xP Alloys Research Articles

Electronic, optical, and mechanical properties of AlxIn1−xP alloys under temperature and pressure

In this work, the optoelectronic and mechanical properties of AlxIn1−xP combinations in the zinc-blende structure were studied for different Al concentrations. The energy band gaps left( {{text{E}}_{{text{g}}}^{{text{L}}} ,,{text{E}}_{{text{g}}}^{Gamma } ,,{text{E}}_{{text{g}}}^{{text{X}}} } right), refractive index (n), high frequency and static dielectric constants (ɛ∞, ɛo), elastic parameters (C11, C12, C44) were investigated. Other mechanical properties such as bulk (Bu), shear (Cs), Young’s (Y0) moduli, Poisson ratio (σ), linear compressibility (C_{o} ), Cauchy (C_{a} ) ratio, isotropy factor (A), bond stretching parameter (alpha ,), bond-bending force parameter (beta ,), internal-strain parameter (xi ), and the transverse effective charge (e_{T}^{*} ) were calculated. Also, the temperature and pressure dependences of these properties were studied. Our estimations were made with the empirical pseudo-potential method combined with the virtual crystal approximation incorporated the compositional disorder impact. There was a reasonable agreement between our determined outcomes and the accessible experimental values for the binary materials AlP and InP which give help for the consequences of the ternary combinations.

Si-matched BxGa1−xP grown via hybrid solid- and gas-source molecular beam epitaxy

The growth of BxGa1−xP alloys by hybrid solid/gas-source molecular beam epitaxy, with B supplied via the BCl3 gas precursor, is demonstrated. Compositional control ranging from pure GaP to B0.045Ga0.955P has thus far been achieved. Slightly tensile-strained B0.031Ga0.969P grown on nearly pseudomorphic, compressively strained GaP/Si was used to produce an effectively strain-free (0.06% tensile misfit at growth temperature) 160 nm total III–V thickness BxGa1−xP/Si virtual substrate with a threading dislocation density of <3 × 105 cm−2, at least 4× lower than comparable GaP/Si control samples. Cross-sectional transmission electron microscopy reveals that subsequent GaP overgrowth undergoes epilayer relaxation via dislocation introduction and glide at the upper GaP/B0.031Ga0.969P interface, rather than the lower GaP/Si interface, confirming the strain-balanced nature of the B0.031Ga0.969P/GaP/Si structure and its potential use as a III–V virtual substrate.

First Principles Study on Electronic Structure and Optical Properties of Ternary Semiconductor InxAl1 –xP Alloys

The elastic, electronic and optical properties of the indium doped AlP, have been investigated by the first-principle calculations within the framework of the density functional theory (DFT). Our calculated lattice constants and bulk moduli for AlP and InP are in good agreement with the available theoretical and experimental data. The lattice constants increase while the bulk modulus decreases with In concentration increasing. The elastic constants Cij of InxAl1 –xP alloys have been calculated for the first time. Result shows that with the increase of indium concentration, the band gap of InxAl1 –xP decreases and varies from indirect band gap to direct band gap; the absorption band edge and the absorption peak move to low energy side; the static reflectivity increases. With the increasing of the incident photon energy, InxAl1 –xP shows metal reflective properties in certain energy range. With the increasing of Indium concentration, static dielectric constant increases and the intersection of dielectric function and the x-axis move towards low energy side; the peak of energy loss function move to high energy side and the peak value reduces.

Experimental studies of the effects of atomic ordering in epitaxial Ga x In1 – x P alloys on their optical properties

The properties of epitaxial Ga x In1 – x P alloys with an ordered arrangement of atoms in the crystal lattice are studied by a number of spectroscopic methods. The alloys are grown by metal-organic chemical vapor deposition onto single-crystal GaAs(100) substrates. It is shown that, under conditions of the coherent growth of an ordered Ga x In1 – x P alloy on a GaAs(100) substrate, atomic ordering results in radical modifications of the optical properties of the semiconductor compared to the properties of disordered alloys. Among these modifications are a decrease in the band gap and an increase in the luminescence intensity. From the data of dispersion analysis of the infrared dispersion spectra and from ultraviolet spectroscopy data obtained in the transmittance–reflection mode of measurements, the basic optical characteristics, specifically, the dispersion of the refractive index and the high-frequency permittivity of Ga x In1 – x P alloys with ordering are determined. All of the experimental data are in good agreement with the developed theoretical concepts.

Direct bandgap photoluminescence from n-type indirect GaInP alloys

This work studies Te doping effects on the direct bandgap photoluminescence (PL) of indirect GaxIn1−xP alloys (0.72≤x≤0.74). The temperature-dependent PL shows that the energy difference between direct Γ valley and indirect X valleys is reduced due to the bandgap narrowing (BGN) effect, and the direct band transition gradually dominates the PL spectra as temperature increases. Carrier thermalization has been observed for Te-doped GaxIn1−xP samples, as integrated PL intensity increases with increasing temperature from 175 to 300 K. The activation energy for carrier thermalization is reduced as doping concentration increases. Both BGN effect and carrier thermalization contribute to the carrier injection into the Γ valley. As a result, the direct band transition is enhanced in the Te-doped indirect GaxIn1−xP alloys. Therefore, the PL intensity of the Ga0.74In0.26P sample with active doping concentration of 9×1017 cm−3 is increased by five times compared with that of a nominally undoped sample. It is also found that the PL intensity is degraded significantly when the doping concentration is increased to 5×1018 cm−3. From cross-section transmission electron microscopy, no large dopant clusters or other extended defects were found contributing to this degradation.

First Principles Prediction of Structural, Electronic and Optical Properties of Zinc Blende InxGa1–xP Alloys

First Principles Prediction of Structural, Electronic and Optical Properties of Zinc Blende InxGa1–xP Alloys

Ion-implantation-induced amorphization of InxGa1−xP alloys as functions of stoichiometry and temperature

Rutherford Backscattering Spectrometry/Channeling and Extended X-ray Absorption Fine Structure measurements have been combined to investigate the amorphization of InxGa1−xP alloys at 15 and 300 K for selected stoichiometries representative of the entire stoichiometric range. The amorphization kinetics differs considerably for the two temperatures: at 15 K, the amorphization kinetics of InxGa1−xP is intermediate between the two binary extremes while at 300 K, InxGa1−xP is more easily amorphized than both InP and GaP. Direct impact and stimulated amorphization both contribute to the amorphization process at 15 K. Dynamic annealing via thermally induced Frenkel pair recombination reduces the influence of direct impact amorphization at 300 K such that the stimulated amorphization is dominant. At this temperature, stimulated amorphization in ternary InxGa1−xP alloys is supported by the structural disorder inherent from the bimodal bond length distribution.

Optical and electronic properties of BxAl1−xP alloys: A first principles study

The electronic, optical and thermodynamic properties of boron alloying aluminum phosphide (BxAl1−xP) ternary mixed crystal are studied by the first-principle calculations within the framework of the density functional theory (DFT). Our calculated lattice constants and bulk moduli for AlP and BP are in good agreement with the available theoretical and experimental data. The lattice constants decrease while the bulk modulus increases with B concentration increasing. The calculated band structure for the concentrations x=0.25, 0.50, and 0.75 are direct gap semiconductors. The density of states and optical constants such as complex dielectric function, extinction coefficient, refractive index and absorption coefficient are also calculated and analyzed in detail. Moreover, the thermodynamic stability of these alloys is investigated by the calculated T−x phase diagram.

An ab initio study of the “direct–indirect band gap” transition in AlxIn1−xP alloys

The composition-induced “direct–indirect” band gap transition in the AlxIn1−xP alloys was studied theoretically. Two different approaches – virtual crystal approximation and supercell-based calculations, both in the general gradient and local density approximations – were used to model the influence of the chemical composition on the structural and electronic properties of the AlxIn1−xP system in the whole range of Al concentration x from 0 to 1. The band gap crossover from the direct to indirect band gap was shown to take place at x=0.406, in excellent agreement with the experimental result x=0.408 of Beaton et al. It was also demonstrated that the supercell-based calculations are better suited to describe variation of the composition-driven structural properties, whereas the virtual crystal approximation is better to be employed for the analysis of the electronic properties of the title system.

Energy band structure calculations of GaxIn1−xP alloys under the influence of temperature and pressure

This work is concerned with the dependence of the electronic energy band structures for GaxIn1−xP alloys on temperature and pressure. The calculations are based on local empirical pseudo-potential method (EPM) coupled with the virtual crystal approximation (VCA) which incorporates compositional disorder as an effective potential. The direct and indirect energy band gaps of the considered alloys have been determined over entire composition parameter, x from 0 to 1, temperature from T=0K to 500K and pressure from P=0Kbar to 120Kbar. In addition, the refractive index and dielectric constant of the considered alloys under the effect of composition, temperature and pressure have also been studied. The ternary alloys GaxIn1−xP is bordered by two binary compounds GaP and InP which have been studied recently by our group. Comparison of the calculated results with the experimental and published data showed good agreement.

Band structure properties of novel BxGa1−xP alloys for silicon integration

We have grown and investigated the band-structure properties of novel III-V alloys based upon BxGa1−xP. These layers are utilized as strain-compensating layers for the lattice-matched integration of novel direct bandgap Ga(NAsP) quantum well lasers on silicon. Experimental and theoretical studies reveal the dependence of the direct and indirect band gaps for strained BxGa1−xP layers grown on silicon as a function of Boron composition from which we derive the properties of free-standing BxGa1−xP. For Boron fractions up to 6%, we find that the bowing parameter for the lowest (indirect) band gap is − 6.2 ± 0.2 eV. High crystalline quality and promising optical material properties are demonstrated and applied to monolithically integrated Ga(NAsP)/(BGa)P multi-quantum well heterostructures on (001) silicon substrates. Our results show that novel (BGa)P layers are suitable for strain compensation purposes, which pave the way towards a commercial solution for the monolithic integration of long term stable laser diodes on silicon substrates.

Ordering induced direct-indirect transformation in unstrained GaxIn1−xP for 0.76≤x≤0.78

Ga x In 1 − x P alloys grown by metalorganic vapor phase epitaxy (MOVPE) are known to exhibit spontaneous long-range ordering that results in a modification of the alloy electronic band structure. Using time resolved and time integrated photoluminescence studies at 9 K, we demonstrate that the change in alloy ordering in GaxIn1−xP alloys can transform the conduction to valence band optical transition from direct to indirect for a given Ga concentration. This finding may enable sequential growth of alternate layers of high bandgap direct and indirect semiconductor alloys with similar lattice constants, opening various possibilities for device applications.

Disorder effects on electronic and optical properties of the ternary GaxIn1−xP (x = 0.25, 0.50, and 0.75) alloy

AbstractWe have performed first‐principles calculations for the electronic and optical properties of GaxIn1−xP alloys for compositions x = 25, 50, and 75%. The effects of Ga composition on the electronic density of states, dielectric functions, and pressure coefficients are discussed in detail using a simple cubic structure and a special quasi‐random structure. Effective masses are calculated along the Γ(000) symmetry point. Overall, the calculated properties are in agreement with the available experimental data. Our calculations show that the direct band gap and the electron effective masses vary nonlinearly with concentration x.

CuPt ordering in high bandgap GaxIn1−xP alloys on relaxed GaAsP step grades

We have fabricated a series of GaxIn1−xP samples over the compositional range 0.51<x<0.76 on GaAs substrates. The samples were prepared by first growing a thick step-graded layer of GaAs1−yPy to bridge the lattice misfit between the GaxIn1−xP layers and the GaAs substrate. The order parameter was tuned using a dilute antimony surfactant during growth. The composition, strain, and order parameter of each sample were characterized by x-ray diffraction, and the bandgap was measured by photoluminescence. We find good agreement between the experimentally measured bandgaps and theoretically modeled curves.

High-efficiency dual-junction GaInP/GaAs tandem solar cells obtained by the method of MOCVD

Monolithic dual-junction GaInP/GaAs solar cells grown by the MOCVD method were studied. The conditions of the growth of ternary Ga x In1−x P and Al x In1−x P alloys lattice-matched to GaAs are optimized. Technology for fabrication of a tunneling diode with a high peak current density of 207 A/cm2 on the basis of heavily doped n ++-GaAs:Si and p ++-AlGaAs:C layers is developed. Cascade GaInP/GaAs solar cells obtained as a result of relevant studies featuring a good efficiency of the solar-energy conversion both for space and terrestrial applications. The maximum value of the GaInP/GaAs solar-cell efficiency was 30.03% (at AM1.5D, 40 suns).

Optical properties of bulk and epitaxial unordered GaxIn1−x P semiconductor alloys

The electron band structure of GaxIn1−xP bulk solid solutions was calculated by the local model pseudopotential method taking into account lattice mismatch. The resulting local strain of the lattice was taken into account in calculations of effective mass and deformation potential. The main optical characteristics of GaxIn1−xP alloys can be explained by the presence of internal local strains and antisite defects. In comparison with bulk samples, the concentration dependences of the spectral peaks E1 and E1+Δ1 in pseudomorphic thin films were found to be more sensitive than the fundamental absorption edge E0 to deformations caused by the substrate.

Optical properties of AlxGa1−xP (0⩽x⩽0.52) alloys

We report optical properties of AlxGa1−xP (0⩽x⩽0.52) alloys grown by gas source molecular-beam epitaxy on S-doped GaP(001) substrates. Room-temperature pseudodielectric function spectra from 1.5 to 6.0 eV were obtained by spectroscopic ellipsometry. By applying the parabolic-band critical point model to numerically calculated second energy derivatives of these spectra, we obtained accurate room-temperature values of the E1, E0′, E2, and E2′ critical point energies and their dependence on composition x.

Optical characterization of disordered InxGa1−xP alloys

We present results on the optical characterization of InxGa1−xP layers grown by atomic layer molecular beam epitaxy on GaAs (001) substrates at a growth temperature of 420 °C. Our results show that the optical characteristics of these layers, which do not show ordering effects, are strongly dependent on surface stoichiometry during growth. In this way, we can obtain either highly homogeneous alloys with a predictable band-gap energy or layers with optical properties indicative of spatial localization effects, like an anomalous behavior of photoluminescence peak energy with temperature and a large shift between the emission energy and absorption edge.

Vapor-solid distribution in In 1− xGa xAs and In 1− xGa xP alloys grown by atomic layer epitaxy

A chemical equilibrium model is applied to the halogen transport atomic layer epitaxy (ALE) growth of In 1− x Ga x As and In 1− x Ga x P alloys. The alloy composition is computed thermodynamically as a function of the input partial pressure ratio at various temperatures. The thermodynamically predicted composition of the alloys is compared with experimental data reported previously. It is shown that the alloy composition of layers grown by halogen transport ALE can be well explained by the equilibrium model.

A quantum statistical theory of linewidths of radiative transitions due to compositional disordering in semiconductor alloys

A quantum statistical formalism has been developed for the excitonic luminescence linewidths and line shapes in semiconductor binary alloys due to band-gap fluctuations caused by the random distributions of the alloy components in an applied magnetic field. The virtual crystal approximation is used to estimate the local band-gap variations. The shifts of the excitonic transition energy due to the band-gap fluctuations are obtained using the first-order perturbation theory. A Gaussian line shape is obtained for the excitonic transition using standard statistical techniques. This formalism is applied to calculate the linewidths and line shapes associated with the ground-state excitonic transition as a function of alloy composition and magnetic-field strength in AlxGa1−xAs and InxGa1−xP alloys. The resulting linewidths and line shapes are in good agreement with the available low-temperature photoluminescence data; however, the calculated linewidths are consistently smaller than the measured values. The possible mechanisms responsible for this discrepancy are discussed. A comparison of excitonic linewidths obtained from the present theory with those calculated earlier is also presented.