Yasutoshi Kawaguchi

Temperature dependence of localized exciton transitions in AlGaN ternary alloy epitaxial layers

The optical properties of Ga-rich AlxGa1−xN (x=0.019, 0.038, 0.057, 0.077, and 0.092) ternary alloy epitaxial layers have been studied by means of temperature-dependent photoluminescence (PL) and time-resolved PL spectroscopy. The luminescence intensity of excitons in five epitaxial layers indicated a thermal quenching process with two activation energies. The two quenching activation energies were attributed to the delocalization of excitons and thermal dissociation of excitons. Anomalous temperature dependence of the PL peak energy was also observed in the epitaxial layers, which enabled the evaluation of the localization energy of the excitons. The localization energy increased as the 1.7th power of the PL linewidth, which reflected a broadening of the density of localized exciton states. In addition, the luminescence decay of the localized excitons for the five epitaxial layers became longer with decreasing emission energy. These observations suggest that the decay of excitons is caused not only by ra...

Localization-induced inhomogeneous screening of internal electric fields in AlGaN-based quantum wells

The influence of both localization and internal electric field on the microscopic photoluminescence (PL) properties of AlGaN-based quantum wells (QWs) has been studied by means of scanning near-field optical microscopy (SNOM). SNOM-PL images of three QWs with different well-layer thicknesses were measured under an illumination-collection mode. A correlation was observed between the PL intensity and the PL peak wavelength: a shorter-PL wavelength indicates a stronger intensity for a wider QW. The correlation is caused by an inhomogeneous screening of the internal electric field.

Biexciton luminescence from AlxGa1−xN epitaxial layers

Excitonic optical properties of Ga-rich AlxGa1−xN ternary alloy epitaxial layers (x=0.019, 0.038, 0.057, 0.077, and 0.092) have been studied by means of photoluminescence (PL) and time-resolved PL spectroscopy. The luminescence line due to radiative recombination of biexcitons was clearly observed for all of the five ternary alloy epitaxial layers with different Al compositions. The energy separation between exciton luminescence and biexciton luminescence increased with increasing Al composition, which indicated the increase in the binding energy of biexcitons in ternary alloys.

Population dynamics of localized biexcitons in AlxGa1−xN ternary alloys

Dynamical behavior of localized biexcitons in Ga-rich AlxGa1−xN ternary alloys has been studied by means of time-resolved luminescence spectroscopy. The time-dependent luminescence was analyzed using rate equations which were modified by considering the localization times of both the biexcitons and single excitons individually. The localization times of both biexcitons and single excitons became longer with increasing aluminum composition. On the other hand, the formation time of biexcitons from single excitons remained nearly unchanged. This observation indicated that the formation rate of biexcitons in the ternary alloys was independent of the localization depth of single excitons.