Photo-excited carrier relaxation dynamics in two-dimensional InSe flakes

摘要

Carrier relaxation dynamics of InSe flakes is investigated by using time-resolved pump-probe reflectivity measurement. The photocarriers associated with the P-xy orbital band-edge transition at 2.40 eV, which is coupled to the in-plane polarized light, is observed to possess a lifetime of similar to 19 ps at room temperature and similar to 99 ps at 10 K. The temperature and power dependent carrier lifetime suggests that Shockley-Read-Hall process is the dominant nonradiative recombination mechanism responsible for the carrier relaxation. In addition, the electron scattering with a 14.5meV optical phonon plays an active role in the carrier relaxation with increasing temperatures. A broad absorption around 1.65-1.90 eV is observed. The photocarriers associated with this broad transition show a long lifetime of similar to 200 ps that is nearly independent of temperature and photon energy. This is indicative of bound carriers by defects. Our experimental results provide essential information for the characteristics of carrier dynamics and defects in InSe flakes. The experimental findings are fundamentally important for further development of microelectronics and optoelectronics based on InSe.