Recombination kinetics of Te isoelectronic centers in ZnSTe

The recombination kinetics of Te isoelectronic centers in $ZnS1−xTex$ $(0.0065⩽x⩽0.85)$ alloys is studied by time-resolved photoluminescence (TRPL) at low temperature. The measured radiative recombination lifetimes of different Te bound exciton states are quite different, varying from a few nanoseconds to tens of nanosecond. As the bound exciton state evolves from a single Te impurity $(Te1)$ to larger Te clusters $(Ten,n=2,3,4)$⁠, the recombination lifetime increases. It reaches maximum $(∼40ns)$ for the $Te4$ bound states at $x=0.155$⁠. The increase of the exciton lifetime is attributed to the increasing exciton localization effect caused by larger localization potential. In the large Te composition range $(x>0.155)$⁠, the exciton recombination lifetime decreases monotonically with Te composition. It is mainly due to the hybridization between the Te localized states and the host valence band states. The composition dependences of the exciton binding energy and the photoluminescence (PL) line width show the similar tendency that further support the localization picture obtained from the TRPL measurement.