Optical Study of AlxGa1-xAs-AlAs Ternary Alloy Multi-Quantum-Well Structures around Two \({-}X\) Crossovers

We have studied the optical properties of Al x Ga 1- x As-AlAs ternary alloy multi-quantum-well structures around two \({-}X\) crossovers by means of photoluminescence and absorption saturation. In the photoluminescence, the peak due to the n =1 heavy exciton (\({-}\)) is observed for Al composition x from 0 up to 0.34. When x is 0.34 or more, another kind of the peak due to the \({-}X\) recombination (recombination between an X -electron in AIAs and a \(\)-hole in Al x Ga 1- x As) is observed in the low energy side, corresponding to the first \({-}X\) crossover. In the absorption saturation experiments, on the other hand, the saturation was observed in all the samples except the Al 0.51 Ga 0.49 As-AlAs sample corresponding to the second \({-}X\) crossover. The fact suggests that \(\)-electrons relax to the X-state is the Al x Ga 1- x As alloy very quickly compared with the other relaxation processes such as the \(-\) recombination in Al x Ga 1- x As and the transfer of a \(\)-electron in Al x Ga 1- x As to X -state in AlAs.