Charge Storage Effect in the Microwave Detected Photoconductive Decay Method*

Abstract

Excess photocarriers excited with a photon beam in a silicon (Si) wafer are annihilated through recombination processes in the surface and bulk regions in the wafer. When a p-type Si wafer has a positive oxide charge on its surface, for example, the charge induces surface potential, forming a depletion layer at the wafer surface. Excess minority carriers are then pulled into the depletion layer and survive there for a relatively long time when the wafer surface is strongly inverted. Survival of the carriers lasts even after the annihilation of the excess carriers in the bulk region. This `charge storage effect', however, disappears when the injection level of the excess carriers is sufficiently high to lower the surface potential, making the surface recombination velocity high as a result.