Profile Tail Effects on Low Temperature Operation of Silicon Bipolar Transistors

Abstract

We present a detailed investigation, in the temperature range between 340 K and 80 K, of the static properties of advanced single-polysilicon bipolar transistors covering a wide range of base doping concentrations. Special attention is paid to the temperature dependence of the intrinsic current gain β. We find that the rate of degradation of β with temperature below about 150 K is nearly independent of the peak or average base doping concentration. Our data do not match the conventional theory of the temperature dependence of β using available band-gap narrowing models for p-type silicon. We show that these, as well as other recently published related results, can be understood considering the importance of profile tail regions in controlling the operation of bipolar transistors at low temperature.