Ir4+ ions in β-Ga2O3 crystals: An unintentional deep donor

Electron paramagnetic resonance (EPR) and infrared absorption are used to detect Ir4+ ions in beta-Ga2O3 crystals. Mg and Fe doped crystals are investigated, and concentrations of Ir4+ ions greater than 1 x 10(18) cm(-3) are observed. The source of the unintentional deep iridium donors is the crucible used to grow the crystal. In the Mg-doped crystals, the Ir4+ ions provide compensation for the singly ionized Mg acceptors and thus contribute to the difficulties in producing p-type behavior. The Ir4+ ions replace Ga3+ ions at the Ga(2) sites, with the six oxygen neighbors forming a distorted octahedron. A large spin-orbit coupling causes these Ir4+ ions to have a low-spin (5d(5), S = 1/2) ground state. The EPR spectrum consists of one broad line with a significant angular dependence. Principal values of the g matrix are 2.662, 1.815, and 0.541 (with principal axes near the crystal a, b, and c directions, respectively). Ionizing radiation at 77 K decreases the Ir4+ EPR signal in Mg-doped crystals and increases the signal in Fe-doped crystals. In addition to the EPR spectrum, the Ir4+ ions have an infrared absorption band representing a d-d transition within the t(2g) orbitals. At room temperature, this band peaks near 5153 cm(-1) (1.94 mu m) and has a width of 17 cm(-1). The band is highly polarized: its intensity is maximum when the electric field E is parallel to the b direction in the crystal and is nearly zero when E is along the c direction. Published under license by AIP Publishing.