Doping of amorphous and microcrystalline silicon films deposited by hot-wire chemical vapor deposition using phosphine and trimethylboron

The optical, electronic and structural properties of n-type and p-type doped amorphous (a-Si:H) and microcrystalline (mu c-Si:H) silicon films prepared by hot-wire chemical vapor deposition are studied. Intrinsic a-Si:H films deposited at filament temperatures T-fil similar to 1900 degrees C and 2500 degrees C using equal silane and hydrogen flow rates, and intrinsic mu c-Si:H films deposited either by increasing the hydrogen dilution (F-H2/F(SiH4)greater than or equal to 10) or decreasing the filament temperature (T-fil similar to 1500 degrees C), were doped using phosphine (PH3, n-type doping) or trimethylboron (B(CH3)(3), p-type doping). The dependence of the properties of the doped films on T-fil, dopant-to-silane gas flow ratio, and hydrogen dilution is studied. Both p-type and n-type mu c-Si:H films were prepared and showed dark conductivities sigma(d) similar to 1 Ohm(-1) cm(-1) and activation energies of sigma(d), E-a,E-sigma d similar to 0.05 eV, N-type a-Si:H films were prepared and showed sigma(d) similar to 10(-2) Ohm(-1) cm(-1), E-a,E-sigma d similar to 0.25 eV, whereas p-type doping was less efficient, showing sigma(d) similar to 2 X 10(-6) Ohm(-1) cm(-1), E-a,E-sigma d similar to 0.45 eV. High growth rates (r(d) greater than or equal to 15 Angstrom/s) were obtained for all the a-Si:H doped samples. Tungsten (W) contamination of the amorphous samples was kept below the detection limit of the secondary ion mass spectroscopy analysis (similar to 5 X 10(17) atoms/cm(3)) for all T-fil. The mu c-Si:H samples showed W incorporation close to the detection limit (5-7 X 10(17) atoms/cm(3)) for T-fil greater than or equal to 1900 degrees C. The deep defect density dependence on the dopant-to-silane flow rate ratio was found to be consistent with the defect equilibrium doping model. (C) 1997 American Vacuum Society. [S0734-2101(97)04306-6].