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

TL;DR

This paper presents a novel AlGaN/GaN heterojunction bipolar transistor design with selective carrier injection and patterned regrown base contacts, achieving high current density and gain, promising for advanced RF and mm-Wave devices.

Contribution

The work introduces a selective injection approach combined with patterned regrown base contacts to improve HBT performance, addressing longstanding tradeoffs in base resistance and current gain.

Findings

Maximum collector current density of 101 kA/cm²

Current gain of 70 at 1 kA/cm²

Enhanced device performance for RF applications

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.