Growth and Characterization of Ultra-Wide-Bandgap MgGa2O4 Single Crystals

Abstract

High-temperature stable deep-ultraviolet (DUV) ultra-wide bandgap semiconductors hold significant application potential in the fields of light-emitting, power devices and solar-blind detection. In this work, high-temperature thermally stable MgGa2O4 single crystals were grown and systematically studied. Large-size bulk MgGa2O4 single crystals were successfully prepared by vertical gradient freeze (VGF) method and their structural, optical, electrical, thermal properties were systematically evaluated. Powder X-ray diffraction (XRD) and Laue diffraction confirmed a cubic crystal structure. Ultraviolet spectroscopy revealed a cutoff at 250 nm for the (111) plane, corresponding to an optical bandgap of ~4.96 eV. The luminescence properties and elemental bonding environments of MgGa2O4 were investigated by photoluminescence (PL) spectroscopy and X-ray photoelectron spectroscopy (XPS). Unintentionally doped MgGa2O4 crystals exhibit a high-resistivity state over a wide temperature range, retaining a high resistivity of 3.15 × 108 Ω·cm even at 800°C. The high infrared transmittance of approximately 80% further confirms the low carrier concentration. The defect energy level determined by fitting with the Arrhenius equation is approximately 1.28 eV near the relevant band edge. At room temperature, the thermal diffusion coefficient is 5.067 mm²/s, and the thermal conductivity is 13.067W/(m·K). Both parameters showed an anomalous increase around 900°C, which is attributed to ionic thermal transport from the hopping of Mg2+ and Ga3+ between lattice sites. Furthermore, MgGa2O4 demonstrates superior thermal stability in a gas mixture of 5 % H₂ and 95 % Ar annealing compared to β-Ga2O3. Benefiting from its high symmetry, large bandgap, and excellent high-temperature stability, MgGa2O4 shows high promise for high-temperature detectors, power devices, and as a substrate material for nitrides.