Dephasing of Excitons in Multiple Quantum Well Bragg Structures

Abstract

The recent progress in the development of ultrashort laser pulses enables observations of the coherent dynamics of excitons in quantum wells (QW) with less than 100 fs time resolution by transient degenerate-four-wave-mixing (DFWM). Such investigations have attracted rapidly growing attention as a powerful technique to explore nonlinear processes in semiconductors which may have enormous potential for future semiconductor device applications. Only very recently the role of many-body exciton-exciton interaction effects for the magnitude of the nonlinear optical response as well as for the optical dephasing rate has been studied in detail. So far, the discussion has been confined, however, to the coupling of excitons via Coulomb fields1. For GaAs multiple QW (MQW) samples, this interaction mechanism seems to be negligible for excitons excited in different wells if the barrier thickness exceeds values of 10–15 nm so that tunneling processes of carriers between the different wells can be excluded.