Currents and current gain analysis of passivated heterojunction bipolar transistors (HBT)

In this paper, we investigate the effect of the effective interface velocities on the currents, and the current gain of arbitrary base doping and different types of level injection in the base of a heterojunction bipolar transistors (HBT). It is shown that the space-charge region recombination current and the collector current are strong functions of the effective interface velocities and the thermionic flux. An expression of the effective interface velocities and the carrier boundary conditions of the HBT are derived. The effect of the thermionic emission flux on the quasi-Fermi level discontinuity is studied, and an expression of the quasi-Fermi level discontinuity is derived and shown to be function of the interface velocities and the space-charge recombination current. An expression of the current gain of an HBT is derived. The calculated current gain is in excellent agreement with other reported experimental results