The Use of Amorphous Silicon Emitters in Bipolar Transistors

For the first time an operating heterojunction bipolar silicon transistor has been realized with phosphorous doped amorphous silicon (a-Si) emitter. The deposition of a-Si is a relatively simple technique. The current gain (β) of 14 at a base Gummel Number (G.N.) of 1.35 1013 s/cm4 is higher than that obtained with normal diffused emitter bipolar transistors with the same G.N. for the base. This adds a degree of freedom to the design of bipolar structures according to the compromise between base resistance and current gain Crucial points that have to be looked at further are: interface recombination at the a-Si/c-Si transition and emitter resistance.