The effect of ohmic contact location on the buffer leakage current of AlGaN/GaN heterostructure was investigated and the AlGaN/GaN HEMT employing the proposed ohmic contact pattern was fabricated. We have fabricated 3 different types of ohmic patterns; type A - both contacts are on the etched GaN buffer layer, type B - one is on the etched GaN buffer layer and the other is on the unetched GaN cap layer and type C - both contacts are on the unetched GaN cap layer. Our experimental results showed that the ohmic contact on GaN buffer increased the buffer leakage current due to the lateral diffusion of ohmic metals. The proposed AlGaN/GaN HEMT successfully decreased the leakage current and did not affect the forward drain current and the transconductance.

AlGaN/GaN HEMTs employing a tapered field plate, which decreases the gate leakage current and improves the breakdown voltage without any sacrifice of the forward electrical characteristics were proposed and fabricated. The tapered structure was fabricated by the wet etching process. The depletion region of the proposed structure expands toward the slope of the tapered field plate and the electric field concentration at the gate edge can be successfully suppressed. The gate leakage current of proposed device at VGS= -5 V and VDS= 100 V was decreased by 2-3 orders compared with that of the conventional one. The breakdown voltage of proposed device was 880 V while that of conventional one was 548 V.

We have fabricated SiO2 passivated AlGaN/GaN HEMTs and employed As+ ion implantation on the passivation layer and optimized the implantation energy. After As+ ion implantation with 120 keV energy and 1 × 1014 /cm2 dose, the maximum drain current, maximum transconductance and the breakdown voltage increased to 419.6 mA/mm, 87.9 mS/mm and 698 V while those of the conventional device was 317.0 mA/mm, 65.1 mS/mm and 639 V, respectively.