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

A drift-diffusion model was employed to calculate the de performance of GaN /AlGaN heterojunction bipolar transistors (HBTs). The dc current gain was f ound to vary from similar to 7 to 60 for collector currents of 10(-12)-10(- 2) A in 100 mu m contact diameter devices with 2000 Angstrom thick p-GaN ba se layers (P = 2 x 10(17) cm(-3)). The effects of base grading, base thickn ess, minority carrier lifetime and mobility in the base, base contact resis tance and device operating temperature (25-300 degrees C) were examined. Th e HBTs were found to have a significantly better gain at low collector curr ent densities than the GaN bipolar junction transistors, due to the valence band offset. (C) 2000 Elsevier Science Ltd. All rights reserved.