The synthesis of epitaxially oriented Si nanowires at high growth rates (>1 microm/min) was demonstrated on (111) Si substrates using Al as the catalyst. The use of high H(2) and SiH(4) partial pressures was found to be effective at reducing problems associated with Al oxidation and nanowire nucleation, enabling growth of high aspect ratio structures at temperatures ranging from 500 to 600 degrees C with minimal tapering of the diameter. Because of the high growth rate observed, the Al catalyst is believed to be in the liquid state during the growth. Four-point resistance measurements and back-gated current-voltage measurements indicate that the wires are p-type with an average resistivity of 0.01 +/- 0.004 Omega-cm. These results suggest that Al is incorporated into the Si nanowires under these conditions at concentrations higher than the solubility limit (5-6 x 10(18) cm(-3)) for Al in Si at 550 degrees C. This work demonstrates that Al can serve as both an effective catalyst and p-type dopant for the growth of Si nanowires.