Study of Ultrafast Photocarrier Dynamics in Polycrystalline Cdte Films Under Low Illumination

The photocarrier dynamics in polycrystalline CdTe films is closely related to device performance. However, the test results obtained at different illumination intensity may be different, and even significantly deviate from the ones in practical application environments. Here, the photocarrier dynamics in polycrystalline CdTe films deposited by thermal evaporation was studied through time-resolved transient absorption (TA) under different pump intensity. It was found that the behaviors of photocarriers in CdTe films is strongly dependent on the pump intensity. Under low pump intensity that close to operating environments, the lifetime of free carriers becomes extremely short compared to high intensity, which is interpreted as a rapid trapping of free carriers by defects. For low pump intensity, numerical fitting by a physical model with one defect level shows that the free carriers in band-edge can be rapidly trapped by defects within tens of picoseconds and then slowly recover to the ground state within several nanoseconds. Our results renewed the knowledge of photocarrier dynamics in polycrystalline CdTe films and develops a new characterization method for the preparation of high-quality films