Temperature Dependence of Lateral Charge Transport in Silicon Nanomembranes

Thin sheets of single-crystal silicon (nanomembranes), electrically isolated from a bulk substrate by a dielectric layer, are an exceptional tool for studying the electronic transport properties of surfaces in the absence of an extended bulk. Under UHV, we measure the conductivity, and a back gate allows us to look into the depletion region, where we can determine the minimum conductance. For hydrogen-terminated Si(001) NMs, for which the surface has no conductivity, the minimum conductance decreases with decreasing NM thickness (220-42nm), demonstrating the reduction in carriers for thinner NMs. For the clean Si(2$\times$1)surface, mobile charge exists in the $\pi^{\star}$ surface band [1]. For thicknesses below 200nm surface conduction dominates, rendering the thickness independence of the minimum. We determine a surface charge mobility of $\sim$50cm$^{2}$V$^{-1}$s$^{-1}$[2]. We have measured the temperature dependence of the conductance of a 42nm thick HF treated SiNM. The results show that the Fermi level is pinned 0.21 $\pm0.01$ eV below the conduction band minimum, in agreement with XPS results [3].\\[4pt] [1] P. P. Zhang, et al., Nature 439, 703-706 (2006);\\[0pt] [2] W. Peng, et al., Nature Commun. 4, 1339 (2013);\\[0pt] [3] R. Schlaf, et al., J. Vac. Sci. Technol. A 17, 164 (1999).