Optical characterization and thermal dissociation of bound excitons inCdSexTe1−x

A detailed spectroscopy study of Te-rich ${\mathrm{CdSe}}_{\mathrm{x}}$ ${\mathrm{Te}}_{1\mathrm{-}\mathrm{x}}$ has been performed. The position of the free exciton and the optical band gap in ${\mathrm{CdSe}}_{0.04}$ ${\mathrm{Te}}_{0.96}$ are obtained from luminescence and reflectivity measurements. The binding energies of excitons to acceptors and donors are deduced from the energies of the photoluminescence maxima. The dissociation mechanisms of these complexes are studied by measuring the temperature dependence of the integrated emission. Two activated dissociation processes are observed for excitons bound to residual donors in both alloys studied, ${\mathrm{CdSe}}_{0.04}$ ${\mathrm{Te}}_{0.96}$ and ${\mathrm{CdSe}}_{0.20}$ ${\mathrm{Te}}_{0.80}$. At low temperature, the $D^0$X emission is quenched by the dissociation into a free exciton, whereas at higher temperature the dominant process corresponds to the dissociation of $D^0$X into one free electron and one free hole. For excitons bound to neutral acceptors in ${\mathrm{CdSe}}_{0.04}$ ${\mathrm{Te}}_{0.96}$, only one activation energy (dissociation into a free exciton) is obtained from the $A^0$X emission intensity variation versus temperature. Our results are compared to those obtained in ${\mathrm{Cd}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Zn}}_{\mathrm{x}}$Te and ${\mathrm{CdS}}_{\mathrm{x}}$ ${\mathrm{Se}}_{1\mathrm{-}\mathrm{x}}$ alloys.