Predicted Effect of Exponential Charging Profiles on Photoinjected Currents in Silicon Dioxide

Abstract

Photocurrents produced by electron photoinjection over a contact interface barrier into an insulator are significantly affected by any charging which occurs in the insulator. The photoinjection is most seriously affected by negative charging near the maximum of the interface barrier potential. In this paper normalized photocurrent solutions are derived for negative exponential charging distributions at the injecting interface. With the aid of the normalized solutions the photocurrent I‐vs‐V measurements can be used to directly determine (or approximate to) the peak charge density at the interface (N 0) and the exponential decay distance (xc ). A plot of the ratio of the barrier distance with charging (x 0) to the barrier distance without charging (x 00) vs voltage has a maximum for x 0 equal to 2xc . The N 0 value may then be calculated from the quadratic dependence of N 0 on the magnitude of the maximum ratio of x 0/x 00. Total electron charge densities (N 0 xc ) as low as 109 cm−2 can be measured.