Origin of high offset voltage in an AlGaAs/GaAs heterojunction bipolar transistor

The high offset voltage of an Npn AlGaAs/GaAs heterojunction bipolar transistor prepared by liquid phase epitaxy is proved to be equal to the turn-on voltage difference between emitter-base heterojunction and base-collector homojunction. The potential spike at the emitter-base heterointerface is experimentally confirmed by observing an activated transport process and a reachthrough effect under reverse operation. It is believed that the electron thermionic emission process plays an important role in determining the p-n junction I-V characteristics.