Space-charge-limited currents and electron traps in cds crystals
TL;DR: In this article, the authors measured thermally stimulated currents after the electrical injection of electrons in thin insulating crystals of cadmium sulphide which can support large space-charge-limited currents.
Abstract: Thermally stimulated currents have been measured after the electrical injection of electrons in thin insulating crystals of cadmium sulphide which can support large space-charge-limited currents. Two trapping levels which lie 0.41 ev and 0.61 ev below the conduction band are filled with electrons when currents in the vicinity of the traps-filled limit are passed. When currents which lie within the region of Child's Law for solids are allowed to flow the concentration of trapping levels at 0.61 ev decreases while the number of levels at 0.41 ev increases. Measurements of the dark current in the ohmic region suggest that the 0.41 ev trapping complex is stable at temperatures below 0°C and is converted to a complex with a level at 0.61 ev at higher temperatures.
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TL;DR: In this paper, the effects of moderate electric fields (≤3×103 V/cm) on the trapping processes in photosensitive CdS-CdSe single crystals have been investigated using photoelectronic techniques.
Abstract: The effects of moderate electric fields (≤3×103 V/cm) on the trapping processes in photosensitive CdS‐CdSe single crystals have been investigated using photoelectronic techniques Possible mechanisms such as injection of electrons, extraction of holes, dielectric polarization due to inhomogeneities, Joule heating, electrochemical effects, impact ionization, field‐assisted tunneling, and field‐associated changes in the capture cross sections and/or thermal emission probabilities of traps are considered Evidence is presented for the reality of field‐associated changes in trapping parameters in the absence of all the other possible effects Results are consistent with a field emptying of Coulomb‐attractive traps by a decrease in the trap depth and a decrease in the capture cross section of traps The conclusions may be relevant to the interpretation of space‐charge‐limited current data and to mechanisms capable of leading to improved photoconductor speed for low intensity excitation
47 citations
TL;DR: In this article, the CdS dispersion mediated photoinduccd dimerization of N-vinyl carbazole (NVC) has been investigated and found to be efficient.
32 citations
TL;DR: In this article, measurements of space-charge-limited currents have been performed on CdSe single crystals between 77 and 400 °K and four groups of electron trapping levels have been found at 0.64, 0.49, 0.35 and 0.167 eV, with densities ranging from 5 × 1010 to 1013 cm−3.
Abstract: Measurements of space‐charge‐limited currents have been performed on CdSe single crystals between 77 and 400 °K. Four groups of electron trapping levels have been found at 0.64, 0.49, 0.35, and 0.167 eV, with densities ranging from 5 × 1010 to 1013 cm−3. A check of the results with photocurrent vs light intensity and thermally stimulated currents measurements is presented. The origin and the nature of these centers is discussed and correlated with mobility values measured in the crystals investigated. Finally, contacts and geometry considerations are reported.
28 citations
TL;DR: In this article, the luminescence of CdS and mixed ZnS ·CdS semiconductor particles supported in Nafion polymer films has been studied to elucidate the previously reported synergism in the ZnsS · Cds system for photoredox H2 production.
20 citations
TL;DR: In this paper, it was shown that the thermally stimulated current spectrum is critically dependent on the optical stimulation and thermal emptying procedures, and that it may not always be necessary to explain the appearance and disappearance of traps by other more complicated models, for example photosynthesis.
Abstract: Difficulties experienced in obtaining reproducible results from thermally stimulated current analysis have led to a reconsideration of the basic mechanisms involved, and it is shown that the thermally stimulated current spectrum is critically dependent on the optical stimulation and thermal emptying procedures. It may not always be necessary to explain the appearance and disappearance of traps by other more complicated models, for example photosynthesis. A brief survey is made of other factors giving deviations from the basic mechanism.
19 citations
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Abstract: An ohmic contact between a metal and an insulator facilitates the injection of electrons into the insulator. Subsequent flow of the electrons is space-charge limited. In real insulators the trapping of electrons in localized states in the forbidden gap profoundly influences the current flow. The interesting features of the current density-voltage ($J\ensuremath{-}V$) characteristic are confined within a "triangle" in the $logJ\ensuremath{-}logV$ plane bounded by three limiting curves: Ohm's law, Child's law for solids ($J\ensuremath{\propto}{V}^{2}$) and a traps-filled-limit curve which has a voltage threshold and an enormously steep current rise. Simple inequalities relating the true field at the anode to the ohmic field facilitate qualitative discussion of the $J\ensuremath{-}V$ characteristic. Exact solutions have been obtained for an insulator with a single, discrete trap level in a simplified theory which idealizes the ohmic contact and neglects the diffusive contribution to the current. The discrete trap level produces the same type of nonlinearity discovered by Smith and Rose and attributed by them to traps distributed in energy.
1,079 citations
TL;DR: In this paper, it was shown that six major sets of electron traps can be found in cadmium sulphide crystals prepared in this laboratory, with depths of 0.41, 0.83 and 0.63 eV.
Abstract: Conductivity glow curve experiments have shown that six major sets of electron traps can be found in cadmium sulphide crystals prepared in this laboratory. Traps which lie 0.25 eV below the conduction band are associated with excess cadmium. These centres disappear when a crystal is irradiated with white light at or near room temperature, while two new traps appear with depths of 0.41 and 0.83 eV. The process is reversible, and the initial 0.25 eV levels can be restored by heating at 100°C in the dark. The 0.25 eV trap is not found in sulphur-rich crystals. Experiments on sulphur-rich samples as grown, indicate the presence of traps lying 0.41, 0.83 and 0.63 eV below the conduction band. Heat treatment at 100°C removes all trace of these three centres from a subsequent glow curve. The 0.41 and 0.83 eV centres can be produced by illuminating a crystal which is maintained at a temperature between -50 and +20°C. The 0.63 eV trap only is created when the crystal is held at +80°C during the irradiation. A tentative explanation of these effects is given in terms of associated defects.
68 citations
01 Jan 1963
TL;DR: In this paper, a three-level model was proposed for cadmium sulphide consisting of high and nearly equal densities of shallow donor levels and deep trapping levels and a moderately shallow trapping level with a density of about 1017/cm3 at a depth of about 0.40 ev below the conduction levels.
Abstract: Injected space charge trapped in the space-charge-limited dielectric diode by cooling under forward voltage bias is thermally released on warming under reverse voltage bias. Measurements on cadmium sulphide diodes are presented. The temperature dependence of reverse current shows narrow peaks produced by the thermal emptying of trapping levels. A three-level model is proposed for cadmium sulphide consisting of high and nearly equal densities of shallow donor levels and deep trapping levels and a moderately shallow trapping level with a density of about 1017/cm3 at a depth of about 0.40 ev below the conduction levels.
31 citations
01 Jun 1963
TL;DR: In this paper, it was shown that the trap-filled theory of one carrier space-charge-limited currents can be applied to cadmium sulphide, but it is necessary to ensure that the electrical contacts to the crystals exclude the possibility of minority carriers entering the crystal.
Abstract: In order to test whether Lampert's theory (1956) of one carrier space-charge-limited currents can be applied to cadmium sulphide it is necessary to ensure that the electrical contacts to the crystals exclude the possibility of minority carriers entering the crystal. The use of many materials, including indium, can lead to hole injection at the anode at sufficiently high voltages. However, evaporated indium forms good electron injecting cathodes and hole blocking anodes, when it is deposited on surfaces previously subject to hydrogen ion bombardment. With these contacts current-voltage characteristics were measured over a range from -183 °c to 83 °c. Analysis of the results shows that a typical crystal contained 2.5 × 1014 traps per cm3 at a distance of 0.61 eV below the conduction band. About 1012 cm-3 of these were filled with electrons which originated from shallow donors. According to Lampert's traps-filled theory the crystal contained 2.5 × 1013 traps per cm3. It is concluded that the steep rise in current, attributed in Lampert's theory to the complete filling of traps, is in fact associated with trap emptying in this crystal.
27 citations