Glass Ge Research Articles

Infrared studies of Se-based polynary chalcogenide glasses (III): Y xZ xS xSe 100−3 x (Y = Ge, As; Z = As, Te)

The infrared (IR) absorption spectra for Y x Z x S x Se 100−3 x glasses (Y = Ge, As; Z = As, te), with x = 2.5 and 5.0, are measured in the wavenumber region 700-60 cm −1 at room temperature. These IR spectra are qualitatively explained by comparing with the IR spectra of the binary and ternary glasses. In Ge x As x S x Se 100−3 x glasses ( x ⩽ 5.0), the main spectral features are explained by both spectra of the two ternary glasses Ge x S x Se 100−2 x and As x S x Se 100−2 x . In Ge x S x Te x Se 100−3 x glasses ( x ⩽ 5.0), the main spectral features are well explained by both spectra of the two ternary glasses Ge x S x Se 100−2 x and Ge x Te x Se 100−2 x . On the other hand, main spectral features in As x S x Te x Se 100−3 x glasses ( x ⩽ 5.0) are well explained by both spectra of the ternary glasses As x S x Se 100−2 x and the binary glasses Se 100− x Te x . In these glasses with low concentrations ( x ⩽ 5.0) some chemical bonds are confirmed and some structural units estimated.

A reversible optical transition in SeGe and PSeGe glasses

A reversible optical transition has been found in thin films of SeGe and PSeGe glasses. This optical transition is similar to that found in AsSeGe and AsSeSGe glass films; heating causes the shift of the absorption edge to shorter wavelengths, and illumination moves it to longer wavelengths without crystallization. It was found that the presence of arsenic is not always necessary. Fundamental optical properties of these glasses, i.e. absorption constant, optical energy gap, change of the optical energy gap, and the refractive index by heating and illumination are reported. Change of the optical energy gap and the refractive index is small in SeGe and PSeGe glasses, compared with that in AsSeGe and AsSeSGe glasses.

Optical absorption of glassy semiconductors of the GeSbSe system

The optical transmittance of chalcogenide glasses Ge 2SbSe 7 (I), Ge 3SbSe 6 (II), GeSb 2Se 7 (III) and GeSbSe 3 (IV) was studied in the near infrared spectral region, 0.7–25 μm. The longwavelength tail of the absorption edge can be described by Urbach's rule. At higher absorption levels the absorption coefficient K depends quadratically on the energy of incident radiation. The temperature dependence of the absorption edge is discussed and the optical gaps 1.77 eV (I), 1.67 eV (II), 1.66 eV (III), 1.57 eV (IV) together with the corresponding temperature coefficients are also determined. The studied glasses are quite transparent in the 600–5000 cm −1 wavenumber range.

Photoexpansion and ``thermal contraction'' of amorphous chalcogenide glasses

Expansion due to illumination (photoexpansion) and contraction due to heat treatment (``thermal contraction'') of As–Se–(S)–Ge glass films have been observed utilizing the bimetal structures. This property is related to the reversible photodarkening effect of these chalcogenide glass films.

Kinetics of growth of conductive filament in AsTeGe glasses

Memory (lock-on) phenomena observed in semiconducting glasses of the AsTeGe system have been investigated by electrical, calorimetrical and X-ray methods. Some differences between the memory process observed in high-As glasses and that in low-As glasses have been shown, which include both the waiting time for the process and the growth behaviour of the conductive filament formed between the electrodes. A strong correlation between the waiting time and the crystallization rate has also been indicated for their dependences on both the composition of the glass and the temperature. Finally, the kinetics of growth of the conductive filament during the memory process has been discussed using a simplified model, based on the ionic behaviour of the constituent elements in switch-on plasma, which explains well the polarity dependence of the filament growth.

A reversible optical change in the AsSeGe glass

A novel reversible change in the optical property, transmission and refractive index, due to light irradiation has been found in the AsSeGe glass film. The change is not related with a usual amorphous-crystalline type transformation; a weak lightr causes an edge shift to longer shorter wavelengths also occur upon heating the sample, which suggests that the shift du to the strong light irradiation is originated from the “heating effect” of light. This was confirmed by an experiment with a sample coated with metal-smoke. The change of optical transmission during the weak light irradiation was measured; it is decreased exponentially with time, and the rate of decrease became larger as the power of irradiationg light increased. Good reversibility of the optical transmission was obtained, which makes the material suitable for erasable (optical) memory medium.

Laser-Induced Refractive-Index Change in As–S–Ge Glasses

Effect of light irradiation on evaporated chalcogenide glass films of an As–S–Ge system has been studied. In order to make quantitative measurements of refractive-index change resulting from light irradiation, light diffraction efficiency from the phase grating produced in the films with the technique of holographic storage has been measured. The maximum refractive-index change of 0.056 has been obtained in an As2S3 film. This value is two orders of magnitude higher than that of Fe-doped LiNbO3 single crystals. Light irradiation onto the films is considered to have two competing effects, one being thermal and the other purely optical.

Structural and electrical properties of some TeAsGeS glasses

Electrical and DTA measurements have been performed on TeAsGeS glasses. In this group, As 2Te n Ge (4 ⩽ n ⩽ 7) glasses are of particular interest since, in the AsTeGe vitrigfication diagram, they all are located on a straight line crossing completely one of the two vitrification regions. The comparison of the results of DTA on As 2Te 3, Te 4Ge and As 2Te n Ge (4 ⩽ n ⩽ 7) shows that the structure of the As 2Te n Ge glasses is built around the Ge atoms. The electrical properties of a particular family whose composition is near As 2Te 5Ge + S as vitrificant agent are given. Photoelectron spectroscopy has also been used for an investigation of the structure of this last family and permits to conclude that in the crystallized state, phase separations occur.

Vaporization associated with surface electrical switching in semiconducting AsTeI and AsTeGe glasses

Vapor species resulting from electrically-induced threshold switching and memory filament formation on the surfaces of bulk AsTeI and AsTeGe glasses are identified. The common parent species are As 4 (most intense) and Te 2. The results emphasize the importance of thermal mechanisms, and yield information concerning the kinetics of filament formation.

Compositions and Structures of the ``Lock-on'' Filaments in As–Te–Ge Glasses

Compositions and Structures of the ``Lock-on'' Filaments in As–Te–Ge Glasses

Atomic distribution in the glass forming system GeAsSe

The atomic distribution curves of chalcogenide glasses with the compositions 1, Ge 30Se 70; 2, Ge 20Se 40As 40; 3, Ge 35Se 25As 40; and 4, Ge 45Se 25As 30 have been determined. The coordination numbers obtained for the first coordination sphere correspond to the weighted mean of Ge coordination number 4, As 3, and Se 2. Also the distance between nearest neighbours corresponds to the average of the calculatable covalent distances. The glass Ge 30Se 70 shows an atomic distribution which is similar but with larger distances to that expected for a smeared out GeS 2 lattice.

Electron microprobe analysis and radiometric microscopy of electric field induced filament formation on the surface of AsTeGe glass

The reversible formation and growth of filaments between two electrodes placed on the surface of a chalcogenide glass is described. The composition of the filament and the surface temperature during the filament formation were measured.

Electric field-induced filament formation in AsTeGe glass

The Ovshinsky memory effect (electrically reversible bistable resistivity) has been observed in AsTeGe glass (55%-35%-10% respectively by atomic percent). It is generally thought that an electrically induced conducting filament is responsible for the low resistance state. A cinematographic study of filament formation between two point contact probes on the surface of bulk samples of AsTeGe was made. To further characterize these filaments, electron microprobe analysis and X-ray diffraction were also employed. The cinematography results showed that the filament always grew out of the positive voltage terminal and that the formation of a continuous filament coincided with the establishment of a stable low resistance state. The electron microprobe analysis indicated that inside the filament there was a 37.6% (weight percent) increase in Te, a 40.8% decrease in As and a 47% decrease in Ge compared to the composition some distance away from the filament. X-ray diffraction patterns showed that the electric field-induced formation of filaments on the surface of amorphous AsTeGe introduced a definite crystallinity. It was not possible, however, to positively identify the crystalline structure.

Electrical Conductivity and Formation of Chalcogenide Glasses in Ge–As–Se and Ge–Sb–Se Melts

Electrical Conductivity and Formation of Chalcogenide Glasses in Ge–As–Se and Ge–Sb–Se Melts