Abstract
AbstractNear band gap luminescence in bulk-grown semi-insulating GaAs is excited in a two step process via the EL2 defect. While the conventionally excited photoluminescence of our samples is dominated by conduction band to acceptor transitions, the upconversion process selectively excites donor acceptor pair transitions. Illumination near the maximum of the EL2- photoquenching band at 1064 nm leads to a complete disappearance of the so called upconversion photoluminescence (UPL). Excitation with light of shorter wavelengths however only partially quenches the UPL. Excitation between 850nm and 900nm completely regenerates the UPL. The characteristic photorecovery transients of the UPL are described by the EL2 regeneration mechanism via the population of the acceptor level of the metastable EL2 by hot electrons. The recovery of the EL2 by simultaneous illumination with above and below band gap light enables the observation of UPL at wavelengths, where the EL2-defect would otherwise be rapidly quenched. Under these conditions we observe a remarkable increase of the UPL-efficiency.
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