HOT CARRIER RELAXATION AND RECOMBINATION IN AMORPHOUS-SEMICONDUCTORS

We report the results of femtosecond optical measurements following in jection of a very large density (> 10(19) cm-3) of carriers with 100 f s 2 eV pulses in a-Si:H. We measure the momentum scattering time of th e free carriers (< 1 fs), the thermalization rate of hot carriers (gre ater-than-or-similar-to 1 eV ps-1), the non-radiative carrier recombin ation lifetime (1-10 ps), and the decay time of optic phonons into aco ustic phonons (less-than-or-similar-to 100 fs). The lack of momentum c onservation in amorphous materials is responsible for the much shorter characteristic times in a-Si:H than in a typical direct-gap semicondu ctor such as GaAs.