GaN/SiC heterojunction bipolar transistors

We report on the evolution of the fabrication and characterization of high- temperature and high-power GaN/SiC n-p-n heterojunction bipolar transistors (HBTs). The HBT structures consists of an n-type GaN emitter and a SiC p-n base/collector. Initially, the HBTs were fabricated using reactive ion etc hing (RIE) to define both the emitter and base areas. However, the poor etc h selectivity between GaN and SiC made it difficult to stop at the thin bas e layer. Furthermore, the RIE caused damage at the heterojunctions, which r esulted in large leakage currents. Selective area growth was therefore empl oyed to form the n-GaN emitters. GaN/SiC HBTs were first demonstrated using the 6H-polytype. These transistors had an extraordinary high de current ga in of >10(6) at room temperature and were able to operate at 520 degrees C with a current gain of 100. However, in more recent work, this performance could not easily be reproduced due to the presence of a parasitic deep defe ct level in the p-type 6H-SiC. The possibility of obtaining higher quality 4H-SiC than 6H-SiC, without this defect level, seemed promising since much of the materials development is focused on 4H-SiC, due to its larger energy band gap and superior electron mobility. GaN/4H-SiC HBTs are demonstrated with a modest de current gain of 15 at room temperature and 3 at 300 degree s C. (C) 2000 Elsevier Science Ltd. All rights reserved.