Abstract

The technique known as population mixing or picosecond excitation correlation was introduced in 1981¹ and was since then widely employed to study carrier dynamics in semi-conductor materials.^2-4 The variation in the delay between the two trains of pump pulses often yields symmetric correlation photoluminescence (PL) signals that decay, maintaining always the same sign, such as shown in Fig. 1(a). This type of PL correlation signals, which are of simple interpretation, have often appeared in the literature and the signal decay rate has been used to measure carrier recombination¹ and tunneling times.³ However, the changes in slope and sign of the signal that we observe depending on the power of the excitation and the energy range of the PL signal (Figs. 1 (b-d)), have remained for the most part absent in the literature, perhaps because of its more difficult interpretation. Such significant changes in the signal characteristics merit study because they can provide valuable information on processes occurring in photoexcited materials.

© 1993 Optical Society of America