Electronic structure of GaN and Ga investigated by soft x-ray spectroscopy and first-principles methods

Abstract

The electronic structure and chemical bonding of wurtzite-GaN investigated by $\text{N}\text{ }1s$ soft x-ray absorption spectroscopy and $\text{N}\text{ }K$, $\text{Ga}\text{ }{M}_{1}$, and $\text{Ga}\text{ }{M}_{2,3}$ emission spectroscopy is compared to that of pure Ga. The measurements are interpreted by calculated spectra using first-principles density-functional theory (DFT) including dipole transition matrix elements and additional on-site Coulomb interaction $(\text{WC-GGA}+U)$. The $\text{Ga}\text{ }4p\text{-N}\text{ }2p$ and $\text{Ga}\text{ }4s\text{-N}\text{ }2p$ hybridization and chemical bond regions are identified at the top of the valence band between $\ensuremath{-}1.0$ and $\ensuremath{-}2.0$ and further down between $\ensuremath{-}5.5$ and $\ensuremath{-}6.5\text{ }\text{eV}$, respectively. In addition, $\text{N}\text{ }2s\text{-N}\text{ }2p\text{-Ga}\text{ }4s$ and $\text{N}\text{ }2s\text{-N}\text{ }2p\text{-Ga}\text{ }3d$ hybridization regions occur at the bottom of the valence band between $\ensuremath{-}13$ and $\ensuremath{-}15\text{ }\text{eV}$, and between $\ensuremath{-}17.0$ and $\ensuremath{-}18.0\text{ }\text{eV}$, respectively. A bandlike satellite feature is also found around $\ensuremath{-}10\text{ }\text{eV}$ in the $\text{Ga}\text{ }{M}_{1}$ and $\text{Ga}\text{ }{M}_{2,3}$ emission from GaN, but is absent in pure Ga and the calculated ground-state spectra. The difference between the identified spectroscopic features of GaN and Ga are discussed in relation to the various hybridization regions calculated within band-structure methods.