Modeling MOS capacitors to extract Si—SiO2interface trap densities in the presence of arbitrary doping profiles

A conventional Poisson solver has been used to calculate the quasi-static capacitance of an MOS capacitor. The effects of an energy dependent Si-SiO2interface trap density and of an arbitrary silicon substrate doping profile have been included. This model has been used to calculate the quasi-static characteristics and to compare them with those measured using Kuhn\´s technique for as-received and for gamma-irradiated p-type and n-type silicon MOS capacitors. The substrate doping profiles were obtained from high-frequency curves. Experimental and theoretical curves were made to agree by varying the voltage offset due to fixed oxide charge and both the magnitude and the energy distribution of interface trapped charge. The distributions of interface traps that gave the best fits between experiment and theory are donor-like with a peak 0.1 eV below midgap for the p-type and 0.1 eV above midgap for the n-type silicon MOS capacitors. The predicted curves are insensitive to increases in the density of interface traps near the band edge.