PROFILE TAIL EFFECTS ON LOW-TEMPERATURE OPERATION OF SILICON BIPOLAR-TRANSISTORS

We present a detailed investigation, in the temperature range between 340 K and 80 K, of the static properties of advanced single-polysilico n bipolar transistors covering a wide range of base doping concentrati ons. Special attention is paid to the temperature dependence of the in trinsic current gain beta. We find that the rate of degradation of bet a with temperature below about 150 K is nearly independent of the peak or average base doping concentration. Our data do not match the conve ntional theory of the temperature dependence of beta using available b and-gap narrowing models for p-type silicon. We show that these, as we ll as other recently published related results, can be understood cons idering the importance of profile tail regions in controlling the oper ation of bipolar transistors at low temperature.