Disorder-induced exciton localization in 2D wide-gap semiconductor solid solutions

Abstract

Exciton localization in quantum wells (QWs) formed by wide-gap solid solutions with isoelectronic substitution of ZnCdSe and InGaN is discussed. As a first step we discuss the microscopic mechanisms of exciton localization which are common for both 2D and bulk solid solutions. In most important for application solid solutions with good solubility, the exciton localization at small solution concentrations originates from the statistical clusters formed by a few atoms of the narrow-gap component. A theoretical model of absorption and photoluminescence (PL) spectra of diluted solutions is presented. The model explicitly accounts for the statistics of the substitutional atoms over the lattice sites. The parameters of the model can be determined from the analysis of the fine structure of PL spectra from the cluster states with different number of atoms. As a practical application of the model, the description of exciton spectra of diluted bulk InGaN solutions is presented. The effect of the lowering of dimensionality on exciton localization and the conditions for formation of 2D QWs from solid solutions are discussed. Experimental data on exciton localization in ZnCdSe/ZnSe QWs are presented. For diluted solutions the spectra can be described under the assumption of random distribution of Cd atoms along the QW plane. An increase of concentration due to the partial phase separation of ZnCdSe solutions leads to the formation of planar islands strongly enriched in Cd content. The results of optical study of the exciton states in the QWs with such island are reported.