Design and optimization of area-selective carrier modulation in β-Ga₂O₃ through high temperature oxygen annealing

Carrier modulation in beta-gallium oxide (β-Ga₂O₃) films through an oxygen annealing method is systematically investigated, including annealing time and annealing cap layer (ACL) design. Capacitance–voltage measurement conducted on vertical SBD structures was used to evaluate the carrier concentration after annealing. The formation of a “surface layer” may suppress the diffusion of oxygen species as the annealing time increases. An 8-hour annealing time resulted in a carrier modulation with an approximately 3-μm-deep low-carrier-concentration layer. The annealing cap layer, consisting of poly-Si and SiO₂, was deposited and patterned to achieve area-selective carrier modulation in β-Ga₂O₃. The effective thickness of poly-Si for blocking oxygen diffusion was confirmed by scanning electron microscopy (SEM) for the first time. A definite thickness of SiO₂ served as both etching stop layer and lift-off layer for poly-Si. According to simulation results, the non-ideal surface caused extra high peak electric field in the β-Ga₂O₃ device. A combination of an optimized dry etching method and low-compressive-stress deposition technology was employed to eliminate the bird’s beak-like shape structure that appeared at the edges of the patterns and bulges on the β-Ga₂O₃ surface after annealing. The feasibility of the carrier modulation technology enables the diversity of β-Ga₂O₃ devices fabrication.