cw photoluminescence determination of thermally activated fastX→Γ interlayer electron scattering in type-II GaAs/AlAs superlattices

We have observed dominant type-I photoluminescence from type-II GaAs/AlAs superlattices at temperatures higher than 150 K. The measured type-I to type-II photoluminescence intensity ratio at various temperatures is quantitatively described by a three-level rate-equation model. Our results demonstrate the importance of the X{→}{Γ} real-space charge-transfer (RSCT) process, i.e., the interlayer electron scattering from the AlAs X valleys back to the GaAs {Γ} minimum, which leads to the thermally activated type-I emission in type-II structures. Furthermore, we have determined the temperature dependence of this X{→}{Γ} interlayer electron scattering from 2 to 300 K. The X{→}{Γ} RSCT time is determined to be about 20 ps at T=300 K. Finally, our results demonstrate that cw PL measurements are useful in determining ultrafast (fs) scattering times.