GaN/InGaN heterojunction bipolar transistors with ultra‐high d.c. power density (>3 MW/cm 2 )

We report ultra‐high‐power performance on npn GaN/InGaN double heterojunction bipolar transistors (DHBTs) that is directly grown on a free‐standing (FS) GaN substrate. Measured common‐emitter current gain ( h fe ) reaches 80. A quasi‐static I – V measurement shows that J C  > 141 kA/cm 2 and a power density of 3.05 MW/cm 2 can be achieved for DHBTs grown on an FS‐GaN substrate. When the temperature is increased to 250 °C, a GaN/InGaN DHBT shows h fe  = 43 and the offset voltage is reduced from 0.8 V at the room temperature to 0.3 V. Similarly, the knee voltage is reduced from 5.2 V at room temperature to 2.75 V at 250 °C. In this particular device, breakdown voltage (BV CEO ) increases from 90 V at room temperature to 157 V at 250 °C.