Local structural change in GaCrN grown by radio frequency plasma-assisted molecular-beam epitaxy

Local structural change around Cr atoms in GaN-based diluted magnetic semiconductor GaCrN grown by radio frequency plasma-assisted molecular-beam epitaxy was studied with fluorescent X-ray absorption fine structure (XAFS) and X-ray diffraction measurements. The lattice constant of Ga 1− x Cr x N depends linearly on x up to x = 4 % and it approaches to that of non-doped GaN above x of 4.7%. It was found from our XAFS study that the majority of Cr atoms substitute the Ga lattice sites of GaN and that the critical Cr concentration of solid solution is around x = 4 % . At the critical Cr concentration, onset of the formation of NaCl-type CrN-like structure occurs, and above the critical concentration, the local structure around Cr atoms transforms to a completely CrN-like structure. Our X-ray absorption near-edge structure studies also indicate a drastic change in local electronic structure of Ga 1 −x Cr x N at x between 4% and 4.7%. This is ascribed to the fact that the atomic configuration of Cr and N undergoes a drastic transition from the substitutionally incorporated GaCrN into the CrN-like atomic configuration. The local structural change into NaCl-type CrN was also supported by the XAFS pre-edge structures and the polarized XANES spectra.