Contact engineering of GaN-on-silicon power devices for breakdown voltage enhancement

Two contact engineering approaches are proposed and investigated to enhance the breakdown voltage VBK in GaN-on-Si power devices, including the hybrid Schottky–ohmic-drain structure for AlGaN/GaN HEMTs and the selective Si-diffusion structure for AlGaN/GaN SBDs. With the hybrid Schottky–ohmic drain, the devices showed a zero onset voltage and reduced off-state leakage current by one order of magnitude, compared with that of the traditional ohmic-drain devices. The breakdown voltage was also enhanced with comparable on-resistance. For the SBDs with the selective silicon-diffusion layer underneath ohmic metal at the cathode, a low-contact resistance Rc of 0.2 Ω mm and a smooth ohmic metal morphology were obtained. The SBDs with the additional silicon diffusion layer showed enhanced VBK, compared with that of the conventional SBDs. The results demonstrate that the proposed contact engineering approaches are useful for the breakdown voltage enhancement of GaN-on-Si power devices. (invited paper)