Long spin-flip time and large Zeeman splitting of holes in type-II ZnTe/ZnSe submonolayer quantum dots
H Ji, S Dhomkar, R. Wu, J Ludwig, Z Lu, D Smirnov, M C. Tamargo, Garnett W. Bryant, I L. Kuskovsky
The Zeeman splitting and degree of circular polarization (DCP) of photoluminescence (PL) from type-II submonolayer ZnTe/ZnSe quantum dots (QDs) have been investigated in magnetic fields up to 18 T. To explain observed relative intensities and energy positions of the σ+ and the σ- PL, a model with ultra-long spin-flip time of holes confined to submonolayer QDs is proposed. The g-factor of electrons, located in the ZnSe barriers, was obtain from fitting the temperature dependence of the DCP, and its value is in the excellent agreement with that of bulk ZnSe. The g-factor of the QD-bound type-II excitons was extracted by analyzing the Zeeman splitting, from which the g-factor of holes confined within submonolayer ZnTe QDs was found to be ~ 2.65. This value is considerably larger than that in bulk ZnTe. Tight-binding calculations were further employed to understand the origin of such an increase. The calculations showed that enhancement of hole g-factor is mostly caused by a reduced orbital contribution to Zeeman splitting due to submonolayer thickness of these QDs.