Microwave performance of recessed gate Al_0.2Ga_0.8N/GaN HFETs fabricated using a photoelectrochemical etching technique

This is the first report on the fabrication of AlGaN/GaN HFETs which has a recessed gate structure achieved by the photoelectrochemical etching technique. Optimal photoelectrochemical wet etching conditions were stabilized and applied for the device fabrication. The DC and large-signal RF performance of thus fabricated device is presented as well. The ohmic contacts fabricated on the n⁺-GaN layer exhibited contact resistivity of mid 10^-6 Ω cm² and resulted in a linear I - V characteristics during an operation of device. The maximum drain-source current density is approximately 174 mA mm^-1 (at V_GS = 1 V), and the transconductance of approximately 68 mS mm^-1 (at V_GS = -1.1 V, V_DS = 6 V). The maximum frequency is measured to be approximately 31 GHz, and an RF power of 84 mW mm^-1 at 1.8 GHz for a 1400-μm wide gate device.