Ultrafast dynamics of hot carriers in bulk semiconductors and in accumulation layer: energy transfer and screening effects.

Electron-phonon coupling determines the charge transport properties in pure materials as well as the relaxation dynamics of photoexcited carriers.  A computational method based on density functional theory (DFT) and on interpolation of the electron-phonon matrix elements in Wannier space allowed to successfully interpret the dynamics of photoexcited electron relaxation in several semiconductors, such as GaAs, Si, InSe, in good agreement with two-photon photoemission experiments.

We  will present  our  results on  the  photoexcited electron  relaxation  in InSe, a quasi-2D material which was shown recently to have potential interest for optoelectronics.  We will discuss our results on the relaxation dynamics and screening of the electron-phonon interaction in doped InSe. The influence of the two-dimensional (2D) electron gas,  created on the InSe surface by Cs deposition, on the relaxation dynamics of photoexcited electrons, was stydied by photoemission spectroscopy and by ab initio calculations. We have shown that the remote coupling with the bulk phonons persists even in the case of complete thermalisation of the photoexcited electrons with the 2D gas, and that the  coupling of electrons with polar optical phonons is not completely screened even at high Cs concentrations.