Raman and modulation spectroscopy at II-VI semiconductor interfaces

The structural and electronic properties of semiconductor interfaces crucia lly influence the behaviour of modern nanoscale heterostructures. We apply optical spectroscopy (Raman spectroscopy and electroreflectance (ER)) with special reference to the interface-induced vibronic signature and electroni c interband transitions in wide-band gap Ii-VT materials. This material sys tem allows the combination of materials with extremely different vibronic a nd electronic properties, which have to be matched at the interfaces. As ex amples we present the analysis of ZnSe/BeTe superlattices (SL) and CdSe mon olayers, embedded between BeTe barriers, grown on CaAs(100) substrates. Bot h systems exhibit type II electronic band alignment with a rather high vale nce band offset of about 1 eV and an electron confinement potential in the range of 2 eV. Since these II-VI compounds contain no common elements, two types of interface bond configurations are possible: either Be-Se or Zn-Te (Cd-Te). We show that the proper tics of the type-II spatially indirect tra nsition are completely governed by this interface layer. The normal and inv erted electronic interface signature can be addressed individually in ER by applying an external de electric field or by using polarised light with po larisation either along the [110] or [(1) over bar 10] direction. In additi on the chemical nature of the interface is analysed, using its phonon prope rties in Raman spectroscopy: They are completely altered for different inte rface bonding, conditions in the case of embedded monolayers. Moreover, the ER results from the epilayers: are also used for the deduction of the band offset at the interface substrate-epilayer and Schottky barrier of the out er interfaces (epilayer-metal).