ABSTRACT
Two different graded-gap superlattices (SLs) have been realized and investigated by photocurrent (PC), electroreflectance (ER) and photoluminescence (PL) spectroscopy. The first SL is compositionally graded, while the second system consists of layers with different well and barrier thicknesses. In contrast to the compositionally graded SL, the PC spectra of the second system are dominated by excitonic effects. The formation of a miniband at finite electric fields can be clearly observed in the ER-spectra of the compositionally graded SL.
