High Off-state Breakdown Voltage 60-nm-Long-Gate AlGaN/GaN Heterostructure Field-Effect Transistors with AlGaN Back-Barrier

We fabricated 60-nm-long-gate AlGaN/GaN heterostructure field-effect transistors (HFETs) with an AlGaN back-barrier structure and investigated the high frequency device characteristics and three-terminal off-state breakdown characteristics as a function of the source-to-drain distance. These devices, with source-to-drain distances of 2 to 5 µm, showed very high current-gain cutoff frequencies of more than 118 GHz. The off-state breakdown characteristics were largely dependent on the source-to-drain distance compared to the high frequency device characteristics, and the devices with source-to-drain distances of 4 and 5 µm exhibited very high off-state breakdown voltages of more than 110 V while keeping very high cutoff frequencies. These good breakdown characteristics might be the result of the double-barrier structure (i.e., AlGaN/GaN/AlGaN), which prevents electron spillover to the AlGaN back-barrier at high power conditions.