Surface recombination in GaAlAs/GaAs heterostructure bipolar transistors

The authors report unambiguous experimental evidence that surface recombination in n-p-n GaAlAs/GaAs heterostructure bipolar transistors changes from exp(qV/2kT) dependence at low currents to exp(qV/kT) dependence at high currents. They have used a current extraction technique to separate the kT current from the total base current in surface-passivated devices that use wide-gap p-GaAlAs as the surface of the extrinsic base to suppress electron injection. The kT dependence, which dominates at high bias, arises when the recombination rate is limited by availability of minority carriers at high surface-recombination velocities. To understand this phenomenon, the authors have applied an improved version of an existing two-dimensional simulator. The present model uses Fermi-Dirac statistics for the carriers and deep-level occupancy statistics that are self-consistent with the Shockley-Read-Hall recombination process