Overall current-voltage characteristics of space charge controlled currents for thin films by a single carrier species

The Mott-Gurney equation (Child's law) has been frequently applied to measure the mobility of carrier transport layers. One of the main assumption in the Mott-Gurney theory is ignoring the diffusive currents. It was not obvious, however, whether the diffusive currents can be ignored for thin carrier transport layers. We obtained the current-voltage relation using analytical solutions of drift-diffusion equation coupled with the Poisson's equation. The integration constants were numerically determined using nonlinear equations obtained from boundary conditions.A simple analytical relation between the voltage and current was also derived. The analytical equation improved over the Mott-Gurney equation when the voltage is between 0.1 and 2 [V] at room temperature. By using published data, we show that both the mobility and the layer thickness can be simultaneously obtained by applying the analytical expression. The effect of diffusion on the current-voltage relation is explained by the movement of the virtual electrode formed by space charge accumulation.

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