Picosecond Photoemission Studies of Laser-Induced Phase Transitions in Silicon

Abstract

Quantitative evaluation of the energy transfer processes from optically excited electron-hole pairs to lattice phonons has become an important issue in the study of laser-induced phenomena at the surface of semiconductors. This goal has been mostly pursued through time-resolved optical diagnostics. Electron-hole plasma kinetics and evolution of the lattice temperature have been explored in a wide range of time scales [1]. However, lack of information on the energy dependence of several critical parameters in the dielectric response of the medium prevent an evaluation of the energy content of the carriers with these methods. The second question of major importance for the understanding of the laser-induced phase transitions is whether the solid state lattice structure becomes unstable by electronic or vibronic excitation. Even with ps laser excitation, however, strong evidence for an ultrafast energy transfer from the plasma to the lattice phonons has been found [2] and the validity of the thermal model confirmed.