Effect of grain boundary on electrical characteristics in B- and P-doped polycrystalline Si_{1-x -y}Ge_xC_y film deposited by ultraclean LPCVD

The effect of grain boundary on electrical characteristics in B- and P-doped polycrystalline (poly) Si_{1-x -y}Ge_xC_y films was investigated. Poly-Si_{1-x -y}Ge_xC_y films were deposited on thermally oxidized Si(100) at 500-650 °C in a SiH₄-GeH₄-SiH₃CH₃-H₂ gas mixture by an ultraclean hot-wall low-pressure chemical vapor deposition. B and P were doped into the films by ion implantation and diffusion by heat-treatment. The electrical properties are characterized by grain size, width of disordered region near grain boundaries, carrier trap density and the amount of impurity segregation at grain boundaries. In the B-doped poly-Si_{1-x -y}Ge_xC_y films heat-treated at 900 °C, the increase of carrier concentration n_poly and the decrease of resistivity ρ_poly with Ge addition are caused by the narrowing of the width of disordered regions, i.e., crystallization of disordered regions induced by Ge atoms. The decrease of n_poly and the increase of ρ_poly with C addition are explained by the suppression of crystallization of disordered region due to C atom segregation at grain boundaries. In the P-doped poly-Si_{1-x -y}Ge_xC_y films, it is found that n_poly and ρ_poly are influenced by P atom segregation at grain boundaries due to lowering solid solubility of P in grain by the existence of Ge.