Abstract

Picosecond relaxation processes of excitons are extensively studied in CuCl, CdSe and GaAs-AlAs MQW (multi-quantum well structures) by means of time-resolved induced absorption, luminescence and non-degenerate four-wave mixing. We have applied the picosecond time-resolved induced absorption and luminescence measurements to excitons in CuCl, CdSe and GaAs-AlAs MQW (Fig. 1). ^1-3) Aside from the typical nature of Wannier excitons in CuCl, excitons in CdSe and GaAs-AlAs MQW have distinct characters, such as strong piezoelctricity and two-dimensional disorder. The analysis of the experiments derives the distribution of excitons in the two-dimensional energy-time coordinates. Thus, energy relaxation processes of excitons in a variety of semiconductors are clearly visualized. Prior to energy relaxation, coherently generated excitons are considered to be dephased. Phase relaxation of excitons in CuCl is directly measured for the first time in the picosecond time domain by means of time-resolved non-degenerate four-wave mixing (Fig.2).⁴⁾ These new techniques will be demonstrated and the dephasing as well as energy relaxation mechanism of excitons and excitonic polaritons will be discussed.

© 1984 Optical Society of America