Electronic and structural properties of GaN by the full-potential linear muffin-tin orbitals method: The role of the d electrons

Sonochemical Assisted Solvothermal Synthesis of Gallium Oxynitride Nanosheets and their Solar-Driven Photoelectrochemical Water-Splitting Applications

Gallium oxynitride (GaON) nanosheets for photoelectrochemical (PEC) analysis are synthesized via direct solvothermal approach. Their FE-SEM revealed nanosheets morphology of GaON prepared at a reaction time of 24 hours at 180 °C. The elemental composition and mapping of Ga, O and N are carried out through electron dispersive X-ray spectroscopy (EDX). The cubic structure of GaON nanosheets is elucidated by X-ray diffraction (XRD)analysis. The X-ray Photoelectron Spectroscopy (XPS) further confirms Ga, O and N in their respective ratios and states. The optical properties of GaON nanosheets are evaluated via UV-Visible, Photoluminescence (PL) and Raman spectroscopy’s. The band gap energy of ~1.9 eV is calculated from both absorption and diffused reflectance spectroscopy’s which showed stronger p-d repulsions in the Ga (3d) and N (2p) orbitals. This effect and chemical nitridation caused upward shift of valence band and band gap reduction. The GaON nanosheets are investigated for PEC studies in a standard three electrode system under 1 Sun irradiation in 0.5 M Na₂SO₄. The photocurrent generation, oxidation and reduction reactions during the measurements are observed by Chronoampereometry, linear sweep Voltametry (LSV) and Cyclic Voltametry (CV) respectively. Henceforward, these GaON nanosheets can be used as potential photocatalyts for solar water splitting.

Thermoelectric properties of highly-mismatched alloys of GaNxAs1−x from first- to second-principles methods: energy conversion

The transport properties of GaN_xAs_1−x (x = 0.0, 0.25, 0.5, 0.75 and 1.0) alloys are investigated using the semi-classical Boltzmann theory as implemented in the BoltzTraP code.

Computational study on the mechanism and enantioselectivity of Rh2(S-PTAD)4 catalyzed asymmetric [4+3] cycloaddition between vinylcarbenoids and dienes

In this paper, the mechanism of asymmetric [4+3] cycloaddition between a vinylcarbenoid and a diene to form cycloheptadiene has been studied using a two-layer ONIOM methodology consisting of density functional theory and semiempirical PM6.

Stability of the bulk phase of layered ZnO

Recently a novel phase of ZnO has been synthesized which is analogous to α-boron nitride, although more three dimensional, and consists of planar hexagonal sheets of ZnO. Examining the dynamic stability of the structure, we find unstable phonon modes over a considerable part of the Brillouin zone. Local-density approximation (LDA) and generalized gradient approximation level calculations have usually been able to predict the structural stability of s-p bonded systems. The failure in the present case is a surprise and is traced to the self-interaction error which incorrectly locates the localized Zn d states in the valence band of ZnO. Correcting for this with a Hubbard-like U on the Zn d states, the optimized structure is predicted to be stable. This highlights the fact that the large bond length contraction that one finds in going from sp(3)- to sp(2)-type bonding results in an increased necessity to correct for self-interaction errors.

Electronic Structure of Diamond, Silicon Carbide, and the Group-III Nitrides

This paper describes the trends in the electronic structure of diamond, silicon carbide, the group-Ill nitrides and some related materials. The relationships between the electronic band structures in the zincblende and wurtzite structures are adressed. For SiC, the discussion is extended to other poly types. The trends with ionicity and atomic number are explained. The purpose of this discussion is to help identify the similarities and differences between the various classes of wide bandgap semiconductors. The strain effects on the band structure are discussed and calculated elastic constants are given for SiC, GaN and AlN. Spectroscopie probes of the band structure such as pholoemission and UV-refiectivity are discussed for GaN and SiC. Materials with the formula II-IV-2 are proposed to be an interesting complement to the III-N's. In particular, BeCN2 is a direct gap semiconductor with elastic properties close to those of diamond and may also be useful as a bufferlayer for diamond growth.

Hydrogen, Acceptors, and H-Acceptor Complexes in GaN

We present ab-initio calculations on energetics and geometries of atomic hydrogen, of several candidate acceptors, and of H-acceptor complexes in wurtzite GaN For the H-Mg complex in Mg-doped GaN, we calculate the vibrational frequencies of H. Hydrogen is found to be a negative-U center. H-acceptor complex formation is always exothermic. Substitutional Be has a low formation energy and a shallow impurity level, which makes it a good candidate for p-doping in MBE growth. CN appears not to be shallow. Atomic hydrogen incorporation in undoped GaN is disfavored in an H2 atmosphere; it becomes favorable in p and n-type conditions in atomic H environments.

Native Defects in Wurtzite GaN And AlN

The results of an extensive theoretical study of native defects in GaN and of vacancies in AlN are presented. We have considered cation and anion vacancies, antisites, and intersti-tials. The computations were carried out using quantum molecular dynamics, in supercells containing 72 atoms. Due to the wide gap of nitrides, the formation energies of defects depend strongly on the position of the Fermi level. The N vacancy in GaN introduces a shallow donor level that may be responsible for the n-type character of as-grown GaN.Other defects introduce deep states in the gap, with strongly localized wave functions.

Structural and Electronic Properties of AlN, GaN And InN, and Band Offsets at AlN/GaN (1010) and (0001) Interfaces

Ab initio local-density-functional calculations are presented for bulk A1N, GaN, and InN in the wurtzite, zincblende, and rocksalt structures. Structural transition pressures and deformation potentials of electronic gaps are investigated. In addition, we study the band offset at the polar (0001) and non-polar (1010) AIN/GaN interfaces. Within AIN-on-GaN epitaxial conditions, we obtain valence-band offset values close to 0.7 eV for both interfaces. From the macroscopic field appearing along the growth direction of the polar interface (tentatively attributed to AIN macroscopic polarization), an estimate of the macroscopic dielectric constant of GaN is extracted. All calculations employed conjugate-gradient total-energy minimizations, ultrasoft pseudopotentials, and plane waves at 25 Ryd cutoff.

Native Defects and Impurities in Cubic and Wurtzite Gan

Using state-of-the-art total energy calculations we investigate defect formation energies and electronic structure for native defects in wurtzite and cubic GaN.The defect formation energies and electronic structures are very similar in both structures. The main difference is a split in the p-like defect states in wurtzite GaN, which are degenerate in cubic GaN.|The role of the Ga 3d electrons on the chemical bonding in GaN is discussed in detail. We explain why the deep lying Ga 3d electrons have a remarkably strong influence on defect formation energies and atomic relaxation for some of the defects.

Offsets and Polarization at Strained AlN/GaN Polar Interfaces

The strain induced by lattice mismatch at the interface is responsible for the different value of the band discontinuities observed recently for the AlN/GaN (AlN on GaN) and the GaN/AlN (GaN on AlN) polar (0001) interface. We present a first-principles calculation of valence band offsets, interface dipoles, strain-induced piezoelectric fields, relaxed geometric structure, and formation energies. Our results confirm the existence of a large forward-backward asymmetry for this interface.

Atomistic modeling of III-V nitrides: modified embedded-atom method interatomic potentials for GaN, InN and Ga(1-x)In(x)N

Modified embedded-atom method (MEAM) interatomic potentials for the Ga-N and In-N binary and Ga-In-N ternary systems have been developed based on the previously developed potentials for Ga, In and N. The potentials can describe various physical properties (structural, elastic and defect properties) of both zinc-blende and wurtzite-type GaN and InN as well as those of constituent elements, in good agreement with experimental data or high-level calculations. The potential can also describe the structural behavior of Ga(1-x)In(x)N ternary nitrides reasonably well. The applicability of the potentials to atomistic investigations of atomic/nanoscale structural evolution in Ga(1-x)In(x)N multi-component nitrides during the deposition of constituent element atoms is discussed.

Atomic structure of misfit dislocations at InAs/GaAs(110)

Heteroepitaxy of InAs on GaAs(110) leads to the formation of subsurface misfit dislocations to relieve strain. These dislocations have been observed both with transmission electron microscopy (TEM) and scanning tunnelling microscopy (STM), and show regular spacing. Electronic structure calculations of the structure of the core of the dislocations, as well as their location within the epitaxial layer, are presented. The most stable location is found to be at the interface, with the core centred over In. Calculated strain profiles and the thickness at which dislocations should form are in good agreement with available experimental data.