Surface passivation of aln/gan mos-hemts using ultra-thin al2o3 formed by thermal oxidation of evaporated aluminium

A simple method is reported for fabrication of AlN/GaN MOS-HEMTs. Ultra-thin Al₂O₃, which is formed using thermal oxidation of evaporated Al, was used for surface passivation and as a gate dielectric. Prior to formation of Al₂O₃, the Al protects the very sensitive AlN epilayer from exposure to processing liquid chemicals. Fabricated two-finger AlN/GaN MOS-HEMTs with 3 m gate length and 200 m gate width showed good gate control of drain currents up to a gate bias of 3 V and achieved a maximum drain current, I_DSmax, of ~900~mA/mm. The peak extrinsic transconductance, G_max, of the device is ~100~mS/mm at V_DS = 8=V. Capacitance-voltage (C-V) characteristics of Al₂O₃/AlN/GaN circular test MOS structures were observed and measured. They exhibited no hysteresis, indicating the good quality of the thermally grown Al₂O₃ for realising AlN/GaN MOS-HEMTs for high power and high frequency applications.