Abstract

The study of nonequilibrium carriers is essential for an understanding of the electronic properties of semiconductors and the physics of semiconductor devices. While great progress has been made in the measurement and understanding of hot carrier relaxation processes in crystalline semiconductors, little is known about the hot carrier cooling rates necessary for an understanding of carrier-phonon and carrier-carrier interactions in the extended states of amorphous semiconductors. Most experiments have been performed on the technologically important amorphous hydrogenated silicon (a-Si:H), a material which, because of its large optical gap (1.7eV), does not lend itself easily to the study of hot carrier dynamics with conventional femtosecond laser systems operating at or below photon energies in the spectral region surrounding 2eV. As a result, previous experiments [1] employing the pump-probe technique with 2eV excitation pulses as short as 100fsec have not revealed any evidence of hot carrier relaxation in a-Si:H, although indirect measurements [2] suggest that the carrier cooling rate is greater than leV/psec.

© 1992 The Author(s)