Resonance Raman Scattering in [111]-Oriented CdTe/CdMnTe Superlattices

Abstract

Cd_1-xMn_xTe alloys can be grown in zinc-blende structure up to a composition of х~0.7. The band gap of these crystals can be continuously tuned increasing the Mn composition.¹ The difference between the band gaps of CdTe and the ternary alloy provides the potential for the electronic confinement in superlattices (SL’s) and quantum wells. High quality SL’s based on Cdi_1-xMn_xTе have been grown in the last years using epitaxial techniques.2–4 The optical properties of these SI’s have been studied extensively in the literature.⁵ Resonance Raman Scattering (RRS) provides the link between electronic and lattice-dynamical properties: the energy dependence of the Raman efficiency is determined by the electron-phonon coupling and by band-structure parameters. Recent reviews deal with vibronic⁶ and electronic⁷ properties of semiconductor SI’s studied with RRS. The phonon spectra of Cd_1-xMn_xTe bulk crystals⁸ and CdTe/Cd_1-xMn_xTe superlattices^9–12 have been studied previously in the literature; these studies will be used here to compare new results in the SL’s. Usually, CdTe/Cd_1-xMn_xTe SL’s are grown on GaAs substrates. Two orientations of CdTe epitaxial films have been observed: (100)-CdTe parallel to (lOO)-GaAs¹³ or (111)-CdTe parallel to (100)-GaAs.14 Marked diferences between [lOO] and [ill] CdTe/Cd_1-xMn_xTe SL’s, attributed to the quality of the interfaces and to the presence of strain have been reported in the literature.^3,9,15 Here we present a RRS study on [111] SL’s which shows a similar behaviour to that observed in [001] superlattices.⁹