Relaxation of photodielectric effect in Pb 3 O 4 layers
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PHOUS, VITREOUS, POROUS, ORGANIC, AND MICROCRYSTALLINE SEMICONDUCTORS; SEMICONDUCTOR COMPOSITES
Relaxation of Photodielectric Effect in Pb3O4 Layers V. T. Avanesyan^ and E. P. Baranova Herzen State Pedagogical University of Russia, St. Petersburg, 191186 Russia ^e-mail: [email protected] Submitted January 25, 2007; accepted for publication February 5, 2007
Abstract—Experimental data on the kinetics of the photodielectric effect in layers of red lead (Pb3O4) are reported. The photocapacitive properties and dielectric loss under photoexcitation have been studied with the spectral composition of light varied at low frequencies of the measuring field. The dielectric parameters attain steady values long after light is switched on (off). The relationship of the photodielectric phenomena with structural features of the semiconductor and, in particular, with the presence of lone pair electrons of Pb2+ cations is discussed. PACS numbers: 73.50.Pz, 77.22.Gm, 81.40.Tv DOI: 10.1134/S1063782607100144
1. INTRODUCTION
2. EXPERIMENTAL
Red lead Pb3O4 is distinguished among components of the lead oxide series by the stability of its phase composition in thin layers, photoelectric sensitivity in the visible spectral range, and pyroelectric and ferroelectric properties [1]. Its high resistivity, combined with a high density of deep localized states, enables the use of the oxide Pb3O4 in electret structures.
The measurements were performed with red lead layers deposited using powdered Pb3O4 of analytically pure grade. The layers were deposited onto glass substrates with an electrically conducting transparent layer of tin dioxide SnO2 as the bottom electrode and a metal foil as the top electrode. The binder, an organosilicon lacquer, formed a highly transparent high-resistivity light-insensitive layer between the photoconducting grains of polycrystalline Pb3O4. The layers obtained had a thickness of about 50 µm and an area of ~20 cm2.
Charge processes underlie the operation of most of semiconductor optoelectronic and radio engineering devices by determining their most important performance parameters. Preliminary studies have shown that the electrical conduction in the oxide Pb3O4 is accompanied by intense polarization processes both in measurements in the dark and under photoexcitation [2]. An effective way to determine the electronic structure and the nature of localized states is an experimental study of the dielectric relaxation under the effect of various external factors. The rate of carrier generation from trap levels and the capture to these levels affect the response time of electronic devices fabricated from high-resistivity materials. A study of the photodielectric effect (PDE) [3] is an informative method for measuring the photoconductivity in ac electric fields. This method allows analysis of the behavior of carriers with a limited, for some reason, possibility of motion in a semiconductor. In a number of studies, PDE has been used to find out whether or not parameters of localized states in the energy gap of a semicon
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