Intersubband and interminiband spectroscopy of doped and undoped CdS/ZnSe multiple quantum wells and superlattices -: art. no. 115334

In cubic CdS/ZnSe type-II heterostructures collective excitations have been studied using infrared spectroscopy. The CdS/ZnSe structures were grown by solid-source molecular-beam epitaxy on semi-insulating GaAs substrates. Highly n-type-doped multiple-quantum-well and superlattice samples show strong intersubband and interminiband absorption in the midinfrared. The validity of the polarization selection rule is verified experimentally. The CdS/ZnSe conduction band offset is determined using a combination of interband and intersubband spectroscopy. Measured transition energies agree well to model calculations if many-body effects and band nonparabolicity are included. Intensity-dependent pump and probe measurements on doped and undoped samples reveal a fast increase of the photoinduced absorption signal at low pump intensities. At high pump intensities the absorption signal saturates. This behavior is explained by the existence of a subgroup of long-lived photogenerated electron-hole pairs. An observed redshift of the photoinduced interminiband transitions is explained by filling of the lowest miniband. The effective electron mass of cubic CdS is determined from thick films using infrared reflection spectroscopy.