Spin-polarized excitons in pseudomorphic, strained ${\mathrm{In}}_{0.16}$${\mathrm{Ga}}_{0.84}$As/${\mathrm{Al}}_{0.29}$${\mathrm{Ga}}_{0.71}$As quantum wells on a GaAs substrate

Circularly polarized excitation light from a tunable Ti-doped sapphire laser has been used to produce spin-polarized excitons in strained, pseudomorphic ${\mathrm{In}}_{0.16}$${\mathrm{Ga}}_{0.84}$As/${\mathrm{Al}}_{0.29}$${\mathrm{Ga}}_{0.71}$As quantum wells (QW’s) grown on GaAs substrates. By analyzing the degree of circular polarization of the exciton luminescence and by studying the depolarization effect of a transverse magnetic field, the optical lifetime and the spin-relaxation time of excited carriers can be determined in relatively wide wells. We further show that circular excitation offers a relatively simple means to discriminate unambiguously between light- and heavy-hole excitons. We have thus made measurements that yield optically determined band offsets for the QW system under investigation.