Uniform Silicon p-n Junctions. II. Ionization Rates for Electrons

Charge multiplication as a function of reverse bias has been studied in a number of uniform silicon p-n junctions (junctions free from defects which promote local avalanche breakdown sites). From the multiplication characteristics new data have been derived for the field dependence of the ionization rate (α) for electrons. As previously found in junctions containing dislocations, α obeys the empirical relation α=α∞ exp (−b/E), where α∞ and b are constants and E is the field. Thus, this law is not simply a consequence of distortions to the junction introduced by dislocations or other microplasma-inducing defects. The ionization rates and breakdown voltages for the uniform junctions can be made consistent with older data (for nonuniform junctions) if the junction fields, as determined from capacitance measurements, in the new junctions are multiplied by 0.65. The most obvious interpretation of this experimental fact is that breakdown is made relatively easier at defects because the field is actually higher by a factor of 1.55. Possible causes of such an enhancement are discussed together with alternative hypotheses for the different ionization rates.