UP-CONVERTED PHOTOLIMINESCENCE IN ORDERED GaInP/GaAs HETEROINTERFACE AND ITS PRESSURE EFFECTS

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Quantum well (QW) emission from GaInP/GaAs structures grown by metalorganic vapor phase epitaxy can be masked by anomalous bands at 1.35〜1.46eV. We have studied partially ordered GaInP/GaAs QWs using up-converted photoluminescence (UPL) in which a sample emits photons with an energy higher than that of the excitation photon, together with the normal photoluminescence (PL) excited at a photon energy higher than that of the GaInP band gap and at high pressures.Using 2.54eV excitation the PL spectra from the sample with a thin GaP layer at both interfaces is dominated by the GaAs QW emission at 〜1.53eV. Spectra from the samples with only one GaP layer show no QW-related emission, instead a broad peak at 〜1.46eV and two weak peaks from the GaAs band-edge (1.51eV) and an impurity-related emission (1.49eV) are observed. Using high-pressure PL measurements, the 1.46eV peak can be attributed to spatially indirect transitions occurring in the vicinity of the interface. When excited with a photon energy of 1.58eV, which is well below the GaInP band gap but above the GaAs band gap, the 〜1.46eV emission band shows a drastic decrease in intensity while the weak near band-edge transitions become strong. In addition, all the samples with a thin GaP layer show UPL at 〜1.89eV. This energy is close to that of the normal PL of partially ordered GaInP. No UPL can be observed in the sample with two thin GaP layers, where the 〜1.46eV emission is absent. These results suggest that the presence of photo-generated electrons in the GaInP layer is greatly responsible for the observed 1.46eV emission and UPL.Theoretical arguments have suggested a type-II band alignment between GaInP and GaAs as the GaInP layer becomes more ordered. A two-step two-photon absorption mechanism for observing UPL has been discussed. Both the 〜1.46eV emission and the UPL observed in this work provide new evidence of a type II band alignment.