Effect of Oxygen and Aluminum Incorporation on the Local Structure of GaN Nanowires: Insight from Extended X-ray Absorption Fine Structure Analysis

Abstract

A thorough investigation of local structure, influencing macroscopic properties of the solid is of potential interest.We investigated the local structure of GaN nanowires (NWs) with different native defect concentration synthesized by the chemical vapor deposition technique. Extended X-ray absorption fine structure (EXAFS) analysis and semi-empirical and the density functional theory (DFT) calculations were used to address the effect of dopant incorporation along with other defects on the co-ordination number and bond length values. The decrease of the bond length values along preferential crystal axes in the local tetrahedral structure of GaN emphasizes the preferred lattice site for oxygen doping. The preferential bond length contraction is corroborated by the simulations. We have also studied the impact on the local atomic configuration of GaN NWs with Al incorporation. AlxGa1-xN NWs are synthesized via novel ion beam techniques of ion beam mixing and post-irradiation diffusion process. The 2 change in the local tetrahedral structure of GaN with Al incorporation is investigated by EXAFS analysis. The analysis provides a clear understanding of choosing a suitable process for ternary III-nitride random alloy formation. The local structure study with the EXAFS analysis is corroborated with the observed macroscopic properties studied using Raman spectroscopy.

Optical, Structural, and Synchrotron X-ray Absorption Studies for GaN Thin Films Grown on Si by Molecular Beam Epitaxy

“…Synchrotron radiation (SR) X-ray absorption fine structure (XAFS) technology has been applied to the study of GaN materials [ 41 , 42 , 43 , 44 ]. Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy measures the variation of the absorption coefficient versus the incident X-ray photon energy near the absorption edge.…”

“…Figure 11 a shows the Ga K-edge XAFS spectra of four GaN/Si samples. Two spectral regions are marked: X-ray absorption near edge structure (XANES) near Ga K-edge within about 30 keV, from which information about the local symmetry and various electronic transitions can be obtained [ 44 ], and the extended X-ray absorption near edge structure (EXANES), from which information about radial distance and coordination number of the absorbing atom can be deduced [ 44 ]. Figure 11 b presents their Fourier transformation from k to R space of Ga K-edge EXANES.…”

“…Figure 12 b shows the spectral data converted from the energy scale to the k -space scale with a k 2 -weigthed multiplication. Subsequently, following Figure 12 a,b, the Fourier transform of raw data and fitting were done by using the IFEFFIT program [ 41 , 44 ], with results shown in Figure 12 c–e. The chi data, i.e., k 2 χ (k) weighed spectra in Figure 12 b, were Fourier transformed to the R-space data.…”

“…It probes the conduction band of crystalline materials, electron dipole transitions, the bonding state, and orientation of 3.6. Near-Edge X-ray Absorption Fine Structure (NEXAFS) of GaN on Si Synchrotron radiation (SR) X-ray absorption fine structure (XAFS) technology has been applied to the study of GaN materials [41][42][43][44]. Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy measures the variation of the absorption coefficient versus the incident X-ray photon energy near the absorption edge.…”