Femtosecond energy transfer in a-Si:H

Using femtosecond optical pulses to inject a carrier density greater than ${10}^{19}$ ${\mathrm{cm}}^{\mathrm{-}3}$, we observe that most of the carriers disappear within a few picoseconds. We show that this phenomenon results from nonradiative recombination, a process in which each electron-hole pair heats the lattice by giving up an energy equal to the pump photon energy. The delay between carrier recombination and lattice heating is estimated to be smaller than 100 fs, which may result from a very fast coupling between optical and acoustical phonons.