey–Thomas and Adachi’s model, respectively. The P-Ga_xIn_1−xAs_1−ySb_y emitter with a much longer diffusion length is adopted as the main optical absorption region and the N-Ga_xIn_1−xAs_1−ySb_y base region contribute little to J_sc. The effect of P-GaSb window and P-Ga_xIn_1−xAs_1−ySb_y emitter region parameters on J_sc is mainly analyzed. Dependence of J_sc on thickness and carrier concentration of the window are analyzed; these two parameters need to be properly selected to improve J_sc. Contributions from the main carrier recombination mechanisms in the emitter region are considered; J_sc can be improved by suppressing the carrier recombination rate. Dependence of J_sc on the carrier concentration and layer thickness of the emitter P-region are also analyzed; these two parameters have strong effect on J_sc. Moreover, adding a back surface reflector (BSR) to the diode can improve J_sc. The simulated results are compared with the available experimental data and are found to be in good agreement. These theoretical simulations help us to better understand the electro-optical behavior of Ga_xIn_1−xAs_1−ySb_y TPV diode and can be utilized for performance enhancement through optimization of the device structure.