Time-resolved cathodoluminescence assessment of deep-level transitions in hydride-vapor-phase-epitaxy GaN

The temporal behavior of deep-level luminescence emissions in undoped hydride-vapor-phase-epitaxy GaN layers of different thicknesses has been investigated by time-resolved cathodoluminescence (TRCL). The complex nature of the yellow luminescence is revealed in the TRCL spectra by the presence of two bands peaked at 2.22 and 2.03 eV. A red band with a decay time of 700 mus, centered at about 1.85 eV, dominates spectra recorded for long delay times. Exponential transients with associated decay times of hundreds of mus were measured at 87 K for all the deep-level emissions found in the layers

Cathodoluminescence of electron irradiated opal-based nanocomposites

Synthetic opals infilled with silicon (opal-Si) and with Si and Pt (opal-Pt-Si) have been irradiated in a scanning electron microscope under high excitation conditions. Electron irradiation-induced changes in the morphology and luminescent defect structure of both types of nanocomposites were assessed by scanning electron microscopy and by cathodoluminescence (CL) microscopy and spectroscopy. Irradiation causes strong morphological changes in the ordered structure of the matrix and quenching of the nanocrystals-related CL emission in the opal-Si samples. On the contrary, such effects are not observed in the opal-Pt-Si nanocomposites. In both types of samples, electron irradiation induces the appearance of a CL band centered at 2.95 eV, attributed to complex centers involving oxygen vacancies in the silica spheres forming the matrix

Defect and nanocrystal cathodoluminescence of synthetic opals infilled with Si and Pt

Synthetic opals-composed of 250 nm amorphous silica spheres closed packed in a face centered cubic structure-have been infilled with silicon, platinum, and with Si and different Pt contents. The luminescent properties of these composites have been investigated by cathodoluminescence (CL) microscopy and spectroscopy. CL emission is influenced by the material used to infill the pores of the opal matrix. CL spectra of all the samples investigated show two well-known bands, associated with the defect structure of the silica spheres, centered at about 1.9 and 2.7 eV, respectively. Emission in the 2.15-2.45 eV range, particularly intense in opal-based composites with a high Pt content, is tentatively associated with SiO2 defects involving silicon clusters. A CL band peaked at about 3.4 eV as well as a band in the 1.50-1.75 eV range, whose peak position seems to be affected by the Pt content of the samples, are associated with the presence of Si nanocrystals. The behavior of these emissions suggests that both are related to defect states at the interface between Si nanocrystals and SiO2 forming the opal spheres