Spin-relaxation process of holes in type-II ${\mathrm{Al}}_{0.34}$${\mathrm{Ga}}_{0.66}$As/AlAs multiple quantum wells

We have measured the spin memory and the spin-relaxation times of holes in type-II quantum wells by means of pump-and-probe methods. The fast Γ-X interlayer scattering which is characteristic of type-II multiple quantum wells allows us to observe directly the hole spin-relaxation process. The hole spin relaxation is described by two decay components. The faster decay time ranges from 20 to 100 ps and depends on the number density of ‘‘antiparallel-spin’’ holes. This indicates that the scattering between up-spin holes and down-spin holes is the major spin-relaxation process of holes. The slower time component is about 20 ns, which is probably ascribed to the spin relaxation of localized holes in the well layers.