Large, light-induced capacitance enhancement in semiconductor junctions simulated by capacitor-resistor nets

Abstract

The equivalent circuit simulation of random resistors-capacitors (R-C) net, modified to include large capacitors interfacing between the random R-C bulk and the electrode surface, shows an enhancement of 3 orders of magnitude of the apparent real dielectric constant at low frequencies upon an introduction of resistors percolating paths in the bulk. The appearance of the bulk R-percolating paths can represent the photo-generated high conductivity state of semiconductors bulk, an effect supported by the experimental observation that, in parallel with the photo-enhancement of the real dielectric constant, its imaginary part is strongly enhanced as well. The addition of the photo-generated charge carriers strongly enhances bulks electrical conductivity, effectively confining the space charge region to the interface between bulks edge and the electrode. That could be a simple phenomenological explanation for the apparent dielectric constant enhancement upon illumination in photocells, not involving elaborate physical models.