With the development of high reliability electronic techniques

it is needed that current gain HFE of the silicon bipolar transistors has very low positive temperature coefficient.The bandgap narrowing effect resulted from the emitter heavy doping is the main reason of the high positive temperature cofficient of current gain in the common silicon bipolar transistors. In order to reduce this positive temperature cofficient

some novel structures such as polysilicon emitter contact

polysilicon emitter and amorphous silicon emitter are adopted. The experimental results indicate that the high temperature rising rate and the low temperature falling rate of HFE in these novel transistors are all less than 20%

and some are even less than 10%.