N-AlGaN/p-InGaN/n-GaN heterojunction bipolar transistors for high power operation

We have fabricated N-AlGaN/p-InGaN/n-GaN heterojunction bipolar transistors to evaluate their common-emitter current-voltage (I-V) characteristics at room temperature. The device has a Si-doped N-AlGaN emitter, a Mg-doped p-InGaN base, and a Si-doped n-GaN collector. The common-emitter I-V characteristics were observed up to a collector-emitter voltage of 70 V and a collector current of 14.5 mA. The breakdown voltage is as high as 100 V. The corresponding breakdown electric field is 2 × 10⁶ V/cm, which is comparable to the expected one for GaN. This high breakdown electric field is ascribed to a less damaged p-InGaN and a wide bandgap of an n-GaN collector. Furthermore, the leakage path through the defects in InGaN layers is considered to be eliminated by filling them with wide bandgap AlGaN layers during the emitter growth.