Abstract

Quasi zero-dimensional quantum dots are supposed to be the ideal gain medium due to their discrete density of states. Recently, gain in quantum dots in the strong confinement regime (R<a_B) has been reported [1]. In contrast to bulk semiconductors, where plasma gain is the predominant process, a multi-level model taking biexciton and exciton states into account explains the stimulated emission process in these strongly quantum confined systems [2]. This model can be verified by investigating the dephasing processes in the gain region. As shown by Meissner and coworkers [3], the dephasing times in the gain region of an inverted bulk semiconductor show a substantial increase towards the Fermi edge (transparency point). This increase is due to the lack of final states at the Fermi edge in which carriers can scatter into. This singularity is a specific property of a plasma and should be observable in any system with plasma gain. Therefore, bulk-like quantum dots (R>a_B) should show an increase of T₂ towards the transparency point. In the multi-level gain of strongly confined quantum dots, however, the dephasing times should remain constant across the gain region because the biexciton and exciton levels are exposed to the same scattering background, consisting of LO phonons, surface states, and disorder.

© 1996 Optical Society of America