Line-shape analysis of Franz–Keldysh oscillations from a base-emitter junction in an InGaP/GaAs heterojunction bipolar transistor structure

We have investigated Franz–Keldysh oscillations (FKOs) from a base-emitter junction in an InGaP/GaAs heterojunction bipolar transistor structure using photoreflectance spectroscopy. The profiles of the FKOs originating from the InGaP emitter are compared with the line shapes calculated with the use of electro-optic functions. It is found that the line shape of the FKOs is remarkably affected by interference of probe light due to the multiple layer structure. Taking account of the interference effect, we have derived a novel analysis method for a convenient linear plot of the extremum positions of FKOs. The band-gap energy estimated with the present method well agrees with the band-gap energy obtained from the photoluminescence measurement of an InGaP/GaAs heterostructure for a reference.