Spin-selective excitation spectroscopy of excitons and biexcitons in InxGa1-xAs quantum disks: Suppression of the spin-flip process in semiconductor zero-dimensional systems

The spin relaxation of photocreated excitons in InxGa1-xAs/Al(y)Ga(1-y)AS q uantum disks is investigated by microscope photoluminescence experiments un der spin-selective optical excitation. Complete quantization of the two-dim ensional energy structure of the quantum well into comb-shaped density of s tates results in inhibition of the elastic spin-flip processes, allowing on ly a simultaneous exchange of energy and momentum for spin relaxation. This slows down the spin flip in both the thermalization and recombination of e xciton and substantially increases the spin-relaxation time. For some excit on excited states, the spin-flip relaxation into another spin state is effi cient, thereby allowing the second photon absorption into a biexciton state even under the selective-spin excitation. [S0163-1829(99)00732-8].