Photoreflectance characterization of interband transitions in GaAs/AlGaAs multiple quantum wells and modulation-doped heterojunctions

Abstract

The optical modulation technique of photoreflectance (PR) has been applied to characterize the interband transitions in GaAs/AlGaAs multiple quantum wells (MQW) and modulation-doped heterojunctions at room temperature. The spectra of the MQW show ‘‘derivativelike’’ reflectance features due to allowed interband transitions from heavy and light hole subbands to conduction subbands, and the E0(Γ8,v→Γ6,c) transitions of the AlGaAs layers. Our data are consistent with a square well calculation using a conduction-band offset of 60% of the band-gap discontinuity. For modulation-doped heterojunctions, a correlation is observed between a PR feature approximately 18 meV above the GaAs fundamental gap and the presence of a two-dimensional electron gas.