xN Ternary Alloys Research Articles

Structural, Electronic, and Optical Properties of Wurtzite VxAl1−xN Alloys: A First-Principles Study

We present a comprehensive study on the structural, electronic, and optical properties of VxAl1−xN ternary alloys using first-principles calculations. Our investigations employ the full-potential linearized augmented-plane-wave (FP-LAPW) method within the density functional theory (DFT) framework. The impact of varying vanadium composition (x = 0, 0.25, 0.5, 0.75, 1) on the structural, electronic, and optical characteristics of wurtzite VxAl1−xN alloys is examined in detail. Our findings reveal a distinct nonlinear relationship between the lattice constant, bulk modulus, and the concentration of vanadium (x) in the VxAl1−xN alloys. An analysis of the electronic band structures and densities of states reveals a metallic behavior in the VxAl1−xN alloys, primarily driven by the V-d states near the Fermi energy. These results shed light on the electronic properties of the alloys, contributing to a deeper understanding of their potential for various applications. Furthermore, we calculate various optical properties, including the real and imaginary dielectric functions, refractive index, energy loss spectrum, and reflectivity. The obtained optical functions provide valuable insights into the optical behavior of the VxAl1−xN alloys. The results contribute to the fundamental knowledge of these materials and their potential applications in various fields.

Cathodoluminescence Spectroscopy in Graded InxGa1-xN.

InGaN materials are widely used in optoelectronic devices due to their excellent optical properties. Since the emission wavelength of the full-composition-graded InxGa1-xN films perfectly matches the solar spectrum, providing a full-spectrum response, this makes them suitable for the manufacturing of high-efficiency optoelectronic devices. It is extremely important to study the optical properties of materials, but there are very few studies of the luminescence of full-composition-graded InxGa1-xN ternary alloy. In this work, the optical properties of full-composition-graded InxGa1-xN films are studied by cathodoluminescence (CL). The CL spectra with multiple luminescence peaks in the range of 365-1000 nm were acquired in the cross-sectional and plan-view directions. The CL spectroscopy studies were carried out inside and outside of microplates formed under the indium droplets on the InGaN surface, which found that the intensity of the light emission peaks inside and outside of microplates differed significantly. Additionally, the paired defects structure is studied by using the spectroscopic method. A detailed CL spectroscopy study paves the way for the growth and device optimization of high-quality, full-composition-graded InxGa1-xN ternary alloy materials.

Behaviour of Raman B1 (high) mode and evaluation of crystalline quality in the InxGa1–xN alloys grown by RF-MBE

InxGa1–xN ternary alloys are very promising for a variety of applications. However, high-quality growth of InxGa1–xN alloys, particularly in the intermediate In composition range, is very difficult. This study reports on a systematic analysis of the Raman spectra from the InxGa1–xN alloys grown by radio-frequency molecular beam epitaxy (RF-MBE) for the whole In compositional range, particularly in the intermediate range of In composition. The B1 (high) mode, which is inherently Raman inactive is observed for the InxGa1–xN alloys grown by RF-MBE. The behaviour of Raman inactive B1 (high) mode is studied for the evaluation of InxGa1–xN quality, which is found to vary with the In composition and the temperature of growth. The crystallinity of the InxGa1–xN alloys can be assessed using B1 (high) mode’s relative signal intensity and full-width at half-maximum, which are well agreed with the reflection high energy electron diffraction and X-ray diffraction analyses. The optimum growth temperature for the InxGa1–xN alloys grown by RF-MBE in the intermediate range of In composition is also discussed.

Tuning emission in violet, blue, green and red in cubic GaN/InGaN/GaN quantum wells

Light emission in the three primary colors was achieved in cubic GaN/InGaN/GaN heterostructures grown by molecular beam epitaxy on MgO substrates in a single growth process. A heterostructure with four quantum wells with a width of 10nm was grown; this quantum wells width decrease the segregation effect of In. Photoluminescence emission produced four different emission signals: violet, blue, green-yellow and red. Thus, we were able to tune energy transitions in the visible spectrum modifying the In concentration in cubic InxGa1−xN ternary alloy.

Ductility behaviour of cubic titanium niobium nitride ternary alloy: a first-principles study

The ductility and hardness behaviour of NbxTi1−xN (x = 0, .25, .5, .75 and 1) ternary alloy has been studied. Bulk modulus, Young’s modulus, shear modulus, Poisson’s ratio and anisotropy energy have been calculated. Analysis of G/B and Cauchy’s pressure shows that TiN is brittle in nature in good agreement with other theoretical results. Systematic addition of Nb with TiN shows that Nb.75Ti.25N is ductile. The charge density plot shows weak directional contours that enclose Ti and N due to the ductile behaviour of the alloy, namely Nb.75Ti.25N. The estimated hardness of Nb.75Ti.25N is 19.78 GPa, which is 70 % of hardness value of TiN (29.4 GPa) and thus addition of niobium enhances the ductility of TiN. The Debye temperature of the present alloy system is also reported.

Concentration and temperature dependence of the energy gap in some binary and alloy semiconductors

Concentration dependence of the energy gap Eg(x) of In1−xGaxAs, InP1−xAsx, GaxAl1−xAs, GaPxAs1−x and AgGaxIn1−xSe2 alloy semiconductors, and temperature dependence of the energy gap Eg(T) of GaS, GaSe, GaTe, SnS and SnSe2 binary semiconductors have been studied. Both the concentration and temperature dependence of the energy gap Eg(x, T) of AlxGa1−xN ternary alloy, and concentrations dependence of the energy gap Eg(x, y) of In1−xGaxAs1−yPy quaternary alloy semiconductor have also been investigated. Simple relations have been proposed for the calculation of Eg(x), Eg(T), Eg(x, T) and Eg(x, y) for various binary and alloys semiconductors. The average percentage deviation of all proposed relations has been estimated and found to be better than the earlier correlations. The calculated values are compared with the available experimental values and the values reported by different workers. A fairly good agreement has been obtained between them.

Bulk lattice parameter and band gap of cubic InXGa1−XN (001) alloys on MgO (100) substrates

InxGa1−xN (001) ternary alloys were grown on GaN/MgO (100) substrates in a plasma assisted molecular beam epitaxy system. We determined the in-plane [001] and in-growth [110] lattice parameters, as well as the bulk lattice parameter of the alloys for different In concentrations by high resolution X-ray diffraction. The In concentration was determined assuming Vegard׳s law for the alloy lattice parameter. The optical energy gap of InxGa1−xN has been determined by transmittance measurements from absorption edges for several In concentrations. Our results show that the alloys have a direct band gap for all In concentrations and a bowing parameter b=1.84.

The electronic and optical properties of InGaN-based solar cells alloys: First-principles investigations via mBJLDA approach

First-principles calculations of the electronic and optical properties of the bulk In x Ga1 − x N alloys are simulated within the framework of full-potential linearized augmented plane-wave (FP-LAPW) method. To this end, a sufficiently adequate approach, namely modified Becke-Johnson (mBJLDA) exchange correlation potential is employed for calculating the energy band gap and optical absorption of InGaN-based solar cells systems. The quantities such as the energy gap, density of states, imaginary part of dielectric function, refractive index and absorption coefficient are determined for the bulk In x Ga1−x N alloys, in the composition range from x = 0 to x = 1. It is found that the indium composition robustly controls the variation of band gap. From the examination of the density of states and optical absorption of In x Ga1−x N ternary alloys, the energy gaps are significantly reduced for largest In concentration. The computed band gaps vary nonlinearly with the composition x. It is also surmised that the significant variation in the band gaps elaborated via the experimental crystalline growth process, is originated by altering the In composition. Interestingly, it is worthwhile to perform InGaN solar cells alloys with improved efficiencies, because of their entire energy gap variation from 0.7 to 3.3 eV.

Structural and electronic properties of ScxAl1−xN: First principles study

The structural and electronic properties of ScxAl1−xN ternary semiconductor alloys are investigated in the rocksalt, zinc blend and wurtzite structures using the full potential linear muffin tin orbitals (FP-LMTO) method. The local density approximation (LDA) was used for the exchange and correlation energy density functional. In particular, the lattice constant, bulk modulus and band gap energies of ScN and AlN compounds and their ternary alloys ScxAl1−xN are calculated in rocksalt, zinc blend and wurtzite structures and discussed. A linear relationship has obtained for equilibrium lattice constants versus Sc concentration for rocksalt and zinc blend structures. The band gap is decreased with the increasing of Sc concentration in the rocksalt phase. For ZB-ScxAl1−xN, the band gap is the largest one at x=0.25 and changes from indirect to direct when x is more than 0.25.

Effect of the growth temperature on the properties of AlxGal−xN epilayers grown by HVPE

Growth of the AlxGa1−xN ternary alloy using AlCl3 and GaCl gases on sapphire substrate by hydride vapor phase epitaxy (HVPE) is presented in this study. AlxGa1−xN epilayers were grown directly on sapphire substrate. To investigate the effect of growth temperature, we varied temperature from 1050 to 1090°C at intervals of 20°C. Some compositional non-uniformity was observed on the epilayer grown at 1050°C from the results of UV–vis spectrophotometry, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Such a compositional non-uniformity disappeared with the increase of growth temperature and it was confirmed with the existence of Ga-rich islands shown by electron probe microanalysis (EPMA) compositional mapping. In addition, other characteristics such as surface roughness and crystallinity also improved with the increase of growth temperature and showed best results at 1090°C. The Al composition of epilayer grown at 1090°C was around 30%.

Raman Scattering Study of InxGa1−xN Alloys with Low Indium Compositions

InxGa1−xN alloys with low indium composition x in the range 0.13 ≤ x ≤ 0.23 are systematically studied mainly based on a Raman scattering technique. Scanning electron microscopy and x-ray diffraction results show that our samples can be divided into two groups: pseudomorphic (0.13 ≤ x ≤ 0.16) and relaxed (0.18 ≤ x ≤ 0.23). The prominent enhancement of A1 longitudinal-optical (LO) mode is found with 325 nm laser excitation. For pseudomorphic samples, the frequencies of A1 (LO) phonons agree well with the theoretical predictions, which verifies that the samples are fully strained. For relaxed InxGa1−xN samples, a linear dependence of the A1 (LO) mode frequency is obtained: Ω0(x) = (740.8 ± 3.3) − (143.1 ± 16.0)x, which is the evidence of one-mode behavior in InxGa1−xN ternary alloys. Residual strains in these partially relaxed samples are also evaluated.

X‐ray diffraction studies of AlxGa1−xN (0≤x≤1) ternary alloys grown on sapphire substrate

PurposeThe purpose of this paper is to report the structural properties of AlxGa1−xN (0≤x≤1) grown on sapphire substrate by means of X‐ray diffraction (XRD) technique. The main purpose of this work was to investigate the effects of Al(x) composition to the structural and microstructural properties of AlxGa1−xN ternary alloy such as the crystalline quality, crystalline structure and lattice constant c.Design/methodology/approachAlxGa1−xN thin films with wurtzite structure in the composition range of 0≤x≤1 are used in this study. The compositions of the samples are calculated using Vegard's law and verified by energy dispersive X‐ray analysis. The samples are then characterized by means of XRD rocking curve (RC) and phase analysis.FindingsInvestigation revealed that the full width half maximum (FWHM) of RC increase with the increase x value. This indicates that the crystalline quality of the samples deteriorate with the increase of Al compositions. The best fit of the non‐linear interpolation of the FWHM of the (002) diffraction RC data suggested that a maximum disorder should be expected in this mixed crystals system when the composition x≈45 percent.Originality/valueThis paper provides valuable information on the effect of Al compositions to the structural characteristics of AlxGa1−xN alloy system. The availability of information about maximum disorder of Al composition in AlxGa1−xN (0≤x≤1) alloy system provides useful reference in device fabrications where researchers are able to choose correct alloy composition in order to fabricate good quality devices.

Theoretical studies of surface phonon polariton in wurtzite AlInN ternary alloy

In this study, we report the surface phonon polariton (SPP) characteristics of wurtzite structure aluminium indium nitride (AlxIn1−xN) ternary alloys over the whole Al composition range. An anisotropic model is used to simulate the surface polariton (SP) dispersion curves of the AlxIn1−xN ternary alloys. The characteristics of these dispersion curves are discussed in detail and the effects of the composition dependence of the AlxIn1−xN on the SPs are illustrated and explained. Moreover, the relevant experimental information from the attenuated total reflection (ATR) method is also presented, namely, the corresponding ATR spectra are simulated based on the standard matrix formulation. Through this study, it has been found that the SPP mode of the wurtzite AlxIn1−xN exhibits mixed-mode behaviour.

Anomalous Behaviors of Cubic GaInN Ternary Alloys

The electronic and optical properties of cubic Ga_1-xIn_xN ternary alloys are theoretically investigated using the sp3s* tight-binding model, with the inclusion of spin-orbit interaction, versus composition and valence-band offset (VBO), stimulating the lattice-relaxation effects. Usually, the bowing of the band-gap energy in the common-anion ternary alloys should be vanishingly small as far as the virtual-crystal approximation remains valid. In contrary to this, the present alloys are shown to possess three unusual characteristics: (i) They possess rather strong bowing character with b > 2.0 eV; (ii) the bowing parameter is composition dependent b = b(x); and (iii) the Stokes shift between emission and absorption is so large that can even reach 200 meV when x ≈ 0.5. Two reasons are claimed to cause such behaviors; namely: the strong electro-negativity of nitrogen atoms and the large lattice relaxation as being induced by the large lattice-mismatch between the two constituents (GaN and InN). The favorable comparison with the available experimental data corroborates the above claims.

Huge binding energy of localized biexcitons in Al-rich AlxGa1−xN ternary alloys

Excitonic optical properties of Al-rich AlxGa1−xN ternary alloy epitaxial layers have been studied by means of photoluminescence excitation spectroscopy. On the basis of the energy separation between exciton resonance and two-photon biexciton resonance, the binding energy of biexcitons was estimated to be 56±5 and 48±5 meV for the sample with x=0.81 and 0.89, respectively. The biexciton binding energy of 56 meV was approximately three times as large as the biexciton binding energy of 19 meV in AlN. The large enhancement of the biexciton binding energy resulted from the strong localization of biexcitons due to alloy disorder.

Temperature dependence of localized exciton transitions in AlGaN ternary alloy epitaxial layers

The optical properties of Ga-rich AlxGa1−xN (x=0.019, 0.038, 0.057, 0.077, and 0.092) ternary alloy epitaxial layers have been studied by means of temperature-dependent photoluminescence (PL) and time-resolved PL spectroscopy. The luminescence intensity of excitons in five epitaxial layers indicated a thermal quenching process with two activation energies. The two quenching activation energies were attributed to the delocalization of excitons and thermal dissociation of excitons. Anomalous temperature dependence of the PL peak energy was also observed in the epitaxial layers, which enabled the evaluation of the localization energy of the excitons. The localization energy increased as the 1.7th power of the PL linewidth, which reflected a broadening of the density of localized exciton states. In addition, the luminescence decay of the localized excitons for the five epitaxial layers became longer with decreasing emission energy. These observations suggest that the decay of excitons is caused not only by radiative recombination, but also by transfer to lower energy states.

Calculations of electronic structure, elastic properties for YxGa1−xN and band offsets of YxGa1−xN/ScyGa1−yN heterointerfaces

Using the pseudopotential scheme under the virtual crystal approximation combined with the Harrison bond-orbital model, we report a theoretical investigation of the electronic and elastic properties of YxGa1−xN ternary alloys in the zinc-blende structure. Besides, band offsets calculations for pseudomorphically strained YxGa1−xN/ScyGa1−yN interfaces have been performed on the basis of the model solid theory. Our results agree generally well with the available experimental and previously published theoretical data. The composition dependence of the selected features of YxGa1−xN such as energy band gaps, effective masses, elastic constants, bulk modulus, shear modulus, internal strain parameter, and valence and conduction band offsets has been examined. To the author's best knowledge, there had been no reported work on these properties for the material under load.

Growth and properties of Al-rich InxAl1−xN ternary alloy grown on GaN template by metalorganic chemical vapour deposition

An Al-rich InxAl1−xN ternary alloy was grown on a GaN template by metal–organic chemical vapour deposition (MOCVD). The GaN template was fabricated on a c-plane sapphire with a low temperature GaN nucleation layer. The growth of the 300 nm thick InxAl1−xN layer was carried out under various growth temperatures and pressures. The surface morphology and the InN molar fraction of the InxAl1−xN layer were assessed by using atomic force microscopy (AFM) and high resolution x-ray diffraction, respectively. The AFM surface images of the InxAl1−xN ternary alloy exhibited quantum dot-like grains caused by the 3D island growth mode. The grains, however, disappeared rapidly by increasing diffusion length and mobility of the Al adatoms with increasing growth temperature and the full width at half maximum value of ternary peaks in HR-XRD decreased with decreasing growth pressure. The MOCVD growth condition with the increased growth temperature and decreased growth pressure would be effective to grow the InxAl1−xN ternary alloy with a smooth surface and improved quality. The optical band edge of InxAl1−xN ternary alloys was estimated by optical absorbance and, based on the results of HR-XRD and optical absorbance measurements, we obtained the bowing parameter of the InxAl1−xN ternary alloy at b = 5.3 eV, which was slightly larger than that of previous reports.

Population dynamics of localized biexcitons in AlxGa1−xN ternary alloys

Dynamical behavior of localized biexcitons in Ga-rich AlxGa1−xN ternary alloys has been studied by means of time-resolved luminescence spectroscopy. The time-dependent luminescence was analyzed using rate equations which were modified by considering the localization times of both the biexcitons and single excitons individually. The localization times of both biexcitons and single excitons became longer with increasing aluminum composition. On the other hand, the formation time of biexcitons from single excitons remained nearly unchanged. This observation indicated that the formation rate of biexcitons in the ternary alloys was independent of the localization depth of single excitons.

Femtosecond carrier dynamics of InxGa1−xN thin films grown on GaN (0001): Effect of carrier-defect scattering

Ultrafast carrier dynamics in ultrathin InxGa1−xN ternary alloys were investigated in detail, using femtosecond transient differential optical absorption measurements. Measurements were performed with probing wavelengths above and below the band edge of the materials. Furthermore, we performed a structural characterization by x-ray diffraction reciprocal space maps and we found that the alloys with the higher InN mole fraction (x=0.89 and x=0.43) present large lattice mismatch-strain relaxation whereas the lower InN content alloy was fully coherent with the underlying GaN (0001) layer. Our analysis showed that the observed nonradiative carrier dynamics was strongly related with the carrier-defect scattering of the materials. Our measurements in conjunction with the numerical analysis showed that when we excite these alloys with ultrashort laser pulses the background carrier concentration for In-rich InGaN samples participates to the photoexcited carrier relaxation process via carrier momentum scattering. For the higher InN content alloys (x=0.89 and 0.43) the relaxation times were short (0.4–1.4ps) whereas for the full strained alloy (x=0.07) a slower nonradiative relaxation time (∼25ps) was observed. Finally, the energy loss rate of this material (2.05±0.10meV∕fs) as well as the optical phonon lifetime (44±2fs) were extracted.