Abstract

In narrow GaAs/ AIAs type-II multiple quantum wells (MQWs), electrons initially optically excited in the GaAs layers transfer on a subpicosecond time scale to the lower-lying indirect energy level (X-valley) in the AIAs layers,¹ resulting in electrons and holes separated in real as well as reciprocal spaces. We refer to the difference between the GaAs T- valley and the AIAs X-valley in the conduction band as the T-X splitting. Our type-II samples, which were grown by molecular beam epitaxy, have a T-X splitting of ≈ 85 meV obtained from low-temperature photoluminescence. For the flatband case, the electronic states at the AIAs X-valley that are energetically below the GaAs T-valley must first be filled before gain can be observed at the direct transition. Using amplified 100-fs optical pulses to highly excite our MQW samples, we have observed gain in GaAs/AIAs type-II MQWs (see Fig. 1) using a time-correlated broadband continuum probe.

© 1992 Optical Society of America