The model of hopping excitons in semiconductors proposed by Baranovskii et al (1998 Phys. Rev. B 58 13081) has been modified and applied to explain sharp lines observed in micro-photoluminescence (μ-PL) spectra of GaInNAs alloys and their changes with excitation power and temperature. Instead of two types of recombination centres (radiative and nonradiative centres) introduced by Baranovskii et alwe have proposed one kind of localization centre with radiative and nonradiative rates. Such a modification is justifiable due to our recent experimental observations for GaInNAs alloys and allows us to explain the fast thermal quenching of localized emission from this alloy. Our simulations clearly show that the individual sharp PL lines observed at low temperatures appear for this material due to exciton hopping between localization centres. Taking into account saturation effects and the exciton dissociation phenomenon, it has been shown that the observed changes in power- and temperature dependent μ-PL spectra can be excellently reproduced by the modified model.
The authors applied the temperature-dependent microphotoluminescence to study the thermal quenching of exciton lines related to localized emission from GaInNAs. It has been observed that the dispersion of localization energy is very strong (∼0–150 meV) whereas the activation energy of each individual line is the same within the experimental error (∼6 meV). This suggests that the main source of sharp line features are excitons localized on deep donor(acceptor)like states. At low temperatures these states can participate in radiative recombination due to the coulomb attraction between electrons and holes whereas at higher temperatures they still trap carriers but these carriers recombine nonradiatively.
Photoreflectance, photoluminescence, and microphotoluminescence study of optical transitionsbetween delocalized and localized states in 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 layers 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 (μPL) 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 μPL 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-μeV widths have been clearly observed ∼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 μPL 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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