Composition Dependence Of Band Gap Research Articles

Density functional study on structural and optoelectronic properties of cubic $$\hbox {Mg}_{x}\hbox {Zn}_{1-x}\hbox {S}_{y}\hbox {Se}_{1-y}$$ semiconductor quaternary alloys

In the case of technologically important quaternary alloys, structural and optoelectronic properties have been calculated with density functional theory (DFT)-based full-potential linearised augmented plane-wave (FP-LAPW) approach. The Perdew–Burke–Ernzerhof generalised gradient approximation (PBE-GGA) for structural properties and both the modified-Becke–Johnson (mBJ) and Engel and Vosko GGA (EV-GGA) for optoelectronic properties are employed to calculate the respective exchange-correlation potentials. Each specimen within the quaternary system is a direct band-gap – semiconductor. The lattice constant decreases, while bulk modulus and band gap increase nonlinearly with increasing anionic (S) concentration at each cationic (Mg) concentration . On the other hand, nonlinear increment in lattice constant and band gap, but decrement in bulk modulus is found with increase in cationic concentration at each anionic concentration . Calculated contour maps for lattice constants and energy band gaps would be useful in fabricating new quaternary alloys with preferred optoelectronic features. Optical properties of the specimens within the quaternary system show several interesting features. , 4p and 4p optical excitations contribute intense peaks in each spectrum. The composition dependence of each calculated zero-frequency limit shows opposite trend, while each calculated critical point shows similar trend of composition dependence of band gap. Moreover, calculations suggest the possibility of growth of several cubic quaternary specimens on GaAs and InP substrates.

First principle investigations of structural and optoelectronic features of cubic CdxZn1−xSyTe1-y quaternary semiconductor alloys

In case of technologically important CdxZn1−xSyTe1−y quaternary alloys, structural and optoelectronic properties have been calculated for the first time with DFT based FP-LAPW approach. The PBE-GGA functional for structural properties and mainly the mBJ functional for optoelectronic properties are employed to calculate respective exchange-correlation potentials. Each specimen within CdxZn1−xSyTe1−y quaternary system is a direct band gap (Γ-Γ) semiconductor. The lattice constant reduces, while bulk modulus and band gap enhances nonlinearly with increasing anionic (S) concentration y at each cationic (Cd) concentration x. On the other hand, nonlinear increase in lattice constant, but decrease in bulk modulus and band gap is observed with increase in cationic concentration x at each anionic concentration y. Calculated contour maps for lattice constants and energy band gaps would be useful in fabricating new ternary or quaternary alloys with preferred optoelectronic features. Optical properties of the said specimens within CdxZn1−xSyTe1−y quaternary system show several interesting features. The composition dependence of each calculated zero-frequency limit shows opposite trend, while each calculated critical point shows similar trend of composition dependence of band gap. Moreover, calculations suggest the possibilities of growth of several zinc-blende (B3) CdxZn1−xSyTe1−y quaternary specimens on ZnTe, InP and GaAs substrates.

Structural and optoelectronic properties of cubic MgxZn1−xSyTe1-y semiconductor quaternary alloys-a first principles investigation

Density functional calculations of structural and optoelectronic properties of cubic MgxZn1−xSyTe1−y quaternary alloys are performed with mBJ, EV-GGA and PBE-GGA functional. Each quaternary specimen is direct band gap (Γ-Γ) semiconductor. Lattice constant reduces, while bulk modulus and band gap enhances nonlinearly with increase in S-concentration y at each Mg-concentration x. Again, nonlinear increment in lattice constant and band gap, but reduction in bulk modulus is found with increase in Mg-concentration x at each S-concentrations y. Contour plots for lattice constants and band gaps would be useful in fabricating new quaternary alloys with preferred optoelectronic features. Chalcogen-p→Zn-5s,4p; Mg-4s,4p optical excitations contribute intense peaks in each ε2(ω) spectra. Composition dependence of each calculated zero-frequency limit shows opposite trend, while each calculated critical point shows similar trend of composition dependence of band gap. Calculations also suggested the possibility of growth of several said quaternary alloys on ZnTe, InAs and InP substrates.

First principles investigations of structural and optoelectronic properties of cubic MgxZn1−xSeyTe1−y quaternary semiconductor alloys using FP-LAPW approach

Structural and optoelectronic properties of technologically important MgxZn1−xSeyTe1−y quaternary alloys are calculated employing DFT-based FP-LAPW approach. Computations of exchange–correlation potentials are performed with PBE-GGA for structural properties and both the mBJ and EV-GGA for optoelectronic properties. Each specimen within MgxZn1−xSeyTe1−y system is a direct band gap (Γ–Γ) semiconductor. At each cationic (Mg) concentration x, lattice constant decreases, while bulk modulus and band gap increase nonlinearly with increase in anionic (Se) concentration y. Again, nonlinear increase in lattice constant and band gap, while decrease in bulk modulus is observed with increase in cationic concentration x at each anionic concentrations y. Calculated band gap bowing for few ternary alloy systems are in good agreement with corresponding experimental data. The calculated contour maps for lattice constants and energy band gaps would be very useful for designing new quaternary alloys with desired optoelectronic properties. Optical properties of the said specimens within MgxZn1−xSeyTe1−y quaternary system show several interesting features. Composition dependence of each calculated zero-frequency limit shows opposite trend, while each calculated critical point shows similar trend of composition dependence of band gap. Finally, suitability of ZnTe and InAs as substrates for the growth of several zinc-blende MgxZn1−xSeyTe1−yquaternary alloys has been investigated.

Formation and Composition-Dependent Properties of Alloys of Cubic Halide Perovskites

Distinct shortcomings of individual halide perovskites for solar applications, such as restricted range of band gaps, propensity of ABX3 to decompose into AX + BX2, or oxidation of 2ABX3 into A2BX6, have led to the need to consider alloys of individual perovskites such as [FA,Cs][Pb,Sn][Br,I]3. This proposition creates a nontrivial material selection problem associated with a six-component structure, spanning a continuum of three sets of compositions (one for each sublattice) and requiring control of phase separation or ordering in each alloyed subfield. Not surprisingly, material and structure choices were made thus far mostly via trial-and-error explorations among a large number of arrangements. Here, we use ideas from solid-state theory of semiconductor alloys to analyze the behaviors of the canonical [FA,Cs][Pb,Sn]I3 alloy system, where FA is formamidinium. Density functional calculations utilizing specially constructed supercells are used to calculate the composition dependence of band gaps, energy o...

Compositional dependence of the band gap in Ga(NAsP) quantum well heterostructures

We present experimental and theoretical studies of the composition dependence of the direct band gap energy in Ga(NAsP)/GaP quantum well heterostructures grown on either (001) GaP- or Si-substrates. The theoretical description takes into account the band anti-crossing model for the conduction band as well as the modification of the valence subband structure due to the strain resulting from the pseudomorphic epitaxial growth on the respective substrate. The composition dependence of the direct band gap of Ga(NAsP) is obtained for a wide range of nitrogen and phosphorus contents relevant for laser applications on Si-substrate.

Ternary Alloyed ZnSexTe1–x Nanowires: Solution-Phase Synthesis and Band Gap Bowing

Ternary alloyed semiconductor nanostructures have attracted increasingly greater attention due to their unique physiochemical properties that may not be available in the parent binary systems. In this work, we report the solution–liquid–solid (SLS) growth of colloidal, uniform ZnSexTe1–x nanowires (NWs), the composition of which can be tuned over a wide range by manipulating the growth rate of multicomponent constituents. Two sets of ZnSexTe1–x NWs with high compositional homogeneities are synthesized by using zinc stearate (Zn(St)2) and diethyl zinc (Zn(Et)2) as the Zn precursor, respectively. The resultant NWs are systematically characterized with respect to the structure, composition, and optical band gap, and on the basis of these, the composition dependence of band gaps is extracted. Both sets of colloidal ZnSexTe1–x NWs are found to exhibit strong band bowing with the band gap minimum occurring at x = 0.30, which is consistent with the previously reported results based on ZnSexTe1–x bulk materials a...

Density functional and quasiparticle band-structure calculations forGaxAl1−xNandGaxIn1−xNalloys

We investigate the electronic structure of two wide-band-gap semiconductor alloys ${\mathrm{Ga}}_{x}{\mathrm{Al}}_{1\ensuremath{-}x}\mathrm{N}$ and ${\mathrm{Ga}}_{x}{\mathrm{In}}_{1\ensuremath{-}x}\mathrm{N},$ employing three different ab initio band-structure approaches. Local density calculations within density functional theory using conventional as well as self-interaction-corrected pseudopotentials and quasiparticle band-structure calculations are carried out. The stochastical alloy problem is treated within the virtual crystal approximation, as well as within a cluster expansion approximation. One main issue is the evaluation of the bowing of the composition dependence of the fundamental band gap. It turns out that the band-gap bowing for ${\mathrm{Ga}}_{x}{\mathrm{Al}}_{1\ensuremath{-}x}\mathrm{N}$ alloys is described reasonably well within the virtual crystal approximation. For ${\mathrm{Ga}}_{x}{\mathrm{In}}_{1\ensuremath{-}x}\mathrm{N},$ on the contrary, that approximation does not correctly describe the composition dependence of the band gap because it neglects significant local structural relaxations. These are taken into account in the cluster expansion approximation. Our results indicate that in both alloys the band gap exhibits a composition-dependent bowing function rather than a constant bowing parameter.

The anomalous composition dependence of the bandgap of GaAsN

In this work, the composition dependence of the fundamental bandgap of thin, pseudomorphic GaAs 1-x N x layers (0 < x ≤ 5%) on GaAs substrates is studied, using high resolution X-ray diffraction and optical transmission. A very large set of consistent experimental data is presented. The bowing parameter is allowed to vary as a function of N incorporation, and an empirical double exponential composition dependence is obtained. This expression accurately describes the measured bandgaps, and allows estimations for higher N-incorporations. The bowing parameter reaches 40 eV for very low N incorporations (x ≃ 0.1%), and strongly decreases with increasing N molar fraction. We estimate that the bowing parameter would reach a constant value of (7.5 ± 2.5)eV, as in an alloy, beyond our experimental range (x ≥ 8%). This seems to confirm the presence of three compositional regimes, the N-impurity region, the extended amalgamation region, and the alloy region.

CuxAg1–xGaS2 Solid Solutions

AbstractCuxAg1–xGaS2 large‐scale blocks were obtained by two‐temperature synthesis method with the following crystallization of the melt. It was established, that crystal lattice parameters are changed according with Vegard's law, and microhardness have an extremum on the base DTA measurements state diagram of AgGaS2CuGaS2 system was built up. The composition dependence of band gap has nonlinear behaviour.