Conduction mechanism of metal-free phthalocyanine single crystals as a function of temperature |
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Authors: | Ayona Simon Francis P Xavier |
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Affiliation: | (1) Physics Department, Loyola Institute of Frontier Energy (LIFE), Loyola College, 600 034 Chennai, India |
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Abstract: | Metal-free phthalocyanine (H2Pc) single crystals grown by vacuum sublimation were investigated for their conductivity (both in dark and light). The investigations
consisted of dark- and photo-current variations with (i) applied electric field and (ii) temperature. The applied electric
field ranged from 0·8 kV/cm to 6 kV/cm. The temperature range was from 300°K to around 570°K. The crystals were found to be
photoconductive. Based on activation energies calculated from photoconductivity due to temperature dependence, an energy level
scheme for H2Pc single crystals is proposed. The model consists of two trapping levels within the forbidden gap — one at 0·4 eV below the
conduction band edge from which electrons are thermally excited into the conduction band and the other acts as recombination
centre at 0·3 eV above the valence band edge. The band gap is calculated to be 1·4 eV. Comparative study of the proposed model
with that of earlier investigations on the same crystals of the H2Pc is in good agreement, thereby indicating that H2Pc is thermally stable even at relatively higher temperature as semiconductor. |
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Keywords: | Phthalocyanine photoconductor single crystals |
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