Simulation of GaN/AlGaN heterojunction bipolar transistors: part I – npn structures

Abstract

A drift-diffusion model was employed to calculate the dc performance of GaN/AlGaN heterojunction bipolar transistors (HBTs). The dc current gain was found to vary from ∼7 to 60 for collector currents of 10 −12–10 −2 A in 100 μm contact diameter devices with 2000 Å thick p-GaN base layers (P=2×10 17 cm −3) . The effects of base grading, base thickness, minority carrier lifetime and mobility in the base, base contact resistance and device operating temperature (25–300°C) were examined. The HBTs were found to have a significantly better gain at low collector current densities than the GaN bipolar junction transistors, due to the valence band offset.