Selective-injection GaN Heterojunction Bipolar Transistors with 275 kA/cm$^2$ Current Density

TL;DR

This paper introduces a novel selective injection GaN heterojunction bipolar transistor design that achieves a record current density of 275 kA/cm$^2$, promising advancements in RF and mm-Wave technologies.

Contribution

The paper presents a new selective injection design for GaN HBTs utilizing patterned bases and regrowth emitter techniques, significantly improving current density and device performance.

Findings

Achieved a maximum output current density of 275 kA/cm$^2$

Demonstrated a current gain ($eta$) of 9 in the novel design

Compared performance with planar HBT, showing superior current density

Abstract

We design and demonstrate selective injection GaN heterojunction bipolar transistors that utilize a patterned base for selective injection of electrons from the emitter. The design maneuvers minority carrier injection through a thin p-GaN base region, while the majority carrier holes for base current are injected from thick p-GaN regions adjacent to the thin p-GaN base. The design is realized using a regrowth emitter approach with SiO$_2$ as a spacer between the emitter layer and the thick p-GaN base contact regions. The fabricated device demonstrated state-of-art output current density (I$_{C, max}$) ~275 kA/cm$^2$ with a current gain ($\beta$) of 9, and 17 for the planar HBT design (I$_{C, max}$ =150 kA/cm$^2$). The reported results highlight the potential of the selective injection design to overcome the persistent GaN HBT design tradeoff between base resistance and current gain, paving the way for next-generation radio frequency and mm-Wave applications.