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Theory of transient space-charge perturbed currents in insulators
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ABSTRACTS OF PAPERS TO APPEAR IN J. PHYS. CHEM. SOLIDS
have a chance to recombine. A study of light intensity vs. electric field suggests an avalanche breakdown characterized by an ionization constant for holes which depends exponentially on the Inverse electric field. These p ii p structures are prepared by zinc diffusion into manganese doped (p-type) GaAs, and a mechanism is suggested for the formation of the high resistivity layer. The current-voltage characteristics before breakdown are essentially ohmic up to several volts suggesting the absence of space charge limitation for the current in such thin layers. -
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(Received 25 July 1966) (Revised 13 September 1966) 5.
6.
SPECTRAL SENSITIZATION OF ZnO THIN FILMS WITH ORGANIC DYES S. J. Dudkowski, A. G. Kepka and L. I. Grossweiner (Department of Physics, Illinois Institute of Technology, Chicago, Illinois, U. S. A.)
Photoconductive couples in which a ZnO thin film is placed in surface contact with a layer of aggregated organic dye have been Investigated under low-intensity illumination and with flash lamp methods. For the dyes studied (crystal violet, mèthylene blue, eosln-Y, and acridlne orange) it was found that the photoresponse at visible wavelengths varies with the squareroot of the incident light intensity, linearly with the dark current, and builds-up and decays via exponential processes. Measurements made during the formation of the couples show that ZnO conduction electrons are transferred to the dye in the dark and return when the dye layer is illuminated. A Schottky barrier model is proposed, in which ZnO conduction electrons are trapped in interfacial levels close in energy to the dye ground state. The theory Indicates that the fraction of ZnO conduction electrons (~ n/n0) transferred in the dark is approximately related to the ZnO thermoelectric work (cp) and the dye photoelectric work function (~) by: ~ ~P+ A (t~n/n0) ~, where A is a constant determined by ZnO parameters. The data for the different dyes studied are in reasonable agreement with this result. A detailed analysis of the model leads to predictions of the kinetic processes in agreement with experiment, (Received 12 August 1966) (Revised 13 September 1966)
Vol.4, No.10
THE MAGNETOACOUSTIC EFFECT IN THALLIUM Julian B. Coon, Claude G. Grenier and Joseph M. Reynolds (Department of Physics Louisiana State University, Baton Rouge, Louisiana),
Geometric resonances in high purity thallium metal have been observed with longitudinal sound waves propagated along the three major axes at frequencies up to 162 Mc. The calipers of both sections of the third band hole surface and those assigned to the fourth band electron surfaces are in general agreement with the band calculation of Soven, even though some data associated with the fourth band appears to agree ‘i.~ellwith the nearly-free electron theory. Evidence of open orbits in the [1010] direction has been seen which is in agreement with the predicted degeneracy of the third and fourth bands along AL. No open orbits were seen in the [0001 J direction establishing further evidence for the non-connectivity of the fourth band electron surface in the c-direction. (Received 25 May 1966) (Revised 29 August 1966) 7.
THEORY OF TRANSIENT SPACE-CHARGE PERTURBED CURRENTS IN INSULATORS A. C. Papadakis (Post Office Research Station, Dollis Hill, London N. W. 2)
The problem of space charge perturbed (SCP) currents resulting from the drift of excess carriers in insulators is considered. Assuming the excess carriers to be instantaneously produced in a narrow sheet close to or~of the electrodes expressions for the resulting SCP currents and the carrier transit times are derived. Secondary injection currents are excluded by means of blocking contacts and carrier capture at both shallow and deep trapping centres during transit Is allowed. It Is shown that the field perturbations due to the space-charge of the excess carriers cause the initially narrow carrier sheet to broaden, even in the absence of diffusion. The time dependence of the resulting current pulse is found to be strongly dependent on the ration of the applied field to the field due to the excess carriers. The results of the present theory are compared to those for the transient space-charge limited currents obtained by Many and Rakavy (~ys. Rev. 126, 1980 (1962). (Received 20 July 1966)
ABSTRACTS OF PAPERS TO APPEAR IN J. PHYS. CHEM. SOLIDS
have a chance to recombine. A study of light intensity vs. electric field suggests an avalanche breakdown characterized by an ionization constant for holes which depends exponentially on the Inverse electric field. These p ii p structures are prepared by zinc diffusion into manganese doped (p-type) GaAs, and a mechanism is suggested for the formation of the high resistivity layer. The current-voltage characteristics before breakdown are essentially ohmic up to several volts suggesting the absence of space charge limitation for the current in such thin layers. -
-
(Received 25 July 1966) (Revised 13 September 1966) 5.
6.
SPECTRAL SENSITIZATION OF ZnO THIN FILMS WITH ORGANIC DYES S. J. Dudkowski, A. G. Kepka and L. I. Grossweiner (Department of Physics, Illinois Institute of Technology, Chicago, Illinois, U. S. A.)
Photoconductive couples in which a ZnO thin film is placed in surface contact with a layer of aggregated organic dye have been Investigated under low-intensity illumination and with flash lamp methods. For the dyes studied (crystal violet, mèthylene blue, eosln-Y, and acridlne orange) it was found that the photoresponse at visible wavelengths varies with the squareroot of the incident light intensity, linearly with the dark current, and builds-up and decays via exponential processes. Measurements made during the formation of the couples show that ZnO conduction electrons are transferred to the dye in the dark and return when the dye layer is illuminated. A Schottky barrier model is proposed, in which ZnO conduction electrons are trapped in interfacial levels close in energy to the dye ground state. The theory Indicates that the fraction of ZnO conduction electrons (~ n/n0) transferred in the dark is approximately related to the ZnO thermoelectric work (cp) and the dye photoelectric work function (~) by: ~ ~P+ A (t~n/n0) ~, where A is a constant determined by ZnO parameters. The data for the different dyes studied are in reasonable agreement with this result. A detailed analysis of the model leads to predictions of the kinetic processes in agreement with experiment, (Received 12 August 1966) (Revised 13 September 1966)
Vol.4, No.10
THE MAGNETOACOUSTIC EFFECT IN THALLIUM Julian B. Coon, Claude G. Grenier and Joseph M. Reynolds (Department of Physics Louisiana State University, Baton Rouge, Louisiana),
Geometric resonances in high purity thallium metal have been observed with longitudinal sound waves propagated along the three major axes at frequencies up to 162 Mc. The calipers of both sections of the third band hole surface and those assigned to the fourth band electron surfaces are in general agreement with the band calculation of Soven, even though some data associated with the fourth band appears to agree ‘i.~ellwith the nearly-free electron theory. Evidence of open orbits in the [1010] direction has been seen which is in agreement with the predicted degeneracy of the third and fourth bands along AL. No open orbits were seen in the [0001 J direction establishing further evidence for the non-connectivity of the fourth band electron surface in the c-direction. (Received 25 May 1966) (Revised 29 August 1966) 7.
THEORY OF TRANSIENT SPACE-CHARGE PERTURBED CURRENTS IN INSULATORS A. C. Papadakis (Post Office Research Station, Dollis Hill, London N. W. 2)
The problem of space charge perturbed (SCP) currents resulting from the drift of excess carriers in insulators is considered. Assuming the excess carriers to be instantaneously produced in a narrow sheet close to or~of the electrodes expressions for the resulting SCP currents and the carrier transit times are derived. Secondary injection currents are excluded by means of blocking contacts and carrier capture at both shallow and deep trapping centres during transit Is allowed. It Is shown that the field perturbations due to the space-charge of the excess carriers cause the initially narrow carrier sheet to broaden, even in the absence of diffusion. The time dependence of the resulting current pulse is found to be strongly dependent on the ration of the applied field to the field due to the excess carriers. The results of the present theory are compared to those for the transient space-charge limited currents obtained by Many and Rakavy (~ys. Rev. 126, 1980 (1962). (Received 20 July 1966)