Type-II photoluminescence from GaP/AlP/GaP quantum wells

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Abstract
We have studied both continuous-wave and time-resolvedphotoluminescence from type-II GaP/AlP/GaP quantum wells with thickness of 1, 2, 3, 5, and 8 monolayers. Highly efficient no-phonon luminescence was observed at low temperatures, indicating long-lived temporal behavior. Photoluminescence results indicated that the lowest confined electron states in the AlP wells were the X z states. Nonexponential time decay of the no-phonon line suggested that the high efficiency of luminescence was due to the localization of indirect excitons by fluctuations in the potential at the interfaces. The effective interface roughness, which gave rise to the in-plane localization of the excitons, was much less than 1 atomic layer. A fit to the observed type-II transition energies gave a value for the conduction band offset of 0.38 eV for the GaP/AlP heterointerface.