Tunnel Junction-Enabled AlGaN/GaN Heterojunction Bipolar Transistors With All n-Type Contacts

The performance of contemporary GaN heterojunction bipolar transistors (HBTs) is currently limited by challenges associated with the formation of p-type contacts for the base terminal. In this article, we report on the design and demonstration of GaN HBTs with all n-type contacts for the emitter, base, and collector terminals. We show that degenerately doped GaN tunnel junctions (TJs) can be utilized to function as a base contact at reverse bias and as an emitter terminal at forward bias. We demonstrate device operation using a p ⁺ /n ⁺ GaN TJ sandwiched between a graded AlGaN emitter and a p-GaN base layer with an interdigitated emitter/base stripe design. The device displayed a high collector current density ( ${I} _{C}$ ) of 28 kA/cm ² extracted from the common emitter output ( ${I} _{\text {C}}$ – ${V} _{\text {CE}}$ ) characteristics. This novel approach to HBT design significantly advances the current field of III-nitride HBTs for the next-generation radio frequency (RF) and mm-Wave applications by circumventing the need to fabricate p-type contacts on the base as well as eliminating regrowth of the emitter/base epilayers.