Obtaining Uniform Dopant Distributions in VLS-Grown Si Nanowires

Semiconducting nanowires grown by the vapor-liquid-solid method commonly develop nonuniform doping profiles both along the growth axis and radially due to unintentional surface doping and diffusion of the dopants from the nanowire surface to core during synthesis. We demonstrate two approaches to mitigate nonuniform doping in phosphorus-doped Si nanowires grown by the vapor-liquid-solid process. First, the growth conditions can be modified to suppress active surface doping. Second, thermal annealing following growth can be used to produce more uniform doping profiles. Kelvin probe force microscopy and scanning photocurrent microscopy were used to measure the radial and the longitudinal active dopant distribution, respectively. Doping concentration variations were reduced by 2 orders of magnitude in both annealed nanowires and those for which surface doping was suppressed.