Time-resolved measurement of the escape of charge carriers from a Coulombic potential well by diffusional motion

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Abstract
The irreversible escape of charge carriers from the bottom of a coulombic potential well over the barrier by diffusional motion has been measured, for the first time, directly as a rise time of 1 ns time-resolved current transients in anthracene single crystals with electrolytic contacts. The observed steep decrease in the characteristic escape time down to 1 ns, with rising electric field up to 1×105 V cm−1, is in excellent agreement with the predictions of a stationary one-dimensional charge carrier injection model with generalized boundary conditions. The electric field dependence of the rate constant for escape cannot be approximated simply by an exponential dependence on the barrier height, as in the familiar Schottky correction for the case of electron emission or in the Poole–Frenkel formula for change carrier escape from a charged trap. As a side result, the hole mobility in the c′ direction of anthracene single crystals has been found constant μ = 0.85±0.05 cm2 V s−1 up to an electric field strength of 5±105 V cm−1 at room temperature.