Analysis of the temperature dependence of current gain in heterojunction bipolar transistors

An analytical description is developed which highlights the important physical parameters influencing the temperature dependence of the current gain in heterojunction bipolar transistors (HBTs). Each of the possible base current components is discussed and its relative importance to temperature dependence is assessed. The manifold nature of the contributions explains the widely different conditions under which negative differential resistance has been previously reported. Space charge region recombination is found to be the main contribution to temperature variation of current gain at low current densities. Factors affecting modern highly doped base devices at high current densities and elevated temperatures are reverse hole injection and base bulk recombination.