A comprehensive optical characterization method for high-performance n-p-n AlGaAs-GaAs heterojunction bipolar transistors

We report a comprehensive optical wafer evaluation technique for C-doped n-p-n heterojunction bipolar transistors (HBT) using low temperature photoluminescence spectroscopy. The correspondence between the optically determined parameters at the wafer level and the electrical device parameters is demonstrated. The hole density in the base of transistor structures was obtained from optical transitions in the p⁺-GaAs layer exploiting the bandgap narrowing effect. Furthermore, our experimental studies, which combine optical and electrical measurements, show that a photovoltaic effect observed in the optical spectrum measures the strength of carrier recombination processes in the emitter-base heterojunction region. Because interface recombination strongly affects the dc current gain of these devices, photoluminescence spectroscopy of epitaxial wafers provides critical information on HBT device parameters prior to device fabrication