Carrier dynamics in monolayer WS2/GaAs heterostructures

We investigate the carrier dynamics in monolayer-WS2/SiO2 and WS2/GaAs heterojunctions using time-resolved photoluminescence in this study. The exciton lifetime and radiative lifetime for WS2/GaAs sample were determined to be 497 ps and 46 ns, respectively, which are much larger than those of the WS2/SiO2 sample. Then the energy band structure at the WS2/GaAs heterojunction was explored using x-ray photoelectron spectroscopy. A type-II band alignment was confirmed at the interface with the conduction band offset about 1.415 eV and valence band offset 0.55 eV, which was further proved by ultraviolet photoelectron spectroscopy. As a result, the WS2/GaAs junction facilitated electron and hole separation by the aid of built-in field, and in turn enlarged the carrier lifetime. This work provided a promising integration of 2D materials with traditional bulk semiconductors for future high efficiency, highly reliable applications in photonic and optoelectronic devices.