Localization of excited carriers in organometallic vapor-phase epitaxial grown ZnxCd1−xSe epilayers with partial existence of lateral compositionally modulated superlattice

Abstract

The structural and optical properties of organometallic vapor-phase epitaxial (OMVPE) grown ZnxCd1−xSe epilayers on the (001) InP substrate were studied by transmission electron microscopy (TEM) and photoluminescence (PL). The TEM results showed the spontaneous formation of compositionally modulated (CM) superlattices along the [110] direction with a period of ∼10–20 nm at some places in the epilayer. In the PL measurements, we found an anomalous red shift of PL with a decrease in temperature (from 170 K to 100 K) and a large blue shift up to 40 meV with an increase in excitation power. We suggested that the anomalous red shift of PL is caused by a localization of photo-excited carriers from places containing a normal random alloy to places containing a CM superlattice, which has a narrower bandgap, and the large blue shift is caused by a saturation of energy states in the CM superlattice under high excitation. The narrower bandgap of the CM superlattice is supported by a polarized PL study, where the low energy part of PL is strongly polarized along the [\(1\bar 10\)] direction, is consistent with the reduced symmetry of a CM superlattice. A two-level model was proposed to quantitatively account for the experimental observations.