Abstract

The physics of highly excited semiconductors has recently been the subject of many studies, especially in connection with the problem of pulsed laser annealing. Careful experiments^1-3 have now been performed with the temporal resolution required to demonstrate that one single picosecond or femtosecond pulse can produce melting at the surface of silicon. Since the carrier relaxation time is very short (≲ 1 ps), melting occurs during illumination with ~30 ps pulses, such as those available from doubled Nd:YAG lasers. Unfortunately, because even the very dense electron-hole plasma (EHP) produced by a strong visible pulse will cause only a small change in the reflectivity of a probe beam (at 1.06 μm), up to densities ~10²¹ cm⁻³, it is difficult to use time-resolved reflection measurements to obtain detailed information on the dynamics of the very dense and hot EHP just before melting occurs. In this paper, we present results obtained using a novel technique that allows us to study in more detail the plasma close to but below the melting phase transition in Si and GaAs.

© 1984 Optical Society of America