Electronic structure and properties of trapped holes in crystalline and amorphous Ga2O3

Structure and electronic properties of self-trapped holes were studied in both crystalline and amorphous Ga2O3 using density functional theory (DFT) and the nonlocal PBE0-TC-LRC density functional. Amorphous (a) Ga2O3 structures were generated using classical molecular dynamics and the melt-quench technique and further optimized using DFT. They exhibit an average density of 4.84 g/cm3 and band gap around 4.3 eV. Calculations predict deep hole trapping in crystalline and amorphous phases with the hole-trapping energies in the amorphous structures being deeper than those found in the crystalline structure. In a-Ga2O3, trapped holes are localized around low-coordinated oxygen atoms (two or three coordinated). We predict the formation of stable hole bipolarons in both the crystalline and amorphous phases facilitated by the formation of O-O bonds with binding energies about 0.2 eV.