Effects of the emitter conductivity on the electrical behaviour of an a-Si:H/c-Si HBT

Abstract

Heterojunction n-p-n bipolar transistors (HBTs) with a hydrogenated amorphous silicon (a-Si: H) emitter have recently emerged as very attractive devices but the electrical properties of the first structures studied were very poor in comparison with the prediction of modelling. The main limiting parameter appears to be the conductivity of the a-Si: H thin-film emitter. This paper focuses on the study of the effect of this conductivity on the electrical characteristics of the HBT in connection with the a-Si: H deposition conditions, distinguishing the cases of high and low conductivity. In the first case we observe a direct dependence of the current gain on the a-Si: H conductivity. In the second case, we observe a switching effect in the transistor conduction.