Selective injection AlGaN/GaN heterojunction bipolar transistors with patterned regrown base contacts

Abstract

We demonstrate graded AlGaN/GaN heterojunction bipolar transistors (HBTs) with selective injection of minority carriers across a p-GaN base and patterned regrown base contacts. The selective injection design regulates minority carrier transport under emitter-base forward bias through a thin base region, while thick and highly doped p${}^{+}$ GaN regrown layers patterned alongside the thin base regions are utilized to lower the base contact resistance. With SiO${}_2$ employed as a spacer between the emitter and the p${}^{+}$ regrown layers, the device with an interdigitated emitter/base-contact stripe design displayed a maximum collector current density (I${}_C$) of 101 kA/cm${}^2$, a maximum current gain ($\beta$) of 70 at I${}_C$ $\sim$ 1 kA/cm${}^2$ and $\sim$ 11 for I${}_C$ $>$ 50 kA/cm${}^2$. The reported results demonstrate the potential of the selective injection approach to break the long-existing HBT design tradeoff between base resistance and current gain for next-generation radio frequency and mm-Wave applications.