Stopped depletion region extension in an AlGaN/GaN-HEMT: A new technique for improving high-frequency performance

Abstract

We present a novel structure for AlGaN/GaN high electron mobility transistors. The structure consists of a multi-recess AlGaN barrier layer and recessed metal ring (RBRM-HEMT). The barrier thickness narrowing between the gate and the source/drain regions minimizes the depletion region extension, which leads to smaller gate-drain (C GD ) and gate-source (C GS ) capacitances. This technique shows a great improvement in high-frequency and high-power applications. In high-frequency operation, the cut-off frequency (f T ) and the maximum oscillation frequency (f max ) of the RBRM-HEMT are found to be 133 GHz and 216 GHz respectively, which is significantly higher than the 94 GHz and the 175 GHz obtained for the conventional GaN HEMT (C-HEMT). In addition, a more uniform and low-crowding electric field is obtained under the gate close to the drain side due to the recessed metal-ring structure. A 128% improvement in breakdown voltage (V BR ) is achieved compared to the C-HEMT. Consequently, the maximum output power density (P max ) is increased from 11.3 W/mm in the C-HEMT to 24.4 W/mm for the RBRM-HEMT.