Intersubband and interminiband transitions in CdS/ZnSe heterostructures

We report on the first investigation of intersubband and interminiband transitions in CdS/ZnSe multiple quantum wells and superlattices. The cubic heterostructures with type II band alignment were grown by molecular beam epitaxy on semi-insulating GaAs (0 0 1) substrates using CdS and ZnSe compound sources. The transmission spectra of n-type doped CdS/ZnSe heterostructures recorded in waveguide geometry show strong absorption lines in the mid-infrared. These absorption structures are attributed to intersubband (interminiband) transitions from the first to the second subband (miniband). The strong absorption is a direct consequence of the different refraction indices of the GaAs substrate and the wide-gap II–VI semiconductor heterostructure. Furthermore, first results of pump-probe experiments performed on lightly doped and undoped multiple quantum wells are presented. The photoinduced absorption was studied in dependence on the laser power. Thereby, the pump intensity was varied over three orders of magnitude.