K. Murayama

Electron time of flight experiment under high electric field in a-Si: H

Abstract Transit times in the time of flight experiment in a-Si: H has been studied over a range of electric field (1 × 10 4 ∼ 1.6 × 10 5 V/cm) and temperature (123 ∼ 173 K). We have found that the transit time decreases exponentially with increasing field at high fields. The exponential field dependence of the transit time obtained is consistent with a thermally activated hopping model rather than a multiple trapping model. The average distance between nearest neighbor hopping sites has been calculated to be 40 A.

Luminescence and absorption edge of a-Ge:H well layers in a-Si:H/a-Ge:H multilayers

Abstract The fundamental absorption edge spectra of a-Ge:H well layers with thickness of 1.0, 1.5, 2.5 and 4.0 nm in the a-Si:H/a-Ge:H multilayers have been obtained in the absorption coefficient range from 10 to 106 cm−1 by combining the luminescence excitation spectra with the optical transmission spectra at 15 K. The fundamental absorption edge spectra of the well layers have Urbach tails with slopes of about 50 meV. The luminescence decays of the a-Ge:H well layers have been measured in the time range from 10−7 to 10−2 s. The luminescence decays of the well layers at 15 K are described by a power law decay, t−δ, with δ∼1.2.

Temperature dependence of the photoluminescence in a-Si:H and a-As2S3

Abstract Temperature dependence of time-resolved luminescence spectra was measured for a -Si:H and a -As 2 S 3 to investigate thermalization processes of electron-hole pairs in the band tail. The shift of the luminescence peak as a function of temperature shows that the thermalization of electron-hole pairs in band tail states can be described by hopping rather than with the multiple-trapping model.

Optical properties of amorphous As2Se3As2S8 multilayers

Abstract Photoluminescence, excitation spectra and optical absorption spectra of amorphous chalcogenide multilayers of As 2 Se 3 As 2 S 8 were studied. Luminescence spectra of the multilayers were similar to those of the a-As2Se3 single layer. However, excitation spectra of multilayers were different from a-As2Se3, namely a blue shift of the spectra was observed for multilayers. Blue shift of the optical absorption spectra was observed with a decrease of the well-layer thickness. Experimental results are discussed using a configurational-coordinate diagram, where luminescence centers are localized and the extended states occupied by excited carriers are quantized.

Monte Carlo simulation of current induced by random walk on percolation cluster with fractal dimension

Abstract The current of particles induced by the random walk on percolation clusters, which were formed according to the site percolation process of a simple cubic lattice, was simulated by the Monte Carlo technique. The time dependence of the current obtained was quite similar to the typical transient current observed in time of flight experiment in various kinds of amorphous solids.

Thermalization gap of a-Si:H well layer in a-Si:H/a-Si3N4:H multilayers

Abstract The excitation energy dependence of the peak energy of the luminescence from a-Si:H well layers with thicknesses of 40, 5, 2.5, 1.3 and 0.5 nm in a-Si:H/a-Si 3 N 4 :H multilayers has been investigated at 15 K. The dependence shows that the luminescence in a-Si:H has the Stokes shift of 0.4 eV and the thermalization gap of the a-Si:H well layer obtained from the excitation energy dependence increases from 1.65 to 2.15 eV with decreasing well layer thickness. The dependence of the thermalization gap on the well layer thickness is explained from the hopping thermalization with the hopping length of about 2.5 nm at band tail localized states.

Phonon-assisted luminescence excitation in porous silicon

The bandgap of the luminescent Si structure in porous Si has been estimated to be about 2 eV from the excitation spectrum of the luminescence. The luminescence has been observed to be excited with the assistance of phonons in the light excitation with photon energies less than the bandgap. This excitation is explained by the phonon-assisted light excitation of the localized luminescence center with strong phonon-coupling in the Si structure.

Luminescence excitation assisted by phonons in porous silicon

The high-energy tail of the luminescence spectrum of porous Si excited with low photon energies has been observed to extend beyond the excitation energy. The temperature dependence of the luminescence intensity strongly depends on the excitation energy. These phenomena are explained in terms of phonon-assisted excitation of luminescence centers with strong phonon coupling.

Phonon interaction in the photoluminescence of a-Si:H/a-Si3N4:H multilayers

We have observed the excitation spectrum of the photoluminescence from a-Si:H well layers sandwiched with a-Si 3 N 4 :H and investigated the relation between the photoluminescence and the excitation spectrum. It is found that the photoluminescence process of bulk a-Si:H and a-Si:H well layers could be understood from the electron-phonon interaction model.

Anti-Stokes luminescence tail in porous Si

AbstractThe anti-Stokes luminescence tail of resonantly excited porous Si and its temperature evolution have been observed in theenergy range of 0.2 eV from the excitation energy. The activation energy calculated from the Arrhenius plot of the anti-Stokesluminescence intensity agrees with the anti-Stokes shift. This means that the intensity I asl –hn;E exc ;Tƒof the anti-Stokesluminescence with photon energy hnfrom the porous Si excited with light of energy E exc at temperature T can be describedby I asl –hn;E exc ;Tƒ‹f–hn;E exc ƒexp{ 2 –hn2 E exc ƒ=kT};where hn. E exc :The pre-exponential factor f–hn;E exc ƒis related tothe density of states of an electron–hole pair in an Si nanostructure with a bandgap E exc . The behavior of f–hn;E exc ƒhas beenfound to agree with the low photon energy part of the excitation spectrum of the luminescence. q 2001 Elsevier Science Ltd.All rights reserved. Keywords: A. Nanostructures; A. Semiconductors; D. Optical properties; D. PhononPACS: 71.15.pd; 71.20.eh