Preparation of controllable double-selective etched porous substrate for HVPE growth of GaN crystals with excellent optical properties

Abstract

Heteroepitaxial growth of GaN will inevitably generate a large number of defects; serious residual stress will be caused by the mismatch of the lattice and thermal expansion coefficient between the substrate and the GaN material, and eventually the crystal may be broken. We designed a double selective etching method, which can flexibly control the etching rate and degree of GaN substrates. And a hydrothermal etching buffer substrate (hydrothermal MOCVD GaN/Al₂O₃, HMGA) composed of a porous buffer layer with a weak connection between seed layer and a sapphire substrate was obtained. The 4-inch GaN crystal with excellent optical properties and a thickness of approximately 3 mm was successfully grown on the HMGA substrate. The crystal quality and optical quality of the as-obtained GaN crystal were greatly improved and the residual stress was reduced. At the same time, a metal–semiconductor–metal (MSM) structure ultraviolet (UV) photodetector was made using the as-obtained GaN crystal which showed good photoresponse in the UV band. These prove that the double selective etching technology has broad application prospects in heteroepitaxial growth of semiconductor materials.