Effect of Buffer Oxide Etchant (BOE) on Ti/Al/Ni/Au Ohmic Contacts for AlGaN/GaN Based HEMT

The effects of buffer oxide etchant on Ti/Al/Ni/Au Ohmic contacts for AlGaN/GaN high electron mobility transistor were studied. Scanning electron microscopy (SEM), energy dispersive spectrum (EDX), and Auger electron spectroscopy (AES) were performed to investigate the degradation after treatment. Contact resistance increase from 1×10-4 to 2.5×10-4 ohm/cm2 after treatment. Ohmic metals were found out to be divided into three regions including islands, rings surround the islands, and the remaining field area. The islands were found to be shorter and the rings thinner after treatment. Besides, Ti, Al and Ni were found to be etched by BOE and caused Au to peel off from the Ohmic metals. The etching of Ti, Al and Ni was believed to be the reason of degradation.