Local electronic structure of Cu-doped GaN investigated by XANES and x-ray linear dichrosim

Abstract

X-ray absorption near edge structure (XANES) and x-ray linear dichroism (XLD) measurements of a series of Cu-doped GaN samples with different doping concentrations were investigated at the Ga and Cu $K$ edges to get insight into the preferred occupation site of Cu in the GaN matrix. The XLD data of the Cu $K$ edge clearly demonstrates that Cu is incorporated in the GaN film. $\ensuremath{\gamma}$-Cu${}_{9}$Ga${}_{4}$ compounds that formed on the samples during the GaN growth process could be partially removed by etching with HNO${}_{3}$. At both absorption edges, a clear increase of the XLD signal intensity could be observed after etching as a consequence of the removal of the $\ensuremath{\gamma}$-Cu${}_{9}$Ga${}_{4}$ compounds. By performing simulations of XANES and XLD spectra, which are compared to the experimental data, it was possible to show that most Cu in the GaN film is incorporated on Ga or interstitial sites and only a minor fraction on N sites.