Fin- and Island-Isolated AlGaN/GaN HFETs

The effects of the variation of the size of isolation mesa of AlGaN/GaN heterojunction field-effect transistors (HFETs) on the device characteristics are presented for the first time. Studies on the direct current and pulsed drain and gate current-voltage characteristics demonstrate a correlation between the pinchoff voltage and the size of the isolation mesa. In this paper, devices fabricated on narrow mesas (i.e., 16 × 40 μm² fins) and also a device fabricated on an array of very small size mesas (i.e., 16 × 7 μm² islands) are compared with AlGaN/GaN HFETs of traditionally sized mesas (i.e., 70 × 100 μm²). All these devices show maximum extrinsic gate transconductance greater than 220 mS/mm, whereas the pinchoff voltage is observed to become less negative by reducing the size of the individual mesas. The island-isolated HFETs also enjoy a relatively higher gate transconductance.