Intervalley scattering time in type-II ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/AlAs multiple quantum wells

Time-resolved photoluminescence (PL) experiments are reported on two ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/AlAs type-II multiple-quantum-well structures as a function of applied uniaxial stress parallel to the [110] direction, at T=4.5 K. The AlAs layer thicknesses of both samples are such that the ${\mathit{X}}_{\mathit{z}}$ valley is higher in energy than the ${\mathit{X}}_{\mathit{x}}$ and ${\mathit{X}}_{\mathit{y}}$ valleys. By using a time-windowing technique, the PL from both ${\mathit{X}}_{\mathit{z}}$ and lower-lying ${\mathit{X}}_{\mathit{x}}$ and ${\mathit{X}}_{\mathit{y}}$ states could be observed simultaneously providing a direct measure of the energy separation (ΔE) between the two valleys. With the application of a uniaxial stress, the time decay of the hot ${\mathit{X}}_{\mathit{z}}$ PL is then measured for various values of ΔE, providing intervalley ${\mathit{X}}_{\mathit{z}}$-${\mathit{X}}_{\mathit{x}}$ and ${\mathit{X}}_{\mathit{z}}$-${\mathit{X}}_{\mathit{y}}$ scattering times in the AlAs layers. The various mechanisms responsible for this relaxation process are identified.