Thermal conductivity of amorphous As2Se3 with copper

Phonon thermal conductivity of amorphous As₂Se₃ with the content of copper is studied in the temperature range between 100 and 300°K. The mean free path of phonons is calculated and using the measured values of the velocity of the longitudinal acoustic waves, microhardness, softening temperature and of the density, the possibility of the arrangement of the basic structure units of the semiconducting As₂Se₃ glass is discussed.Thanks are due to Mrs J. Trepeová for the measurement of the thermal conductivity of the samples.     

Experimental study and configurational-coordinate model for photo-induced effects in amorphous As2Se3 films

The optical absorption of As₂Se₃ thin films is studied in the UV–VIS spectral range and the value of the optical energy gap is determined. The effect of photo-irradiation on the optical absorption and transmission of thin film samples is also investigated. The optical energy gap was found to decrease with photo-irradiation time. The results of photo-irradiation are discussed in correlation with the structural aspects of As₂Se₃. A model is proposed to account for the structural changes, resulting from photo-irradiation, causing the decrease of the energy gap. The effect of γ-radiation on the optical absorption of As₂Se₃ thin films was studied also and no detectable effect on the value of the optical energy gap was observed.     

Influence of Ge and Ag impurities on the thermal conductivity of semiconducting amorphous As2Se3

The thermal conductivity of amorphous semiconducting As₂Se₃ is studied in the temperature range from 100 to 300°K and the influence of germanium and silver impurities is shown. The mean free path of phonons is determined and the observed change of the thermal conductivity is explained by the change of the velocity of sound in amorphous As₂Se₂ containing germanium.Presented by L. toura at the Meeting on Electronic Structure, Optical and Transport Effects in Amorphous and Liquid Semiconductors, Prague, May 1965.The authors are indebted to Dr. J. urek and Ing. I. Turek from the Department of Technical Physics of the College of Transport Engineering in ilina for measuring the velocity of sound in the investigated materials and to Mrs M. Kaparová and J. Trepeová for their help in the experimental work.     

Kinetics of photo‐darkening and self‐bleaching in amorphous As2S3 and As2Se3 thin films

The kinetics of photo‐darkening of amorphous As₂S₃ and a‐As₂Se₃ thin films follows a single exponential, but the magnitude and the rate of the process is higher in case of As₂S₃. The kinetics of self‐bleaching (dark relaxation) in advance photo‐darkened state follows a stretched exponential (SRE) with different stretching parameter for a‐As₂S₃ and a‐As₂Se₃. Within the J. C. Phillips approach we suppose that photo‐darkening in amorphous As₂S₃ films is, to some extent, accompanied by changes in short‐range order interactions, while photo‐darkening of amorphous As₂Se₃ is accompanied rather by changes in Coulomb interactions. The self‐bleaching process reduced the magnitude of photo‐darkening up to 45% and 60% for amorphous As₂S₃ and As₂Se₃ films, respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photo-induced dynamical changes in amorphous As2S3 films

Optical properties of amorphous As₂S₃ films, which have been illuminated well by bandgap light in advance, can be changed dynamically by exposing to less-bandgap light. This dynamical change has been studied in connection with its plausible relation to the reversible photo-induced change. It has been found that these changes have intimate connections with each other, and can be explained by a certain configurational diagram in a coherent fashion.     

Quantum efficiency of light-induced defect creation in hydrogenated amorphous silicon and amorphous As2Se3

The quantum efficiency (QE) of light-induced metastable defect creation in hydrogenated amorphous silicon (a-Si?:?H) and amorphous As₂Se₃ (a-As₂Se₃) by bandgap and subgap illumination has been deduced from photocurrent measurements. The QE decreases with increasing number of absorbed photons. A higher QE for a-As₂Se₃ than for a-Si?:?H has been observed and this is interpreted in terms of the higher structural flexibility of a-As₂Se₃. We have also found that, for both materials, subgap illumination yields a higher QE than does bandgap illumination.     

Effect of in addition on some physical properties of the As2Se3 amorphous system

The effect of In content on do electrical conductivity and DTA of the system (As₂Se₃)_1-x. In_x, x=0, 0.01, 0.05, has been studied. The electrical energy gap was found to increase for an In content 0.01% and decrease for an In content 0.05%. The samples exhibit the three conduction mechanisms proposed by Mott and Davis. The activation energy was calculated for each mechanism. The effect of heating rate on the transition temperatures (T _g,T _c,T _m) was studied and the variation of the crystallization-peak position was used to calculate the activation energy and the order of the crystallization process.     

Photoplasticity of As2Se3 films investigated with combined nanoindentation and AFM methods

Thin As₂Se₃ amorphous chalcogenide films have been studied by nanoindentation and atomic force microscopy in darkness and under illumination by band-gap light. The combination of these two methods has been used to study the peculiarities of the photoplastic effect in amorphous semiconductors. It has been shown by multiple loading indentation experiments that a non-linear mechanism of the formation of the strain response is realized in the As₂Se₃ films subjected to the combined action of light and external mechanical loading. We have observed that light illumination alters the internal friction of the films and their shear modulus. These observations have been considered in the frame of the two-phase model of chalcogenide glasses. Some arguments in favor that the self-organization processes take place in the structure of irradiated film are given.     

Frequency dependent conductivity in As2Se3 and As2Se3 + 15% Sb

Dc and ac measurements were performed on bulk samples of undoped and 15% Sb doped As₂Se₃ as a function of temperature (90–400 K) and frequency (10³–10⁶ Hz). The dc results show an activated conductivity dependence on temperature with an activation energy of 0.8 eV above room temperature. The ac results give a temperature dependent frequency exponent s. The temperature dependence of G _ac is discussed in terms of the mechanisms involved. Results are compared with the predictions of the Quantum Mechanical Tunnelling and Correlated Barrier Hopping models. It is found that doping increases the dc conductivity but has no effect on the ac conductivity.     

Multiphonon absorption in As2S3As2Se3 glasses

Multiphonon absorption in As₂S₃ and As₂Se₃ glasses is well explained by a molecular model in terms of combination bands of high frequency vibrational modes of pyramidal AsY₃ and bent AsYAs groups (Y = SorSe). Multiphonon absorption coefficients in mixed As₂S₃As₂Se₃ glasses are nearly additive in terms of the pure components, suggesting a high degree of non-random mixing.     

On the relationship between thermally stimulated depolarization (TSD) and conductivity of amorphous As2Se3

The TSD peak of amorphous As₂Se₃ is shown not to be simply related to dark conductivity. Some reasons are given to search for a relation between the TSD and a group of localized acceptor-like states having energy 0·84 eV in the band gap. It is possible, that these states act as recombination centres of photoluminescence, which method also points to localized states nearly in the middle of the gap.     

Influence of oblique incidence anisotropy on domain structures in GdCo3 sputtered amorphous films

Domain structures in thin obliquely sputtered amorphous GdCo₃ films here been studied by means of the polar Kerr effect and Bitter technique. The influence of induced anisotropy by oblique deposition on domain arrangement is shown and discussed. Discrete stripe domains different from those observed in Permalloy (weak stripes or stripes type I) have been found and a model of this structure proposed.     

Photoinduced phenomena in mAs2S3·nAs2Se3 amorphous films and their application in micro-optics technology

Photoinduced phenomena, such as photodarkening, photorefraction, and photodissolution, were studied in different compositions of three-component mAs₂S₃·nAs₂Se₃ amorphous films. The main emphasis was on the effect of photoinduced change of dissolution rate since this effect is the basis of many applications of amorphous chalcogenide films. The results of the investigation were compared with photoinduced effects in binary As₂S₃ and As₂Se₃ films. Advanced micro-optical devices: micro-lens and micro-mirror arrays, diffractive gratings, and photonic bandgap crystals, based on three-component amorphous films which possessed optimal photodissolution characteristics were developed. The primary parameters of the micro-optical devices developed are discussed.     

Strong Bragg gratings photoinduced by 633-nm illumination in evaporated As2Se3 thin films

Bragg gratings are used in several photonic devices to reflect, and thus to isolate, specific wavelengths of light. Gratings can be photoinduced in chalcogenide glasses by illumination of bandgap light in an interference pattern. We used holographic interferometry to create Bragg gratings in amorphous As2Se3 thin films with a period of 0.56 microm by illumination with 633-nm light. The quality of the gratings was tested in real time, and refractive-index modulations as high as 0.037 were measured. These gratings were found to be stable over a period of several months if they were kept in the dark.     

Influence of Se atoms on the properties of amorphous Ge

Electron spin resonance (ESR), electrical and optical measurements have been made for Ge_1?xSe_x (0?x?0.35) films in order to elucidate relations between tetrahedrally bonded amorphous semiconductors and chalcogenide amorphous semiconductors. The ESR signal due to dangling bonds in amorphous Ge decreases by increasing Se content. For more than about 20 at. % Se, the electrical conductivity is the activation type and the optical gap increases with the increase of Se content. The model of charged dangling bonds by Street and Mott seems to explain the experimental results.     

Edge assisted epitaxy of CsPbBr3 nanoplates on Bi2O2Se nanosheets for enhanced photoresponse

Bi$_{2}$O$_{2}$Se has been proved to be a promising candidate for electronic and optoelectronic devices due to their unique physical properties. However, it is still a great challenge to construct the heterostructures with direct epitaxy of hetero semiconductor materials on Bi$_{2}$O$_{2}$Se nanosheets. Here, a two-step chemical vapor deposition (CVD) route was used to directly grow the CsPbBr$_{3}$ nanoplate-Bi$_{2}$O$_{2}$Se nanosheet heterostructures. The CsPbBr$_{3}$ nanoplates were selectively grown on the Bi$_{2}$O$_{2}$Se nanosheet along the edges, where the dangling bonds provide the nucleation sites. The epitaxial relationships between CsPbBr$_{3}$ and Bi$_{2}$O$_{2}$Se were determined as ${[200]}_{\rm Bi_{2}O_{2}Se}||{[110]}_{\rm CsPbBr_{3}}$ and ${[110]}_{\rm Bi_{2}O_{2}Se}||{[200]}_{\rm CsPbBr_{3}}$ by transmission electron microscopy characterization. The photoluminescence (PL) results reveal that the formation of heterostructures results in the remarkable PL quenching due to the type-I band arrangement at CsPbBr$_{3}$/Bi$_{2}$O$_{2}$Se interface, which was confirmed by ultraviolet photoelectron spectroscopy (UPS) and Kelvin probe measurements, and makes the photogenerated carriers transfer from CsPbBr$_{3}$ to Bi$_{2}$O$_{2}$Se. Importantly, the photodetectors based on the heterostructures exhibit a 4-time increase in the responsivity compared to those based on the pristine Bi$_{2}$O$_{2}$Se sheets, and the fast rise and decay time in microsecond. These results indicate that the direct epitaxy of the CsPbBr$_{3}$ plates on the Bi$_{2}$O$_{2}$Se sheet may improve the optoelectronic performance of Bi$_{2}$O$_{2}$Se based devices.     

Selective wet-etching of amorphous/crystallized Ag–As–S and Ag–As–S–Se chalcogenide thin films

The paper is focused on the possibilities of selective wet etching of optically and thermally crystallized/amorphous Ag-doped chalcogenide thin films, namely Ag_x(As_0.33S_0.67)_100−x and Ag_x(As_0.33S_0.335Se_0.335)_100−x. The selective etching of optically(thermally) crystallized Ag_x(As_0.33S_0.67)_100−x and thermally crystallized Ag_x(As_0.33S_0.335Se_0.335)_100−x thin films in water solution of NaCN is presented. The good surface quality is an important and crucial parameter for optical elements fabrication (e.g. grids, waveguides, etc.) especially in nanometer dimensions. The selective etching of undoped and Ag optically doped region was also carried out to observe surface roughness of doped region before and after selective etching. Characterization of the structure and surface of studied films by Raman spectroscopy, X-ray diffraction, AFM and SEM methods has been done and potential application suggested.     

Magnetic properties of glassy As2Se3 doped with 3d transition elements

Measurements of magnetic susceptibility, EPR and electrical resistivity of glassy As₂Se₃ doped with Ti, V, Cr, Mn, Fe, Co and Ni are reported. The explanation is based on the assumption that Se atoms are coordinated tetrahedrally around the impurity atom and that the 3d levels are split into two e_g and three 2t_g levels. Results are in a good agreement with this model.It is a pleasure to acknowledge the excellent assistance of Professor F. Kosek, Technical University of Chemical Technology in Pardubice, who prepared the measured samples.