D.C. I–V characteristics and steady-state photoconductivity of Au/Pb2CrO5/SnO2 sandwich-structure films under illumination in the visible region |
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Authors: | M M ABDUL-GADER K A WISHAH |
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Affiliation: | (1) Department of Physics, University of Jordan, Amman, Jordan |
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Abstract: | The room temperature d.c. current–voltage (I–V) characteristics of an Au/Pb2CrO5/SnO2 sandwich-structure 1.39 μm thick film
have been measured for d.c. voltages, Vd.c., in the range 0.25 V≤Vd.c.≤5.0 V. These measurements were carried out under both
dark and visible-light illumination conditions. For Vd.c.<2.5 V, the I–V curves of the sample in both dark and light environments
were found to be non-linear and conform to space-charge-limited (SCL) current governed by traps uniformly distributed in energy.
At higher d.c. voltages, a nearly Mott–Gurney V2 behaviour of the dark current has been observed, whereas the I–V behaviour
of the illuminated specimen was a combination of an ohmic conduction and a V2 dependence at low illumination levels and became
highly ohmic at large light intensities. This behaviour can be understood in terms of a reduction in the SCL dark current
in favour of a larger ohmic d.c. photocurrent as a result of neutralization of the majority-carrier space charge by the photogenerated
minority carriers of the electron–hole pairs produced under the illumination with visible light of energy ℏω≅EG(∼2.1–2.3 eV
for the Pb2CrO5 material). The d.c. photocurrent, Iphot, at a fixed d.c. voltage, was found to follow a power-law dependence on light intensity, F, of the form Iphot∝Fγ, with the exponent γ being dependent on the applied d.c. voltage. At the low-voltage side (Vd.c.<1.5 V), γ∼0.5, a value usually obtained when the photoconductivity behaviour is governed by bimolecular recombination mechanisms.
As the d.c. voltage is increased further, γ increases monotonically until it saturates at a value of about 0.9 for d.c. voltages
beyond 3.5 V, where monomolecular recombination processes seem to be more operative with increasing d.c. voltage.
This revised version was published online in November 2006 with corrections to the Cover Date. |
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