The electrical properties of polycrystalline silicon films

Abstract

Boron doses of 1×10¹²–5×10¹⁵/cm² were implanted at 60 keV into 1‐μm‐thick polysilicon films. After annealing at 1100 °C for 30 min, Hall and resistivity measurements were made over a temperature range −50–250 °C. It was found that as a function of doping concentration, the Hall mobility showed a minimum at about 2×10¹⁸/cm³ doping. The electrical activation energy was found to be about half the energy gap value of single‐crystalline silicon for lightly doped samples and decreased to less than 0.025 eV at a doping of 1×10¹⁹/cm³. The carrier concentration was very small at doping levels below 5×10¹⁷/cm³ and increased rapidly as the doping concentration was increased. At 1×10¹⁹/cm³ doping, the carrier concentration was about 90% of the doping concentration. A grain‐boundary model including the trapping states was proposed. Carrier concentration and mobility as a function of doping concentration and the mobility and resistivity as a function of temperature were calculated from the model. The theoretical and experimental results were compared. It was found that the trapping state density at the grain bound was 3.34×10¹²/cm² located at 0.37 eV above the valence band edge.