Processing and characterization of a free-standing bulk polycrystalline GaN layer

Abstract

This work reports a new processing of producing a free-standing bulk polycrystalline GaN layer. Specifically, a ∼0.05 mm thick GaN layer was deposited onto a Si substrate by e-beam evaporator and subsequently was being subjected to ammonia annealing in order to improve its material quality. The Si substrate was then separated from the GaN layer through a chemical wet etching, hence resulted a free-standing bulk polycrystalline GaN layer. It was found that the surface of the free-standing bulk polycrystalline GaN layer that was previously in contact with the Si substrate has a better surface than the top side of the layer, despite of the presence of voids on the surface. The free-standing bulk polycrystalline GaN layer exhibited XRD peaks related to GaN material, mainly at (101¯0), (0002) and (101¯1) orientations without any significant evidence from other materials like Ga2O3. The peak of E2 (high) and A1 (LO) phone modes of the free-standing bulk polycrystalline GaN layer were clearly observed in a Raman spectrum. From the E2 (high) peak, the in-plane biaxial stress of the layer was estimated to be 0.93 GPa, suggesting that the free-standing bulk polycrystalline GaN layer was under tensile stress. Nonetheless, no cracks were observed on the surface and this is due to the presence of the voids that partially reduced the micro-strains inside the layer.