Magnetic-field-induced localization of carriers in ${\mathrm{Al}}_{0.25}{\mathrm{Ga}}_{0.75}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}\mathrm{A}\mathrm{s}$ multiple-quantum-well structures

The lowest-energy interband transitions in ${\mathrm{Al}}_{0.25}{\mathrm{Ga}}_{0.75}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}\mathrm{A}\mathrm{s}$ quantum wells are type-II, with electrons confined in the AlAs $X$-valley minima and holes in the ${\mathrm{Al}}_{0.25}{\mathrm{Ga}}_{0.75}\mathrm{As}$ layers. We have studied the intensity of these transitions in magnetic fields up to 30 T, in the 2–12-K temperature range. When the magnetic field is applied perpendicular to the structure layers the intensity of the various luminescence features associated with the type-II interband transitions decreases by an order of magnitude with increasing magnetic field. The field-induced intensity reduction is temperature sensitive and disappears for temperatures above 15 K. No change in the photoluminescence intensity is observed when the magnetic field is applied in the plane of the layers. The decrease in the recombination intensity is attributed to magnetic-field-induced carrier localization at the interfaces.