Semipolar (112¯2) GaN Films Improved by in situ SiN_x Pretreatment of m‐Sapphire Substrate Surface

Abstract

The authors report on growth and characterization of semipolar (11 22) GaN films improved by an in situ SiN x pretreatment of m-sapphire substrate surface. Formation of SiN x and Ga-rich surface at the initial growth stages is evidenced by X-ray photoelectron spectroscopy. With the SiN x pretreatment, the GaN nucleated island density decreases due to the reduction of nucleation density by the SiN x mask. X-ray diffraction and Raman analyses show reduction of threading defect density for the SiN x pretreated GaN films. Cathodoluminescence studies show enhanced D 0 X emission and suppressed defect-related emissions. The improvements in crystalline quality and optical properties of semipolar GaN films with the SiN x pretreatment are attributed to the reduction in nucleated island density and coalescence boundaries, and enhancement of the þc island sidewall facet growth under Ga-rich growth conditions.