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Journal ArticleDOI

Quenching Effects and Negative Photoconductivity in Amorphous Selenium

01 Nov 1961-Journal of Chemical Physics (American Institute of Physics)-Vol. 35, Iss: 5, pp 1628-1635
TL;DR: In this paper, negative photoconductivity and long wavelength quenching were observed in several evaporated layers of amorphous Se, with both effects showing a maximum for light energy between 1.9 and 2.1 ev.
Abstract: Negative photoconductivity and long wavelength quenching of photoconductivity have been observed in several evaporated layers of amorphous Se, with both effects showing a maximum for light of energy between 1.9 and 2.1 ev. From the position of the Fermi level, these effects have been identified with transitions from a set of sensitizing centers ranging from less than 0.58 to 0.65 ev above the valence band. Deep traps were investigated by thermally stimulated currents and by the analysis of space charge limited currents. Trapping states at 0.55 ev were detected which probably correspond to the same set of defect levels as the sensitizing centers. Several models which might account for the optical absorption, spectral response, quenching phenomena, and the exponential temperature dependence of the carrier mobilities, are discussed.
Citations
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Journal ArticleDOI
TL;DR: In this paper, the effect of highly absorbed light in increasing the growth rate of surface crystallites in vitreous (amorphous, polymeric) selenium films has been studied in detail.

139 citations

Journal ArticleDOI
TL;DR: In this article, a model is proposed to explain the outstanding features of the free-carrier photogeneration process in amorphous selenium, where the excitation of an electron-hole pair and the subsequent separation or recombination are considered as a function of photon energy, applied electric field and temperature.

131 citations

Journal ArticleDOI
01 Aug 1962
TL;DR: In this paper, the basic principles of one and two-carrier, volume-controlled injection currents are reviewed and the concepts of shallow and deep traps are defined and their effects on injected currents studied.
Abstract: The basic principles of one- and two-carrier, volume-controlled injection currents are reviewed. One-carrier injected currents are necessarily space-charge-limited and are strongly affected by the presence of traps which usually capture and immobilize most of the injected carriers. The trapped carriers are in an effective thermal equilibrium with the free injected carriers. The concepts of "shallow" and "deep" traps are defined and their effects on injected currents studied. It is shown that the presence of "deep" traps leads to a very steep rise of current with voltage, resembling a breakdown curve, at an appropriate voltage. Under double injection, that is, the simultaneous injection into the insulator of electrons from a cathode and holes from an anode, space-charge limitations are at least partially overcome but recombination of injected carriers presents a new limitation on the current flow. In any insulator at sufficiently high injection levels both recombination and space charge contribute to limitation of the current, leading to a dependence of current on the cube of the voltage, for monomolecular recombination processes. For double injection into a semiconductor, the presence of thermally generated free carriers leads to charge neutrality (the so-called ohmic relaxation process) and recombination alone limits the current. In a semiconductor long compared to a diffusion length this leads to a dependence of current on the square of the voltage.

90 citations

Journal ArticleDOI
TL;DR: In this article, D.A.H.B. and J.-L.L. contributed equally to this work and acknowledged the KAUST competitive research grant (CRG7, No. 3737) for financial support.
Abstract: M.A.H. and J.-L.L. contributed equally to this work. Research reported in this publication was supported by the King Abdullah University of Science and Technology (KAUST). D.B. acknowledges the KAUST competitive research grant (CRG7, No. 3737) for financial support. The work at CSRC was supported by the National Key Research and Development Program of China under Grant No. 2016YFB0700700, the National Nature Science Foundation of China under Grant Nos. 51672023, 11634003, and U1530401; and the Science Challenge Project under Grant No. TZ20160003.

35 citations

References
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Book
01 Jan 1978

1,693 citations

Journal ArticleDOI
Albert Rose1
TL;DR: The presence of traps not only reduces the magnitude of space-charge-limited currents, but also is likely to distort the shape of the currentvoltage curve from an ideal square law to a much higher power dependence on voltage.
Abstract: Currents, far in excess of ohmic currents, can be drawn through thin, relatively perfect insulating crystals. These currents are the direct analog of space-charge-limited currents in a vacuum diode. In actual crystals, the space-charge-limited currents are less than their theoretical value for an ideal crystal by the ratio of free to trapped carriers. Space-charge-limited currents become, therefore, a simple tool for measuring the imperfections in crystals even in the range of one part in ${10}^{15}$.The presence of traps not only reduces the magnitude of space-charge-limited currents, but also is likely to distort the shape of the current-voltage curve from an ideal square law to a much higher power dependence on voltage. The particular shape can be used to determine the energy distribution of traps.The presence of traps tends to uniformize the charge distribution between electrodes, to introduce a temperature dependence of the current, and to give rise to certain transient effects from which capture cross sections of traps may be computed.Space-charge-limited currents offer another mechanism for electrical breakdown in insulators.

1,526 citations

Journal ArticleDOI
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

Journal ArticleDOI
R. G. Kepler1
TL;DR: The drift mobilities of electrons and holes in anthracene crystals have been measured using a pulsed photoconductivity technique as mentioned in this paper, and the results indicate that the charge carriers are not produced in the interior of the crystal, but that they are released from a surface layer of a crystal either directly by photons or by excitons which migrate to the surface.
Abstract: The drift mobilities of electrons and holes in anthracene crystals have been measured using a pulsed photoconductivity technique. The mobilities found at room temperature vary from about 0.3 ${\mathrm{cm}}^{2}$/volt sec to about 3 ${\mathrm{cm}}^{2}$/volt sec, depending on the crystal orientation, and the mobilities increase as the temperature is lowered. The wavelength dependence of the number of charge carriers produced by a pulse of light, as well as other experimental data, indicates that the charge carriers are not produced in the interior of anthracene crystals, but that they are released from a surface layer of the crystal either directly by photons or by excitons which migrate to the surface.

527 citations