One of the most important parameters which determine the performance of many modern devices based on amorphous semiconductors is the drift mobility-lifetime product,
μτ. There has been much interest ...in determination of charge-carrier ranges in amorphous semiconductors by various measurement techniques. Although the mobility, μ, can be measured by the conventional time-of-flight transient photoconductivity technique, the determination of the lifetime, τ, is often complicated by both experimental and theoretical limitations. The present article provides an overview of xerographic measurements as a tool for studying the electrical properties of amorphous semiconductors. First, details of the experimental set-up are discussed. Thereafter, the analysis and interpretation of dark discharge, the first cycle residual potential, cycled-up saturated residual potential are considered. It is shown that from such measurements the charge-carrier lifetime,
τ, the range of the carriers,
μτ, and the integrated concentration of deep traps in the mobility gap can be readily and accurately determined. Xerographic measurements on Se-rich amorphous photoconductors have indicated the presence of relatively narrow distribution of deep hole traps with integrated density of about 10
13
cm
−
3
. These states are located at ~
0.85
eV from the valence band. A good correlation was observed between residual potential and the hole range, in agreement with the simple Warter expression. The capture radius is estimated to be
r
c
=
2–3
Å. Since
r
c
for pure a-Se and a-As
xSe
1
−
x
is comparable to the Se–Se interatomic bond length in a-Se, it can be suggested that deep hole trapping centers in these chalcogenide semiconductors are neutral-looking defects, possibly of intimate valence-alternation pair (IVAP) in nature. The absence of any electron spin resonance signal (ESR) at room temperature seemed to be a strong argument in favor of this suggestion. Finally, photoinduced effects on xerographic parameters are discussed. It has been shown that photoexcitation of a-As
xSe
1
−
x
amorphous films with band-gap light alters deep hole and electron states. During room-temperature annealing photosensitized states relax to equilibrium. Recovery process becomes slower with increasing As content. Qualitative explanation of the observed behavior may be based on associating the deep states with C
3
+ and C
1
−intimate-valence-alternation–pair (IVAP) centers.
► In this study we examine gap states via xerographic spectroscopy. ► Parameters which are important: dark decay, first and cycled-up residual potentials. ► Time and temperature dependence of these parameters gives the corresponding characteristic of gap states. ► Photoinduced changes of xerographic parameters are considered.
Some novel results of physical aging studies in glassy selenium Pal, Shiv Kumar; Mehta, N.; Mikla, V.I. ...
Materials science & engineering. B, Solid-state materials for advanced technology,
September 2020, 2020-09-00, 20200901, Volume:
259
Journal Article
Peer reviewed
•Observation of nano-structuring in aged samples after 10 years of natural storage.•Signature of aging-induced self-organization in the old sample of glassy Se.•Results are important to increasing ...the durability of devices made Se rich glasses.•Aging phenomenon reflects the straightening/shrinkage effects in Selenium glass.
Physical aging (PhA) of disorder materials is still an important problem in areas of physics, chemistry and materials science for the study even nowadays. This work reports the results of some novel observations during the devitrification of the aged and as-quenched glassy selenium. Investigation of physical aging effect induced by natural storage up to 10 years aged Selenium glass has been carried out using the state of art experimental techniques (DSC, XRD, SEM, TEM and Raman spectroscopy). Further, the thermal stability, micro-hardness, density, fragility index and compactness of the aged and as-quenched glassy selenium have been determined to see the effect of aging on the glassy Se. The results show that there are significant changes in themechanical behavior of g-Se due to physical aging.
This work provides the consequence of aging on the conduction mechanism of fresh as well as aged Se and As
2
Se
3
chalcogenide glasses (ChGs). In this analysis, the sample synthesized by the ...melt-quench route was used as identical disk-shaped pellets for current–voltage (
I
–
V
) characteristics at different temperatures. Our observation shows the absence of space charge limited conduction (SCLC) for both fresh as well as aged samples of Se and As
2
Se
3.
The Poole–Frenkel conduction mechanism is detected as the leading model for fresh and aged samples of both Se and As
2
Se
3
glasses. The activation energy is found to rise appreciably due to the aging effect of Se while almost constant for As
2
Se
3
samples. The reason behind this may be the slight growth of crystallite due to aging in Se glass.
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•The experimental/theoretical understanding of physical aging in chalcogenide glasses has been reviewed.•General symptoms, peculiarities, and characteristics of PhA have been ...discussed.•Investigations of PhA in industrial glass (As2Se3) have been reported.
The time-dependent variation in the physical properties is one of the most interesting and mysterious behaviors of melt-quenched disordered solids (like polymer glasses, metallic glasses, and especially in chalcogenide glasses). This phenomenon is recognized as physical aging which reveals that the as-quenched glass stays in a meta-stable state (i.e., a thermodynamically non-equilibrium state) and so a thermally activated structural relaxation is the general characteristics of each glass as a consequence of natural or artificial physical aging (PhA). This review starts with the general introduction of PhA and its features. Different perceptive and peculiarities of PhA have been discussed keeping in mind the case of long-term PhA and anti-aging effects of arsenic in the chalcogenide glasses (ChGs) of the Se-As system. Further, we have reported the case study of As2Se3 stoichiometric glass and the results of some new observations during the natural aging of the Arsenic Tri-Selenide glass (g-As2Se3). The thorough inspection of PhA effects in this industrial glass is done after storing at ambient temperature in a glovebox for ten years. Thermal analysis is done by using differential scanning calorimetry. The XRD and TEM/SEM techniques have been employed for structural analysis. The information of various kinds of bonding is acquired by using Raman spectroscopy. Also, we have determined the thermal stability parameter, Vickers hardness, compactness, fragility, and density of the fresh and old samples of As2Se3 glass to see the consequences of PhA. Finally, the new advances and present status related to the studies of PhA have been discussed.
Structure and its transformation are examined for amorphous Se-rich AsxSe1-x (0 ≤ x ≤ 0.2) alloys by employment of diffraction and non-diffraction structural probes. It is shown that the molecular ...structure of amorphous Se (a-Se) on the scale of short-range order is close to that of crystalline phase, while medium-range order differs from the structure of most inorganic glasses and may be placed between three-dimensional network glasses and polymeric ones. Further experiments show the existence of successive phases in laser-induced glass-crystalline transition with pronounced threshold behavior. Below the energy density threshold, Eth, only small changes in the local structure of the system can be detected. Above Eth, the changes were attributed to crystallization transformation. The corresponding Raman spectra reveal transformation of the system from amorphous into the crystalline phase under laser irradiation. In the binary AsxSe1-x glass system, a change of structural regime takes place near the composition x ≈ 0.04. The presence of this topological threshold is established by direct and indirect evidence, such as peculiarities in the composition dependence of the basic parameters for electron diffraction and Raman vibration modes. The peculiarities are caused by the transition from a chain-ring-like structure to preferentially a chain-like structure. Experiments described in this section have shown that Raman technique is a particularly sensitive method to determine the presence of microcrystal's in the glassy matrix. Room-temperature polarized Raman scattering spectra of model glass have been collected. Low-frequency peaks were observed in the spectra. A model is proposed for explanation of their appearance. It is shown clearly that the low-frequency Raman spectra allow determining the conditions at the boundaries, sizes as well as concentration of micro-heterogeneities in non-crystalline materials. It was established earlier that for all amorphous (glassy) materials a low-frequency peak, observed in the corresponding spectral region of Raman scattering and called boson peak, is inherent. This peak is absent in crystals of the same chemical composition and is associated with space correlations on the scale of medium-range order Rc ≈ 10 Å. On the contrary, less known is that a boson peak can give important information about the presence of microcrystalline inclusions and heterogeneities in the low-frequency Raman spectra of glasses irrespective to their chemical composition.
Informative and relatively simple spectroscopic technique, namely thermally stimulated depolarization currents, is considered for studying of defect states in the mobility gap of amorphous Se-based ...semiconductors.
This book presents experimental results on the structural and electronic metastable states in Se-rich chalcogenides. Coverage includes states in the mobility gap, structural transformation, ...photocrystallization, and many potential related applications.
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