Different mechanisms affecting the inversion layer transient response

The transient response of the MOS capacitance after the application of a large depleting voltage can be caused by three different mechanisms depending on the distribution of the electric field between the silicon and the oxide. The three different cases were distinguished by measurements of the temperature dependence and the voltage dependence of the relaxation behavior. Relaxation due to thermal generation of carriers prevails at low electric fields, relaxation via oxide states occurs at medium fields, and relaxation by avalanche effects predominates at high fields. From the case where thermal relaxation is predominant the effective lifetime of minority carriers in the depletion region and the surface recombination velocity could be determined. At low temperatures (&sim100°K) where most frequently no relaxation occurs in the dark, light-induced relaxation phenomena were studied. Only light with energies larger than the Si band gap causes relaxation.