Local structure of (Ga,Fe)N and (Ga,Fe)N:Si investigated by x-ray absorption fine structure spectroscopy

TL;DR

This study uses X-ray absorption spectroscopy and DFT calculations to analyze the local structure and electronic states of Fe-doped GaN and Si co-doped GaN, revealing how growth conditions influence Fe site occupancy, precipitation, and charge state.

Contribution

It provides a detailed characterization of Fe and Si doping effects in GaN using combined experimental and computational methods, highlighting the conditions that prevent Fe precipitation and alter its charge state.

Findings

Fe atoms occupy Ga sites or form Fe3N nanocrystals depending on growth conditions.

Si co-doping reduces Fe from Fe3+ to Fe2+ and suppresses Fe precipitation.

Growth parameters influence Fe site occupancy and magnetic properties.

Abstract

X-ray absorption fine-structure (XAFS) measurements supported by {\em ab initio} computations within the density functional theory (DFT) are employed to systematically characterize Fe-doped as well as Fe and Si-co-doped films grown by metalorganic vapour phase epitaxy. The analysis of extended-XAFS data shows that depending on the growth conditions, Fe atoms either occupy Ga substitutional sites in GaN or precipitate in the form of $\epsilon$-Fe$_3$N nanocrystals, which are ferromagnetic and metallic according to the DFT results. Precipitation can be hampered by reducing the Fe content, or by increasing the growth rate or by co-doping with Si. The near-edge region of the XAFS spectra provides information on the Fe charge state and shows its partial reduction from Fe$^{+3}$ to Fe$^{+2}$ upon Si co-doping, in agreement with the Fe electronic configurations expected within various implementations of DFT.