Extrinsic Base Regrowth of p-InGaN for Npn-Type GaN/InGaN Heterojunction Bipolar Transistors

The regrowth of p-InGaN as the extrinsic base layer of Npn-type GaN/InGaN heterojunction bipolar transistors (HBTs) significantly improves the ohmic characteristics of the base layer. The specific contact resistance is 7.8×10-4 Ω·cm2 even after the dry etching. This value for a non-alloyed ohmic contact is much better than that for as-grown p-GaN (1.7×10-3 Ω·cm2) and decreased turn-on voltage in the emitter-base diodes, which results in high current gains of up to 2000 and reduced offset voltages in the GaN/InGaN HBTs. These results show that the p-InGaN extrinsic base regrowth is an effective way to improve nitride HBT characteristics.