Quantitative modelling of current gain and cut-off frequency at high injection levels at 77 and 300K in polysilicon emitter contact bipolar transistor

Abstract

Existed experiments and theories have demonstrated that the polysilicon emitter contact bipolar transistor (PET) is suitable for low-temperature operation. However, an overall theory for the current gain and the cut-off frequency of PET is still absent, particularly for the quantitative modelling at high injection levels. The paper presents the quantitative relationships between the current gain, the cut-off frequency and the collector current density at 77 K and 300 K. The main physical mechanisms for the current gain and the cut-off frequency at high injection levels are also analysed. Finally, the influence of the maximum base and emitter doping concentrations on the current gain, the base and emitter transit times in polysilicon emitter contact transistors is also analysed at low temperatures. These may provide a rational basis for the design of low-temperature bipolar transistors.