Showing papers in "Journal of Non-crystalline Solids in 1970"
TL;DR: In this paper, the properties and structure of silica glass are discussed, and the following topics are treated: Types of glass, the vitreous state of glass glass, optical properties, absorption and fluorescence, refractive index and homogeneity, mechanical and thermal properties, specific volume, volume relaxation, volume and pressure, elastic and internal friction behaviour, heat capacity and heat conduction, strength, crystallization.
Abstract: This review is concerned with the properties and structure of silica glass. The following topics are treated: Types of silica glasses; The vitreous state of silica glasses: thermodynamical approach, atomistic approach; Optical properties; absorption and fluorescence, refractive index and homogeneity; Mechanical and thermal properties: specific volume, volume relaxation, volume and pressure, elastic and internal friction behaviour, heat capacity and heat conduction, strength, crystallization.
806 citations
TL;DR: The role of cerium and other multivalent ions in suppression of color centers induced by radiation in different borate, silicate and phosphate glasses using optical and ESR techniques is discussed in this paper.
Abstract: This paper discusses, in some detail, the nature of color centers induced by radiation in different borate, silicate and phosphate glasses; using optical and ESR techniques. The role of cerium and other multivalent ions in suppression of some of these centers and in studying their nature is also discussed. In most glasses, the visible induced absorption was associated with positive hole centers. However, at certain compositions, an electron trap center which absorbs in the visible is also induced by radiation, and was associated with certain structural defects, e.g. a non-bridging oxygen ion vacancy neighboring the alkai ions in diborate or disilicate glasses, Pb 2+ ions (or other isoelectronic ions) taking network modifying positions, or Ce 3+ ions in relatively high concentrations. Some examples of the use of radiation induced optical absorption and electron spin resonance as a tool for studying structural changes are also discussed.
306 citations
TL;DR: In this paper, the forming process, by which changes are brought about in the electronic conduction of thin films of various binary amorphous oxides and halides, is described.
Abstract: The forming process, by which changes are brought about in the electronic conduction of thin films of various binary amorphous oxides and halides, is first described, and experimental evidence is put forward which contradicts an earlier theory of the forming process in gold-silicon monoxide-metal structures. A theory is developed, in terms of the growth and thermal rupture of many conducting filaments through the insulating layer, to explain the observed voltage controlled negative resistance, electron emission, electroluminescence and memory phenomena. The model is presented firstly in its simplest phenomenological form, after which some atomic mechanisms which may be involved are tentatively discussed. It is further shown that there is evidence to suggest that the forming process in important in a wide range of systems. These include metal-oxide-silicon capacitors and transistors, surface-barrier junctions on silicon, oxide-coated thermionic cathodes and anodic oxide layers. Electronic conduction in each of these cases is held to take place through localized filamentary paths. The relationship between this and other filamentary conduction models is briefly discussed, and a general classification of negative-resistance devices into regenerative and non-regenerative systems is made.
273 citations
TL;DR: In this paper, the authors used time resolved transient photoconductivity measurements to characterize the transport properties of several vitreous alloys of selenium and found that the predominant effect of isoelectronic additives is the production of mixed rings which decrease the Se8 ring population and, thereby, the electron mobility.
Abstract: Time resolved transient photoconductivity measurements have been used to characterize the transport properties of several vitreous alloys of selenium. Samples were prepared by flash evaporation to insure uniformity of composition. Information derived from infrared and Raman spectroscopy, viscosity, and thermal studies are used to correlate transport effects with atomic structure. In particular, electron transport is associated with Se 8-membered rings. Alloying elements produce characteristic effects depending on whether they are univalent, such as Cl or Tl; isoelectronic with Se, such as S and Te; or capable of producing chain branching, such as As, Bi, or Ge. The latter grouo of additives cause a decrease in electron mobility by reducing the Se8 ring population and produce deep hole traps, presumably at branch points on polymeric chains. However, at higher concentrations, such branch points coalesce and produce a new network with its own characteristic transport parameters. The predominant effect of isoelectronic additives is the production of mixed rings which decrease the Se8 ring population and, thereby, the electron mobility. Tellurium is more effective than sulfur in this respect. The corresponding reduction in hole drift mobility also observed with isoelectronic additives is though to have a different structural origin. Univalent additives produce deep hole or electron traps, even at very low concentrations, which are here associated with coulombic centers.
263 citations
TL;DR: In this article, simple models of the electronic structure of disordered materials are reviewed and the universal features of these models and their consequences for amorphous semiconductors are discussed.
Abstract: The existing simple models of the electronic structure of disordered materials are reviewed. The focus is on the universal features of these models and their consequences for amorphous semiconductors. Simple plausibility arguments are given showing that continuous bands of extended states with tails of localized states associated with fluctuations within the disordered material can always be expected. Models for the mobility in which shoulders occur at the energies of transition from localized to extended states are reviewed. It is a mobility gap rather than a gap in the density of states which is responsible for the activated temperature dependence of the conductivity in amorphous semiconductors. Hopping conduction and the nature of the electronic motion in extended states near the mobility edges is discussed. The latter is likened to Brownian motion within certain limitations. Finally, the Anderson transition is discussed within the present models.
237 citations
TL;DR: In this article, the dc and ac conductivities and thermoelectric power have been measured as a function of the ratio (V 4+ /V total ) in glasses in the system V 2 O 5 -P 2 O5.
Abstract: The dc and ac conductivity and thermoelectric power have been measured as a function of the ratio (V 4+ /V total ) in glasses in the system V 2 O 5 -P 2 O 5 . The conductivity goes through a maximum as the ratio (V 4+ /V total ) is varied but at a much lower value than that expected from a straightforward hopping model (i.e. 0.5) in which all sites contribute equally. The thermoelectric power tends to go through zero but at a different value of (V 4+ /V total ) than the maximum in conductivity. These discrepancies from simple behaviour may be connected with the structural complexity of the glass and at least two suggestions can be made to account for these deviations. The log conductivity versus (1/ T ) plots are not linear and their slopes decrease rapidly at low temperatures. Possible reasons for this behaviour are mentioned. The ac conductivity varies nearly linearly with frequency in the audio- to radio-frequency region and approximately as the square of frequency at higher frequencies. At the same time the high frequency conductivity tends to become independent of temperature. This is almost identical with similar observations in, for instance, chalcogenide glasses.
222 citations
TL;DR: In this article, the optical spectra of some semiconductors (Ge, InSb, Se, Te and As 2 Se 3 ) are reviewed for which the optical properties are known in a broad energy range both in the crystalline and the amorphous phase.
Abstract: The optical spectra are reviewed for some semiconductors (Ge, InSb, Se, Te and As 2 Se 3 ) for which the optical properties are known in a broad energy range both in the crystalline and the amorphous phase. In particular the change of the spectra on the transition to the disordered state is treated and the different behaviour of the semiconductors is discussed. Furthermore recent results on electroreflection are reported. The review of the electrical properties is mainly restricted to conductivity, thermoelectric power and some results on magneto- and piezoresistance. The main features of the intrinsic and the impurity conduction range are pointed out and the influence of impurity atoms and of structure defects are discussed. For the intrinsic conductivity a simple relation is given which is valid for most amorphous semiconductors.
197 citations
TL;DR: In this paper, the theory of plasticity was applied to micrographs and it was shown that glass densification may occur during indentations and simultaneously densification beneath the indentation is a more general property of glasses.
Abstract: Flow of glass may occur during indentations. Remarkable accordance with conclusions from the theory of plasticity was found on micrographs. Simultaneously densification beneath the indentation must be noticed to be a more general property of glasses, whereas flow at room temperature seems to require a minimum percentage of network modifiers.
192 citations
TL;DR: In this paper, a random phase model is used to calculate conductivity, thermopower, and optical absorption of amorphous semiconductors, and an upper limit of 10 17 eV −1 cm −3 can be put on the density of states in the middle of the energy gap, for some bulk semiconducting glasses.
Abstract: A model is studied which assumes that, in the conduting states of an amorphous semiconductor, the phase of the probability amplitude for finding an electron on a particular atomic site varies randomly from atom to atom. This “random phase model” is used to calculate the conductivity, thermopower, and optical absorption. Experimental data on conductivity and thermopower are analyzed for three chalcogenide compositions. There is an upper limit on the mobility of about 20 cm 2 /V sec. The matrix element for an optical transition from conducting states to conducting states is shown to be equal to that from conducting states to localized states. Therefore an upper limit of the order of 10 17 eV −1 cm −3 can be put on the density of states in the middle of the energy gap, for some bulk semiconducting glasses. Measurement of optical absorption of low magnitude in the infrared would make it possible to deduce the density of states as a function of energy in the gap.
152 citations
TL;DR: In this paper, the Mossbauer effect has been used in the study of nuclear gamma ray absorption in crystalline systems, and the theory of the effect and its practical details are presented.
Abstract: Recoil-free emission and resonant absorption of nuclear gamma rays (i.e., the Mossbauer effect) has proven to be an effective tool in the study of certain physical and chemical properties of crystalline systems. The theory of the effect, as well as certain practical details, are presented. On this basis the experimental work on inorganic glasses is discussed and the usefulness of the tool in such systems assessed.
131 citations
TL;DR: In this article, it is suggested that the de-localisation of states in the valence and conduction bands as the short range order increases is due to a hopping process in an impurity band.
Abstract: Films of silicon and germanium are deposited on glass using the radio-frequency glow-discharge decomposition of silane and germane gases respectively. When grown on a substrate at room temperature the films are amorphous, with a short range order of about 20 A. The resistivities of these films, as deposited, are typically 108Ω cm for silicon and 7 × 103 Ω cm for germanium, measured at 294°K. Thermal activation energies for conduction decrease continuously below the deposition temperature, and at low temperatures germanium follows the relation log ’ = A/T 1 4 , where A is a constant. This would seem to indicate that a hopping process in an impurity band is responsible for conduction at low temperatures. Photoconductivity has been observed in silicon but not in germanium. The threshold energy for this effect decreases with increasing deposition or annealing temperatures. This is also true of the high temperature thermal activation energy. It is suggested that this is due to the de-localisation of states in the valence and conduction bands as the short range order increases. The optical absorption coefficients of germanium and silicon have an exponential dependence on photon energy and the considerable absorption below the fundamental absorption edge of the crystalline form may indicate the presence of localised states in the band gap.
TL;DR: In this article, a cinematographic study of filament formation between two point contact probes on the surface of bulk samples of AsTe-Ge was made and electron microprobe analysis and X-ray diffraction were also employed.
Abstract: The Ovshinsky memory effect (electrically reversible bistable resistivity) has been observed in AsTeGe 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 AsTeGe 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 AsTeGe introduced a definite crystallinity. It was not possible, however, to positively identify the crystalline structure.
TL;DR: In this article, the dc and ac conductivity, thermoelectric power, optical absorption and carrier mobility of As2S3, As2Se3 and some other chalcogenide glasses are described and discussed.
Abstract: The dc and ac conductivity, thermoelectric power, optical absorption and carrier mobility of As2S3, As2Se3 and some other chalcogenide glasses are described and discussed. The question of band or hopping conduction is considered and it is concluded that although the ac conductivity involves hopping, the dc properties are best viewed in terms of a band model with a “mobility gap” as introduced by Mott and Cohen. There are, however, some unresolved problems, particularly relating to the ac conductivity.
TL;DR: In this article, the authors calculated the radial distribution of amorphous Ge χ Te 1−χ alloys from X-ray diffraction data for x = 0.11 and 0.54.
Abstract: Radial distribution studies of amorphous Ge χ Te 1−χ alloys have been calculated from X-ray diffraction data for x = 0.11 and 0.54. These show peaks at approximately 2.7 A and 4.2 A. The absence of a peak at the crystalline GeTe first neighbor separation of 3 A is shown to imply that the local coordinations in the amorphous materials are different from those in crystalline GeTe. The areas under the first neighbor peaks indicated that it is very unlikely that the coordination numbers of the Ge and Te atoms are the same. These areas are consistent with models in which the average Ge and Te coordinations are four and two, respectively. This implies that the similarity in the optical absorption edges of crystalline and amorphous GeTe cannot be explained by similarities in short range structures. The similarities in bonding over a wide range of compositions in these amorphous alloys appear to lend support to Mott's picture for the failure of many impurities in many amorphous semiconductors to add significantly to the conductivity. The form of bonding postulated appears to be inconsistent with a microcrystalline picture for these alloys.
TL;DR: In this article, a double-injection space-charge process was proposed to account for the principal features of amorphous threshold switching, and its applicability to chalcogenide glasses under various operating conditions.
Abstract: Description of a double-injection space-charge process which can account for the principal features of amorphous threshold switching, and discussion of its applicability to chalcogenide glasses under various operating conditions.
TL;DR: In this article, a homogeneous 0.08 Rb2O·0.92 SiO2 glass has been tested at temperatures between 480 and 555°C (low-stress viscosities between 1017.1 and 1013.5 poise) and at stress levels up to 109.5 dyne/cm2 or more.
Abstract: A homogeneous 0.08 Rb2O·0.92 SiO2 glass has been tested at temperatures between 480 and 555°C (low-stress viscosities between 1017.1 and 1013.5 poise) and at stress levels up to 109.5 dyne/cm2 or more. At low stress levels, Newtonian behavior was observed; at stress levels above some critical stress, the viscosity was observed to decrease with increasing stress. This critical stress for non-Newtonian flow was found to be about 109.1 dyne/cm2, approximately independent of temperature. The variation of the viscosity with stress in the high-stress region can be described by absolute rate theory only by assuming a flow volume which increases with increasing stress.
TL;DR: In this article, the steady state and transient photoemission of carriers from metal electrodes has been used to study the electronic energy level structure and transport properties of two amorphous insulators, the polymer poly-n-vinyl carbazole (PVK) and ammorphous selenium.
Abstract: Steady state and transient photoemission of carriers from metal electrodes has been used to study the electronic energy level structure and transport properties of two amorphous insulators, the polymer poly-n-vinyl carbazole (PVK) and amorphous selenium. The results for these two materials illustrate different types of information which these combined techniques can give. Fine structure on the steady state spectral response of the photoemission for PVK is identified with vibrational splitting of the valence band which is < 0.1 eV wide. The time resolve transport of holes photoemitted into this band reveals an effective hole mobility which is thermally activated and field dependent, with a value of about 10−7 cm2/V sec at 105 V/ cm and room temperature. For amorphous Se the transient photoemission of holes indicates a transition of the carrier supply from prredominantly internal photogeneration to photoemission. The dependence of the number of transported holes as a function of temperature and applied field shows a change in moving through this transition region. These results are significant with respect to the field dependent photogeneration of carriers in amorphous Se. The observed field dependent supply of photoemitted carriers is attributed to a general metal-insulator interface limitation commonly referred to as an unsaturated blocking contact.
TL;DR: In this article, it is suggested that high field breakdown can be triggered by different processes depending on the temperature and the electrode configuration, and the material characteristics yielding the different switching effects.
Abstract: High field breakdown often leads (i) to a regenerative structural change in the material, or (ii) without any material change, to a conducting state which is maintained only above a certain holding current value. It is suggested that breakdown can be triggered by different processes depending on the temperature and the electrode configuration. The observed high field and non-equilibrium phenomena will be discussed in relation with the several proposed breakdown mechanisms. The material characteristics yielding the different switching effects will be discussed.
TL;DR: In this paper, a model for the dependence of quantum efficiency on photon energy, electric field and temperature is developed, based on the assumptions of a diffusive-like motion of the charge carriers and a relaxation of the k -conservation selection rule for transitions between electronic states.
Abstract: The extent to which the properties of amorphous selenium are in support of the Mott-Cohen model for the electronic states in an amorphous semiconductor is considered. In particular the optical absorption and transport are shown to be consistent with the ideas of mobility edges and localised states. A model for the dependence of quantum efficiency on photon energy, electric field and temperature is developed, based on the assumptions of a diffusive-like motion of the charge carriers and a relaxation of the k - conservation selection rule for transitions between electronic states.
TL;DR: Differential thermal analysis (DTA) and differential calorimeter (DCA) measurements were performed between 300 and 800°K on chalcogenide alloy glasses of various compositions as mentioned in this paper.
Abstract: Differential thermal analysis (DTA) and differential calorimeter (DCA) measurements were performed between 300 and 800°K on chalcogenide alloy glasses of various compositions Fast and slow cooling cycles were used to determine the rates of structure formation After each thermal cycle the electrical conductivity was determined These studies were supplemented by thermal expansion measurements The calorimetric studies distinguish between materials (i) which show no memory effect but only ovonic switching action and (ii) those which show switching effect with memory action The memory materials (ii) show an exothermic reaction at a temperature T1 between 200–300°C and an endothermic reaction at a higher temperature The bistable resistance state of these materials is associated with the formation near T1 The other materials (i) do not show any reaction and remain highly resistive even after slow cooling from the melt
TL;DR: In this paper, the authors review the past work in amorphous switching and discuss some of the operational concepts underlying their continued effort, and describe some of their working hypotheses which pay particular attention to spatial relationships of the localized structural units as a means of developing unusual electronic and electrical changes.
Abstract: This paper will briefly review our past work in amorphous switching and discuss some of the operational concepts underlying our continued effort. In the past, periodicity of atomic structure has been the basis of the understanding of solid state physics. Part of the problem in understanding the amorphous state is the terms themselves, for the words “disordered” and “amorphous” for non-crystalline materials have misleading connotations as they project an image of a material with lack of specific structure. In this paper we will describe some of our working hypotheses which pay particular attention to spatial relationships of the localized structural units as a means of developing unusual electronic and electrical changes in amorphous materials.
TL;DR: Radiative recombination in single crystals and glasses of arsenic sulphide and selenide under photoexcitation was observed in this article, where the recombination was performed in a single crystal and a single glass.
Abstract: Radiative recombination in single crystals and glasses of arsenic sulphide and selenide under photoexcitation is observed
TL;DR: In this paper, the frequency dependence of conductivity at room temperature has been measured for amorphous films of As2Te3, Te2AsSi, and a composition containing Te, As, Si, and Ge.
Abstract: The frequency dependence of conductivity at room temperature has been measured for amorphous films of As2Te3, Te2AsSi, and a composition containing Te, As, Si, and Ge. Results were similar for the three compositions. The conductivity could be considered to consist of two components, a frequency independent component σ0 and a frequency dependent component σ1; the latter varied as ωs with s usually around 0.8 to 0.9. The component σ1 attained a magnitude comparable to σ0 at 105 to 106 Hz, except in the case of point contacts with light contact pressures, where capacitive coupling increased the magnitude of σ1 relative to σ0. The component σ1 is attributed to a hopping mechanism and σ0 is attributed to intrinsic band conduction. Optical data for the fundamental absorption edge is also included.
TL;DR: In this paper, a threefold classification of amorphous semiconductors into (i) elemental, (ii) covalent alloys, and (iii) ionic and tightly bound materials is proposed.
Abstract: A three-fold classification of amorphous semiconductors into (i) elemental, (ii) covalent alloys, and (iii) ionic and tightly bound amorphous materials is proposed. The experimental evidence supporting a simple band model for the amorphous covalent alloys is presented. The present understanding of the reversible switching effects and of the switching with memory is discussed.
TL;DR: In this article, a two-terminal symmetrical voltage sensitive switching device is characterized in terms of both its static and dynamic parameters, and the effect of pre-breakdown bias voltage and polarity reversals on the turn-on mechanism is investigated.
Abstract: The Ovonic Threshold Switch ( ots ), a two-terminal symmetrical voltage sensitive switching device, is a new circuit element, and must be characterized before it can be used in a practical manner by circuit designers. The purpose of this paper is to perform that task. The ots is characterized in terms of both its static and dynamic parameters. A study is made of the blocking state and of the conducting state of the ots . Experiments on switching, both from the blocking to the conductive state and vice versa, are discussed. Also included is a study of energy and charge switching requirements and the effect of pre-breakdown bias voltage and polarity reversals on the turn-on mechanism. The static and dynamic parameters are characterized in terms of temperature, device geometry and other parameters. It is shown that polarity reversals during the pre-breakdown period do not affect delay time and that pre-bias reduces delay time independently of polarity.
TL;DR: In this paper, the steady state and time-dependent photoresponse have been studied in a vacuum-deposited thin film of Ge:Si:As:Te alloy.
Abstract: Steady-state and time-dependent photoresponse have been studied in a vacuum-deposited thin film of Ge:Si:As:Te alloy. In the steady-state at room temperature the quantum efficiency is essentially independent of photon energy, and the photoresponse linear in photon flux. The photoconductive gain factor exhibits a maximum in the neighborhood of 250°K, and decreases exponentially at lower temperatures. At 77°K, the photoresponse varies approximately as the square root of photon flux; while voltage-current curves in the dark and under illumination give evidence of trap-controlled, space-charge-limited conduction. An analysis of the thermally stimulated current following exposure to pair-producing radiation at low temperatures shows that the dominant trapping centers lie approximately in the middle of the mobility gap, and their density probably exceeds 10 19 /cm 3 . An interpretation of these results is offered in terms of the band model of Cohen, Fritzsche and Ovshinsky.
TL;DR: In this paper, the application of a sputtering apparatus suitable for etching as well as for thinning with an ion beam is described, and the limits of application of this method are explained.
Abstract: The application of a sputtering apparatus suitable for etching as well as for thinning with an ion beam is described. Glasses and glass-ceramics can be etched residue-free by ion sputtering. Inhomogeneities in their structure such as segregations and devitrifications are thereby exposed. The preparation of thin specimens for subsequent investigation with transmission electron microscopy is also possible. It is shown, in particular, that with this method thin surface coatings can be cut perpendicularly to the surface for examination by transmission microscopy. During ion bombardment and investigation in the electron microscope, the temperature increase is so insignificant that no defects in the sections could be observed. The limits of application of this method are explained.
TL;DR: A brief review of the CFO model is given in this article, in which its principal features and what may be interpreted as its successes are listed and a few new results lending further support to features of the model are also reviewed.
Abstract: A brief review of the CFO model is given in which its principal features and what may be interpreted as its successes are listed. A few new results lending further support to features of the model are also reviewed. Upper and lower limits are given for the mobilities in the familiar regimes of propagation with occasional scattering and of phonon-assisted hopping between localized states, respectively. Mobilities in disordered materials frequently fall between these limits. Simple physical arguments are given which suggest that carrier motion in this intermediate regime takes place as Brownian motion. An estimate of the upper limit of the mobility for Brownian motion places it about equal to the lower limit for propagation. It is argued that the thermopower of carriers in this intermediate regime should be normal, whereas the Hall coefficient of holes should be negative. A summary of results of Johnson and the author for carrier kinetics in the CFO model is given. A calculation of the I–V characteristics at high field is briefly described.
TL;DR: In this paper, the long wavelength cutoff of chalcogenide glasses is determined by a lattice type absorption, and free carrier absorption is not observed even at elevated temperatures.
Abstract: Glasses based on S, Se, and Te have been under study for a number of years as possible infrared optical materials. Though amorphous in nature, their optical properties are similar to those of crystalline semiconductors. Chalcogenide glasses, as they are called, become transparent on the long wavelength side of an absorption edge while their long wavelength cutoff is determined by a lattice type absorption. In the transparent region, impurity absorption is found. Free carrier absorption is not observed even at elevated temperatures. Other physical properties of chalcogenide glasses related to their use as optical materials, compare favorably with conventional infrared optical materials. Because of their amorphous nature, chalcogenide glasses can be prepared in large, very honogeneous pieces. Optical homogeneity is extremely important when preparing optical components for high resolution optical systems.