Electrical, thermoelectric, and optical properties of strongly degenerate polycrystalline silicon films

Low-pressure chemical vapor deposited polycrystalline silicon films 0.45 μm thick were doped to strongly degenerate concentrations (1–2×1020 cm−3) by thermal diffusion of phosphorus. Thermoelectric power, Hall effect, and resistivity measurements were made over the temperature range of 80 to 340 K. The thermopower results were in good agreement with single crystal degenerate semiconductor theory. Additionally, these results, in conjunction with the measured carrier concentration, showed that the scattering relaxation time is inversely proportional to the square root of the carrier energy which is indicative of lattice scattering. The temperature dependence of the resistivity was found to be of the form ρ=a+bT. The liner term was attributed to acoustic phonon scattering within the grains and the constant term to lattice mismatch at the grain boundaries. Scattering from grain boundary potential barriers due to carrier trapping appeared to play no significant role although this effect dominates at lower doping concentrations. The index of refraction and absorption coefficient in the near infrared and visible were determined from transmission and reflection measurements of doped and undoped polycrystalline silicon films on quartz substrates.