31 GHz power characteristics of GaN HEMTs with slightly etched AlGaN layer at ohmic contact

Slight etching of an AlGaN layer at ohmic contact was investigated to reduce contact resistance in AlGaN/GaN HEMTs in Ka-band operation. In the etching process, etched depth was precisely controlled by ICP-RIE system with a mixture of BCl3 and Cl-2 gases. The relation between ohmic contact resistance and etched depth was examined to determine the optimum depth. It was found that a resistance at an etched depth of 5 nm was reduced to 44% of that in the case of the conventional process. This process was applied to fabrication of GaN HEMTs with a gate length of 0.2 mu m, and Ka-band power characteristics were measured. The linear gain of the device was 11.4 dB, the maximum power-added efficiency was 45%, and the output power density was 5.1 W/mm, under the conditions of a frequency of 31 GHz, a drain bias of 24 V, and a class-AB operation. The values are higher than those in the case of the conventional process by 0.5 dB for the linear gain, 2 points for the power-added efficiency, and 11 % for the output power. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim