Reduction of apparent dopant concentration in the surface space charge layer of oxidized silicon by ionizing radiation

We have observed significant reduction of apparent dopant concentration in the surface space charge layer of oxidized silicon resulting from exposure to either an Ar plasma or x rays. Such phenomenon has been found in both p-type (boron doped) and n-type (phosphorus doped) samples. In addition, the magnitude of this reduction depends systematically on the diameter of the gate aluminum dots used to form the metal/SiO2/Si capacitor. In the range (10–60 mil) studied, samples with smaller gate sizes exhibit less dopant reduction. These results may be explained by a model based on the majority-carrier reduction due to the radiation-induced deep electron and hole traps in the surface space charge region of silicon.