Modelling of a new high current gain bipolar transistor with n-doped hydrogenated silicon emitter

The limitation of the maximum current gain attainable in a silicon bipolar transistor is due to many factors whose main effect is to prevent the blocking of minority carrier injection in the emitter. In the paper we show that blocking of minority carrier injection in the emitter, and hence a large increase of the current gain, can be achieved with a new type of npn bipolar transistor, where the emitter is made of n-doped hydrogenated amorphous silicon (a-Si: H). It is demonstrated that the very low mobility of carriers and the large bandgap (around 1.8 eV) in amorphous silicon are the two main factors involved in the improvement of the gain. The feasability and the potential interest of the device are studied in detail on the basis of the up-to-date known electrical properties of doped a-Si: H.