Photoreflectance characterization of an AlInAs/GaInAs heterojunction bipolar transistor structure with a chirped superlattice

We have measured the photoreflectance spectrum at 300 K from an AlInAs/GaIn As (lattice matched to InP) heterojunction bipolar transistor structure wit h a chirped superlattice (ChSl) grown by molecular-beam epitaxy. From the o bserved Franz-Keldysh oscillations we have evaluated the built-in dc electr ic fields and associated doping levels in the n-GaInAs collector and n-AlIn As emitter regions. The oscillatory signal originating from the ChSl is cau sed both by the uniform quasielectric and nonuniform space-charge fields in this region. (C) 2001 American Institute of Physics.