Subpicosecond hot carrier cooling in amorphous silicon

Measurements of the cooling rate of hot carriers in amorphous silicon are m ade with a two-pump, one-probe technique. Pump photons at 2 eV create free carriers and pump photons at 1.42 eV heat the carriers up to 1.2 eV/pair. T he experiment is simulated with a rate-equation model describing the energy transfer between a population of hot carriers and the lattice. An energy t ransfer rate proportional to the temperature difference is found to be cons istent with the experimental data. An energy transfer rate independent of t he temperature difference is inconsistent with the data. This contrasts wit h the situation in crystalline silicon and GaAs. The measured cooling time, 0.2 ps, is sufficient to explain the absence of avalanche effects in amorp hous silicon at fields below 10(6) V/cm. (C) 1998 American Institute of Phy sics. [S0021-8979(98)01621-1].