Universal disorder in the microwave conductance spectra of doped silicon nanowire arrays

Microwave conductance spectra of doped silicon nanowire (SiNW) arrays were measured from 0.1 to 50 GHz at temperatures between 4 K and 293 K. SiNWs were synthesized by VLS growth, assembled into arrays on co-planar waveguides and measured using microwave vector network analysis. The complex conductance of the arrays was found to increase with frequency at all temperatures as $f^{s}$, with 0.25 $<$ s $<$ 0.4, and to agree with the expected Kramers-Kronig relations. This AC conductance is consistent with behavior found universally in disordered systems. The likely cause is disorder from Si/SiO$_{x}$ interface states dominating the conduction due to the high surface-to-volume ratio of the nanowires. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. Penn State authors acknowledge partial support from NSF DMR-0213623 and NSF NIRT ECCS-0609282.