A polysilicon—Silicon n-p junction

Phosphorus-doped polycrystalline silicon is grown in an epitaxial reactor by the reduction of a hydrogen-diluted silane-phosphine mixture passing over a substrate heated to 800°C. The influence of the phosphine-silane ratio on growth rate, electrical resistivity, active donor concentration, and Hall mobility is examined. It is found that phosphine inhibits growth rate at 800°C to a lesser degree than it does at lower growth temperatures. Growth rate progressively drops to 0.6 of the undoped value as the phosphine-silane ratio is increased to 10^-1. Resistivity drops from 1 to 10^-3Ω. cm as active phosphorus concentration varies between 10¹⁸and 4 × 10²⁰cm^-3, while Hall mobility rises from 4 to 30 cm²/ V.s. Diodes are formed between the grown polysilicon layers and the single-crystal p-type silicon substrates. They are found to have recombination currents critically dependent on the phosphine/ silane ratio during growth of the polysilicon. As this ratio increases above 10^-5, recombination decreases, while mobility in the polysilicon increases. These results support the "dopant segregation" theory of conduction in polysilicon. For ratios of 10^-3to 10^-2the diodes obtained showed a recombination factor approaching those of diffused diodes and are useful devices, for example, as the emitter-base junction of a shallow-base high-frequency, bipolar transistor.