OPTICAL-PROPERTIES OF MBE-GROWN ZNTE ON GAAS - EFFECTS OF A ZNSE BUFFER LAYER

Effects of a ZnSe buffer layer on the optical properties in ZnTe on Ga As grown by molecular beam epitaxy (MBE) are investigated by photolumi nescence (PL) and Raman scattering. From PL results an improvement of crystallinity of ZnTe films is recognized as the thickness of the ZnSe buffer layer increases. This is explained well by an exponential incr ease of the ratio of neutral acceptor-exciton complex to deep level em ission with increasing ZnSe buffer layer thickness. Raman scattering r esults show an elongation of the ZnSe lattice by expansion due to acco modation of the ZnTe lattice. The large critical thickness of ZnTe/ZnS e is estimated experimentally to be about 30 nm in MBE growth on GaAs because of similar electronegativity in growth of ZnTe on ZnSe. The re sult obtained from the temperature dependence of LO phonon frequencies supports also an expansion of the ZnSe lattice obtained by Raman scat tering.