Influence of polycrystalline diamond on silicon-based GaN material

Abstract

Self-heating effect has been the limited factors for the performance improvement of GaN electronics. Directly growth of polycrystalline diamond on GaN material to solve the heating problem of GaN devices becomes one of the resraech highlights. Polycrystalline diamond on Si-based GaN material has the advantages of being close to the channel region and having high heat dissipation efficiency. But there is a problem that the thermal expansion mismatch between polycrystalline diamond and GaN material leads to the electrical characteristics deterioration of GaN. In this work, we adopted microwave plasma chemical vapor deposition (MPCVD) method to grow polycrystalline diamond on 2-inch Si-based GaN material. The test results showed that polycrystalline diamond was uniform as a whole. The average thicknesses are 9~81 μm. With the thickness increase of polycrystalline diamond, the XRD (002) diffraction peak FWHM increment and mobility loss gradually increased for the Si-based GaN material. Through laser cutting and acid etching, the Si-based GaN material was successfully peeled off from the polycrystalline diamond. It was found that during the high temperature growth of diamond, hydrogen atoms had an etching effect on the defect positions of the silicon nitride epitaxial layer to form a hole region in the GaN, and the etching depth can reach the intrinsic GaN layer. During the cooling process, a crack region formed around the hole region. The Raman characteristic peaks, XRD (002) diffraction peaks FWHM, and electrical properties of the exfoliated Si-based GaN materials all returned to their intrinsic states. The above results indicated that the thermal expansion mismatch between polycrystalline diamond and Si-based GaN introduced stress to GaN, which caused the GaN lattice distortion, and leading to electrical property degradation of GaN material. The degradation of GaN material was recoverable rather than destructive.