Effects of temperature on electronic properties of nickel phthalocyanine thin sandwich film structures

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Abstract
The effects of temperature on electronic properties of thin sandwich film structures of Au/NiPc/Au were investigated for both freshly prepared and heat-treated sample devices at a pressure of 10−4 Pa. Current density–voltage characteristics at room temperature for both types of sample indicate ohmic conduction at low voltages, followed by space charge limited conduction in the higher voltage range. The latter has been found to be controlled by an exponential trap distribution above the valence band edge. Experimental results indicate that conductivity is critically dependent upon the film annealing history. Hole and trapping parameters for both the fresh and heat-treated sample were also evaluated yielding the following values: Trap concentration per unit energy range P0=1.03×1044 J−1 m−3, total concentration of traps Nt(e)=1.70×1024 m−3, concentration of thermally generated holes p0=1.30×1014 m−3, for the freshly prepared sample, and P0=2.50×1044 J−1 m−3, Nt(e)=4.10×1024 m−3, p0=5.60×1012 m−3, for the heat-treated sample. Measurements of current density over a temperature range of 250–430 K were also performed yielding a hole mobility value of μ=7×10−5 m2 V−1 s−1.