Hot-Carrier Thermalization in Amorphous Silicon

Thermalization of photoinduced carriers in $a$-Si and $a$-Si: H was studied with use of subpicosecond-pump and probe techniques with parallel and perpendicular polarizations. The underlying process was identified as hot-carrier absorption whose cross section increases with the carrier excess energy. The energy dissipation rate in $a$-Si is ≃0.5 eV/ps ($\simeq \hslash {{\nu }^2}_{\mathrm{phonon}}$) and is less than 0.1 eV/ps in $a$-Si: H; Fröhlich interaction with polar phonons can explain this smaller rate. A photoinduced dichroism associated with polarization memory was observed.