Minority-carrier injection(dark) metal-polycrystalline silicon contacts

The dependence of minority-carrier injection current Jp on applied forward-bias voltage of metalpolysilicon 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 Jp ¿ exp (q V/KT) for (grain-boundary) recombination limited by the supply of minority carriers, Jp ¿ 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 Jp ¿ exp (3q 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 ÿg, are significant for interface state densities Nis > 1010¿1011cm¿2V¿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 ÿg and low Nis.Minority-carrier injection dominates the dark current (as it does in a p-n junction) for Schottky-barrier height ÿb > 0.8 V, for typical grain size d¿10¿3cm, interface state densities Nis¿1013cm¿2V¿1, and relatively low doping Nd¿1014cm¿3.