Photoreflectance characterization of InP/GaAsSb double-heterojunction bipolar transistor epitaxial wafers

We report photoreflectance (PR) measurements of InP/GaAsSb double-heterojunction bipolar transistor epitaxial wafers grown by metalorganic vapor-phase epitaxy and discuss the correlation between the spectra and the electrical characteristics of the emitter-base (E/B) heterojunctions. The origin of Franz-Keldysh oscillations (FKOs) in the PR spectra was identified by step etching of the samples. The current-voltage characteristics of the E/B heterojunctions were examined by fabricating devices. FKOs from both the emitter and collector regions were observed in the wafers where the recombination forward current at the E/B heterojunction was suppressed. In contrast, when the recombination current was significant, no emitter-related FKOs were observed. The absence of the FKOs from the emitter indicates the high concentration of recombination centers at the EIB heterojunction. (c) 2005 American Vacuum Society.