Interpretation of dc characteristics of phosphorus-doped polycrystalline silicon films: Conduction across low-barrier grain boundaries

Abstract

Current–voltage curves of phosphorus-doped polycrystalline silicon films of Lee and Cheng are reanalyzed with the same trapping model of thermionic and thermionic-field emission across symmetrical Schottky barriers between grains. The analysis yields unexpectedly low values of the effective number of grains Neff in the conducting path. Values of Neff/Ngeo decreases from 0.5 at 20 K to 0.1 at 300 K, where Ngeo =(film length)/(typical grain size). A dc conduction model is proposed. Carriers in phosphorus-doped polysilicon films travel extensively across low-barrier grain boundaries, where electrons from segregated phosphorus are abundant enough to fill most of the electron traps. The model can also explain an observed current–temperature relation i∝T3 at low bias voltages and yield values of barrier resistance comparable to reported data on polycrystalline silicon neutron-transmutation doped with phosphorus measured by a small-area traveling potential probe.