Atomic analyzis and photocurrent studies of isolated sub-100 nm diameter silicon nanowires

n-doped Si NWs were synthesized by the vapor-liquid-solid mechanism using the chemical vapor deposition (CVD) technique.The nanowires were grown to a nominal length of 10 $\mu $m with a diameter ranging typically from 60 to 110 nm. Atom Probe Tomography analyzes evidence a gradient of concentration of the phosphorous atom dopants, inducing a built-in potential accros the nanowires. Photocurrent on isolated nanowires was performed with a monochromator source. Depending on the light energy and on the nanowire diameters, we measure various absorption thresholds. Calculations have been performed on a periodic array of wires of varying diameters and with different periodicity by using a Finite Difference Time Domain (FDTD) method. The results evidence a clear dependence of the optical absorption with the nanowire diameters. This work was supported by DGA REI contract N\r{ }2008.34.0031.