LIGHT-CONTROLLED ELECTRIC-FIELDS IN A HIGH-RESISTANCE MSM STRUCTURE WITH DEEP IMPURITY LEVELS .2. HIGH INTENSITIES

The influence of deep levels on the photoelectric effect in a strongly biased, high-resistance, symmetric MSM structure illuminated by monochromatic light (hv greater than or similar to E(g)) is examined theoretically. The system of equations consisting of the continuity equations in the diffusion-drift approximation and the Poisson equation is solved. Thermionic emission of carriers across the metal-semiconductor surface at the boundaries is taken into account. ResultS are reported for a Au-CdTe-Au structure with a single impurity level, which is manifested in the interior as a hole trapping level. Even in the presence of an impurity, at intensities above a certain critical value, there is an inversion (i.e., change in sign) of the electric field in a thin layer near the anode. Beyond this inversion region is a quasineutral region, whose width increases with the intensity and decreases significantly with increasing N(t). The latter behavior is due to a recombination of carriers in the potential well for electrons. With increasing N(t), the field at the cathode decreases. The current-intensity characteristic is qualitatively the same as in the absence of impurities. However, the value of the current, which is limited by the space change, and the rate of increase of the current at intensities above the inversion level decrease significantly because holes are trapped by impurity levels in the interior of the structure. At small values of N(t), the magnitude of the space-charge-limited current falls off linearly with increasing N(t). The current-voltage characteristic is linear at low voltages V. It reaches saturation at high values of V. The saturation current is proportional to the illumination intensity but independent of N(t). As V is reduced, the E(x) profile in the interior becomes nonmonotonic. A region with d2E/dx2 > 0 arises near the anode. The width of the inversion region increases. At small values of V and N(t) it can reach tens of microns.