Kazuro Murayama

A universal distribution function of relaxation in amorphous materials

Abstract A universal distribution function of the relaxation time is proposed for the non-exponential relaxation process in amorphous materials. This function contains the usual exponential decay, the extended exponential decay (Williams-Watts decay) and the power law decay as the special case of the function. Photoluminescence and dielectric relaxation observed in the amorphous materials is well reproduced by this function on the time dependence of the relaxation process and its Fourier transform in the wide range of time and frequency for many kinds of amorphous materials.

Luminescence and optically detected ESR in a-As2S3

Abstract Luminescence with decay time of about 10 nsec and the Stokes-shift of about 0.84 eV was found in a-As2S3 by the excitation at the absorption edge at 4.2 K. The peak position of the luminescence depended on the excitation energy and the luminescence remembered the polarization of light of the excitation. The experimental data can be explained by assuming that the luminescence and the absorption edge are due to localized excitons. Photo-structural change is discussed according to the exciton model. In addition, ESR of centers of the luminescence observed by Kolomiets et al. was optically detected.

Luminescence with short decay time in arsenic chalcogenide glasses

Abstract Luminescence with decay time of about 10 nsec or shorter was found in a−As2S3 at 4.2 K on the high energy side of the luminescence observed by Kolomiets et al. From the dependence of the emission spectra on the excitation energy, it is interpreted as being due to the recombination of localized excitons.

INTERRELATION BETWEEN GLASS TRANSITION AND REVERSIBLE PHOTOSTRUCTURAL CHANGE IN a-As2S3

Abstract The optical absorption edge has been observed to make a parallel shift to lower energy in a -As 2 S 3 as the glass transition temperature, T g , increases. The structural difference corresponding to different T g and reversible photostructural change give the same linear relation between the edge shift and the volume change. The saturated position of the edge after long time illumination or annealing is determined only by the condition of last treatment and is independent of previous history. These results suggest that both structural changes are of the same kind and that in the glass there exists an equilibrium state under illumination, if crystallization is avoided.

Photoluminescence Decay in Amorphous As2S3

The decay of the intensity of the luminescence in a-As2S3 with the energies of 1.16 and 1.57 eV was measured from 10-8 sec to 2×10-3 sec at 4.2 K. The shape of the decay curves shows three kinds of luminescence whose intensity decays according to the empirical decay function (f(t)=tn-1exp -(t/τ)n) with effective decay times (τ) of 2×10-8, 2×10-6 and 2×10-4 sec. Each luminescence process is discussed in this paper.

Change in optical anisotropy of localized states associated with reversible photostructural change in a-As2S3 films

Abstract In annealed As 2 S 3 films, band-gap illumination induces red-shift of optical absorption edge and increase of polarization memory of photoluminescence. In the case of illumination with linearly polarized light, anisotropy is induced in both. From dependence of the edge shift, the anisotropy of the absorption edge and the increase of polarization memory on the illumination conditions (temperature, photon energy and intensity), it was found that there was a strong correlation between the latter two but the edge shift had no correlation with the latters. The latter two reflect the increase of the optical anisotropy of the localized states and the reorientation of the anisotropy axes to the direction perpendicular to the polarization vector of the illumination light, but the bulk change in the structure gives the edge shift.

Time dependence of the polarization of the luminescence in chalcogenide glasses

Abstract Time dependence of the polarization of the luminescence with polarized exciting light and its temperature dependence were observed in chalcogenide glasses. The experimental data can be analyzed with a model based on localized excitons in a fluctuating potential due to random structure of the glasses.

Photoluminescence decay affected by hopping in band tail in amorphous semiconductors

Abstract Photoluminescence decay was observed at various temperatures in amorphous hydrogenated Si. The decay had the t−1.2∼−1.3 long time behavior at the high temperature. This decay was concluded to arise from the combination of the electron-hole pair recombination and the hopping of carriers on the fractal structure formed of localized sites of band tail. The fractal dimension was estimated to be about 2.5.

Photoluminescence decay affected by variable range hopping in band tail in amorphous As2S3

Abstract Photoluminescence decay was observed with various excitation energies and at various temperatures in amorphous As2S3. The decay at high temperature or with the high excitation energy had the t -3 2 long time behavior. This decay is concluded to arise from the combination of the tunneling recombination and the variable range hopping of carriers in the band tail.

Time-resolved photoluminescence in chalcogenide glasses

Abstract The time resolved spectroscopy of the photoluminescence with pulse-dye-laser excitation supplied the direct evidence of the strong electron-phonon interaction and the distributed localized states at band edges and the important information of mobility edge in chalcogenide glasses. The excitation energy dependence of the time resolved photoluminescence indicated that a-As 2 S 3 and a-GeSe 2 at 4.2 K had the mobility gaps of 2.6 eV and 2.25 eV, respectively.