Defect-Induced Ultrafast Nonadiabatic Electron-Hole Recombination Process in PtSe Monolayer.

Defects are inevitable in two-dimensional materials due to the growth condition, which results in many unexpected changes in materials' properties. Here, we have mainly discussed the nonradiative recombination dynamics of PtSe monolayer without/with native point defects. Based on first-principles calculations, a shallow p-type defect state is introduced by a Se antisite, and three n-type defect states with a double-degenerate shallow defect state and a deep defect state are introduced by a Se vacancy. Significantly, these defect states couple strongly to the pristine valence band maximum and lead to the enhancement of the in-plane vibrational E mode. Both factors appreciably increase the nonadiabatic coupling, accelerating the electron-hole recombination process. An explanation of PtSe-based photodetectors with the slow response, compared to conventional devices, is provided by studying this nonradiative transitions process.