Formation, etching and electrical characterization of a thermally grown gallium oxide on the Ga-face of a bulk GaN substrate

Thermal oxides on the Ga-face of low defect density bulk gallium nitride (GaN) were controllably produced under varying conditions and subsequently analyzed. The thermal oxidation was performed in a dry oxygen atmosphere at different temperatures and different oxidation times. Each oxide layer was identified as the monoclinic β-Ga2O3 by a θ–2θ X-ray diffraction (XRD) scan. Complementary Auger electron spectroscopy (AES) and high-resolution X-ray photoelectron spectroscopy (XPS) were also performed to study the chemical and electronic states of the oxide. The surfaces of the as-grown oxide and the GaN surfaces (after oxide removal) were studied using scanning electron microscopy (SEM). The roughness of both surfaces was found to increase with increasing oxidation temperature. Schottky diodes were fabricated on the GaN surfaces after oxide removal to further examine the surface quality. An excess reverse leakage current was found for Schottky diodes fabricated on GaN surfaces that were oxidized at 950 °C or 1000 °C, indicating possible surface decomposition at these two temperatures. The characteristics of wet and dry etching of the gallium oxide layer were also investigated. Finally, metal–oxide–semiconductor (MOS) capacitors were fabricated using thermally oxidized bulk GaN substrates. Current–voltage (I–V) measurements showed a low reverse current of 1.5 pA at −10 V. The oxide breakdown field was determined to be 0.65 MV/cm. Capacitance–voltage (C–V) measurements displayed a deep depletion feature, and the interface trap density near the conduction band was estimated to be in the low 1011 eV−1 cm−2 range.