Freestanding patterned polycrystalline GaN substrate by a straightforward and affordable technique

A new process for producing a freestanding patterned polycrystalline GaN substrate by applying a straightforward and affordable technique is presented here. Such substrate was fabricated by depositing ~ 50 µm thick bulk GaN layer on porous Si/Si substrate by e-beam evaporator with successive ammonia annealing to improve the material quality of the GaN layer. The GaN layer was then separated from the porous Si/Si substrate by immersing in an acidic solution. The surface of the freestanding patterned polycrystalline GaN substrate that was in contact with the porous Si/Si substrate consisted of cubic-like structures, as inherited from the porous Si/Si substrate. Although the cubic-like structures were almost uniformly distributed on the surface, they were formed in various heights due to irregular degree of symmetry of the porous Si/Si substrate. X-ray diffraction results suggested that β-Ga₂O₃ inclusions are inside the freestanding patterned polycrystalline GaN substrate but not on its surface. This was supported by micro-photoluminecsence (PL) measurement, whereby only the GaN PL signals were observed. Furthermore, Raman spectroscopy revealed a small amount of compressive stress (0.23 GPa), suggesting that the substrate was almost relaxed.