Optical Signatures of Impurity–Impurity Interactions in Copper Containing II–VI Alloy Semiconductors

We study the optical properties of copper containing II–VI alloy quantum dots (Cu_<i>x</i>Zn_<i>y</i>Cd_{1–<i>x</i>–<i>y</i>}Se). Copper mole fractions within the host are varied from 0.001 to 0.35. No impurity phases are observed over this composition range, and the formation of secondary phases of copper selenide are observed only at <i>x</i>_Cu > 0.45. The optical absorption and emission spectra of these materials are observed to be a strong function of <i>x</i>_Cu, and provide information regarding composition induced impurity-impurity interactions. In particular, the integrated cross section of optical absorption per copper atom changes sharply (from 1 × 10 ^–2 nm³ to 4 × 10 ^–2 nm³) at <i>x</i>_Cu = 0.12, suggesting a composition induced change in local electronic structure. These materials may serve as model systems to understand the electronic structure of I–III–VI₂ semiconductor compounds