Effects of electronic coupling on the band alignment of thin GaAs/AlAs quantum-well structures

We report the results of a systematic investigation of the effects of decreasing the AlAs layer thickness from 41 to 5 A{} on the band alignment of GaAs/AlAs quantum wells in which the GaAs thickness was kept constant at nominally 25 A{}. Combining the techniques of photoluminescence and photoluminescence excitation spectroscopy we have mapped out both the direct {Γ}-related band gap and the X-{Γ} band gap as a function of AlAs thickness. We observe a reversal of the band align- ment from the type-II to the type-I arrangement when the AlAs thickness is reduced below {~}13 A{}. In addition, we present further evidence which confirms that the type-II emission process is related to the Xz-{Γ} pseudodirect band gap. In the structures with very thin (10 A{}) AlAs layers we note a significant modification of the type-I excitation spectra where the n=1 exciton peak can be hundreds of times stronger than the apparent absorption in the continuum region.