MINORITY-CARRIER INJECTION (DARK) METAL-POLYCRYSTALLINE SILICON CONTACTS.

The dependence of minority-carrier injection current J//p on applied forward-bias voltage of metal-polysilicon contacts has been calculated within a general treatment of the recombination at grain boundaries. A uniform distribution of interface states in energy at the grain boundaries is assumed throughout. It is found approximately that J//p approximately equals exp (q V/KT) for (grain-boundary) recombination limited by the supply of minority carriers, J//p approximately equals exp (q V/KT) or exp (q V/2KT) for high and low grain-boundary interface state densities for recombination limited by the supply of majority carriers, and J//p approximately equals exp (3 q V/4KT) for intrinsic recombination (limited equally by holes and electrons). Electrostatic effects of grain-boundary interface states, resulting in a bias dependence of grain-boundary barrier height phi //g, are significant for interface state densities N//i//s greater than 10**1**0-10**1**1 cm** minus **2 V** minus **1, depending upon the doping within the grains. The effective diffusion length for the injected minority carriers also shows an appreciable bias dependence, especially for intrinsic recombination, and for majority-carrier limited recombination at high phi //g and low N//i//s. Minority-carrier injection dominates the dark current (as it does in a p-n junction) for Schottky-barrier height phi //b greater than 0. 8 v, for typical grain size d congruent 10** minus **3 cm, interface state densities N//i//s approximately equals 10**1**3 cm** minus **2 V** minus **1, and relatively low doping N//d congruent 10**1**4 cm** minus **3.