Ultrafast Time-Resolved Photoluminescence of Zn-Se-Te Multilayers with Type-II ZnTe/ZnSe Quantum Dots

摘要

Time-resolved photoluminescence (TRPL) across the full spectrum of a 240 layer ZnTe/ZnSe super-lattice structure has been performed using a femtosecond Ti-Sapphire laser and a streak camera system for detection. A significant change of the PL lifetime is observed across the emission spectrum decreasing smoothly from ～ 100 ns at 2.35 eV, to less than a few nanoseconds at 2.8 eV. The increase of the PL lifetime in the low energy region of the emission spectrum is strong evidence to support the formation of type-II quantum dots (QDs) from excitons bound to clusters of Te-atoms. In such QDs the confined holes and the free electrons are spatially separated, thus increasing the radiative lifetime. This result is consistent with recent photoluminescence (PL) measurements in which evidence of the combined contribution of excitons bound isoelectronically to Te-atoms, and type-II QDs was observed.