A three-step surface treatment and its impacts on electrical properties of c- and m-face GaN/Al2O3 MOS structures

Abstract

In this study, a three-step surface treatment, composed of SiO₂ deposition, subsequent annealing, and SiO₂ removal, is adopted for the fabrication of c- and m-plane n-type GaN/Al₂O₃ MOS structures, and the impact of the proposed process on electrical properties and its crystal face dependence are systematically investigated. While no significant changes are observed after the proposed surface treatment for m-face GaN, an identical process causes changes in the properties of c-face GaN MOS structures: an about 0.2 V lower flat-band voltage (V_FB) and an about 0.2 eV higher conduction band offset, associated with a change in the thickness or crystalline quality of a gallium oxide (GaO${}_x$) layer on the c-face GaN surface. The modified energy band alignment leads to a reduced gate leakage current, reducing the V_FB drift after high-field positive bias stress (4.5 MV/cm) almost by half only for c-face GaN MOS structures. The fact that even an identical process has a crystal face-dependent impact on the properties of GaN MOS structures is important in developing the fabrication process of GaN planar and trench MOSFETs.