Analysis of high DC current gain structures for GaN/InGaN/GaN HBTs

AlGaN/GaN HBTs with DC current gains in excess of 10 have been demonstrated; however, Makimoto et al. have recently obtained a DC current gain value exceeding 2000 for a GaN/InGaN/GaN triple mesa DHBT. The experimental demonstration of a GaN-based HBT with such extraordinary DC current gain has motivated the search for new device structures conducive to high DC current gain. Simulations in this work indicate that high DC current gain is difficult to achieve with a uniform, defect-free base layer. We also simulate the electrical characteristics of a new class of DHBT where the base layer is non-uniform. By non-uniformly thinning or perforating the base, the majority of the base would remain thick to minimize the negative impact to base resistance. However, small thinned regions achieve extremely high DC current gain, which can be used to significantly increase the overall DC current gain. This device structure could naturally occur when "V" defects form or indium is non-uniformly distributed during the base layer growth. The sensitivity of DC current gain to the base thickness range, duty cycle, defect geometry, and defect type is also investigated.