Calculation and analysis of dc parameters in silicon heterojunction bipolar transistors with amorphous emitters at low temperatures

Abstract

The low temperature properties of silicon heterojunction bipolar transistors with amorphous emitters are studied. It is indicated that the current gain, HFE, has a positive temperature coefficient and falls with increasing base concentration, NB, at room temperature and low temperatures, differing from conventional silicon bipolar transistors. HFE increases with increasing applied voltage across the collector-base junction, because of the avalanche multiplication effect in the collector-base junction at low temperatures. The collector current, IC, increases as NB increases at low temperatures, which is entirely opposite to the result at room temperature. It is finally concluded that the value of HFE of this device at low temperatures is adequate for most applications.