Abstract

While ultrafast optical techniques have been applied extensively to the study of hot electron dynamics in GaAs, there have been very few such studies of Si because conventional optical pumpprobe schemes are difficult to interpret for indirect gap materials. This is unfortunate since understanding hot electron dynamics in Si is key to predicting the behavior of state-of-the-art Si devices. Here we report the first direct subpicosecond (150 fsec) time-resolved measurement of the energy relaxation of optically excited electrons in Si. This is accomplished in a laser pump-probe format by analyzing the photoelectron spectrum generated by an ultrashort uv probe pulse. By this method, we obtain directly the time-evolution of the photo-excited electron distribution function (bulk and interface) in Si with 150 fsec resolution. These measurements would not be possible by either reflectivity/transmission or luminescence schemes.

© 1993 Optical Society of America