Indium defect complexes in (In _x Ga_1−x )₂O₃: a combined experimental and hybrid density functional theory study

Abstract

Indium defects in small concentration (Inx<sub>Ga<sub>1-x<sub>)<sub>2<sub>O<sub>3<sub> were studied using a combination of spectroscopic and magnetic measurements on thin films varying the indium concentration, coupled with hybrid density functional theory simulations using the supercell method. X-ray diffraction spectra along with Tauc plots and density of states plots reveal a decrease (increase) in the electronic band gap (interlayer lattice spacing) due to the inclusion of indium in monoclinic Ga<sub>2<sub>O<sub>3<sub>, while room-temperature Hall measurements show an increase in n-type conductivity. Formation energy calculations reveal that the defect complex of substitutional indium at the octahedrally coordinated cation site (In<sub>Ga<sub>) coupled with an indium interstitial (In<sub>i<sub>) in the largest Ga-O cavity in the bulk (i<sub>a<sub>), where the two impurities are a maximal distance away in the unit cell, results in the lowest formation energy across much of the electronic band gap; near the conduction band edge the single In<sub>Ga<sub> defect becomes the lowest energy defect, though. These calculations help shed light on the impurity band enhanced, n-type conductivity increase due to small concentration indium doping in Ga<sub>2O<sub>3<sub> as seen in the spectroscopic/magnetic measurements.