Abstract

Optical transitions in as-grown and annealed GaN${}_{0.02}$As${}_{0.98}$, Ga${}_{0.95}$In${}_{0.05}$N${}_{0.02}$As${}_{0.98}$, and GaN${}_{0.02}$As${}_{0.90}$Sb${}_{0.08}$ bulklike layers have been studied with photoreflectance (PR), photoluminescence (PL), and microphotoluminescence (\ensuremath{\mu}PL) in a broad range of temperatures. The exciton binding energy and the temperature dependence of the energy gap have been determined from PR measurements. In addition, the alloy-related broadening of optical transitions has been analyzed and compared for the three alloys. The largest alloy inhomogeneities have been observed for GaN${}_{0.02}$As${}_{0.90}$Sb${}_{0.08}$. In \ensuremath{\mu}PL spectra of GaN${}_{0.02}$As${}_{0.98}$ and Ga${}_{0.95}$In${}_{0.05}$N${}_{0.02}$As${}_{0.98}$ layers measured at low temperatures and low excitation conditions, sharp PL lines of 100--300-\ensuremath{\mu}eV widths have been clearly observed \ensuremath{\sim}10--20 meV below the energy gap of these alloys. Analyzing the temperature quenching of the sharp PL lines, they have been attributed to the recombination of localized excitons trapped at deep donor (acceptor)-like states. Such lines were not well resolved for GaN${}_{0.02}$As${}_{0.90}$Sb${}_{0.08}$ layers. The analysis of thermal quenching of localized exciton emission suggests that for this alloy excitons are localized mostly on alloy content fluctuations. With the increase in the excitation power an additional PL band has been observed in \ensuremath{\mu}PL spectra at the higher-energy side. This band corresponds to the optical transitions between delocalized states which are observed in photoreflectance spectra. The emission of localized excitons without resolved sharp lines has been also observed with macro-PL measurements at low temperatures. In addition, the donor trap--valence band (DT-VB) recombination has been identified for the three alloys in macro-PL spectra. It has been clearly observed that the intensity of DT-VB recombination is the weakest for GaN${}_{0.02}$As${}_{0.90}$Sb${}_{0.08}$ alloys whereas for GaN${}_{0.02}$As${}_{0.98}$ and Ga${}_{0.95}$In${}_{0.05}$N${}_{0.02}$As${}_{0.98}$ alloys it is very similar. The observed differences between the three alloys and the role of postgrowth annealing have been analyzed and discussed in the context of the influence of III-V host on alloy inhomogeneities, formation of native point defects in III-V-N alloys, and their influence on the optical quality of III-V-N alloys.

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