Luminescence far above the excitation energy is observed at GaAs- GaInP2 interfaces. The intensity of this up-converted signal varies superlinearly with excitation density. Up-converted photoluminescence excitation spectroscopy shows that the signal disappears if the excitation energy is tuned below the GaAs band gap. It is concluded that cold Auger processes and the presence of metastable states in the GaInP2, induced by residual CuPt ordering, cause this nonlinear effect at these type I interfaces.
A detailed study of the photoluminescence (PL) and photoluminescence excitation (PLE) properties of Al0.48In0.52As is presented. A PL linewidth of 13 meV and a Stokes shift of only 9 meV at 4.2 K both indicate that the effect of clustering is minimal in our samples. The Stokes shift is three times lower than the lowest reported in the literature. No shift was observed in the position of the PL peak with changing excitation intensity. Both the PL energy and intensity showed anomalous temperature behavior: The energy first decreased, then increased, and finally decreased again with increasing temperature (the so-called inverted S shape); the intensity showed a temperature dependence similar to that of amorphous semiconductors and disordered superlattices. These two phenomena suggest strong localization of carriers in Al0.48In0.52As, even when the effect of clustering is minimal. The PLE spectra showed excitonic enhancement only above 40 K. The first observation of phonons with PL is reported in Al0.48In0.52As. Energies of 29.6 and 45.9 meV were measured for the InAs-like and the AlAs-like LO phonons, respectively. These phonons could only be detected below 40 K, which, on the basis of selection rules for LO phonon scattering, confirms the localized nature of the luminescence.
Efficient, low-temperature conversion of infrared light into visible light ͑red, orange, green͒ is reported at single heterojunctions and undoped quantum wells of GaAs and ordered Al x Ga 1Ϫx InP 2 ; an increase in photon energy of 700 meV is obtained. The signal originates from the high-band-gap layers and disappears only if the excitation energy is tuned below the GaAs band gap. The intensity of the up-converted photoluminescence ͑PL͒ is found to decrease significantly slower with increasing temperature than that of the regular PL and it remains observable up to 200 K. Interface-induced cold Auger processes along with the presence of trapped states for both electrons and holes in these ordered alloys account for this nonlinear mechanism. A colinear double-beam experiment confirms this.
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