Size Dependence of the Transport Properties of Silicon Nanostructures

Abstract

Silicon devices involving various p-type silicon nanostructures with a fixed length 20 mu m and thickness 40 nm, but with varying width in the range from similar to 100 nm to 20 mu m, were prepared by using the top-down method in order to systematically study the width dependence of their intrinsic transport property. Based on the I(d)-V(g) characteristic measurements, the hole mobility (mu(h)) and concentration (n(h)) were extracted for all nanostructures. For structures of large widths (w > 1.0 mu m, nanoribbon-type), n(h), decreases from 5.5 to 2.4 x 10(17) cm(-3) while mu(h) increases from 160 to 380 cm(2)V(-1)s(-1) as the width narrows down from 20 to 1.0 mu m. Interestingly, however, n(h) and u(h) are found to be correlated such that their product remains nearly constant for this width region, the origin of which is unclear. For structures of small widths (w <= 500 nm, nanowire-type), n(h) remains more or less constant at about 2.4 x 10(17) cm(-3) while mu(h) decreases steadily from 340 to 240 cm(2)V(-1)s(-1) as the width narrows down from 500 to 96 nm. This behavior of mobility degradation with width narrowing in the nanowire region is likely to originate from the enhanced surface scattering effect, but a detailed microscopic theory should be developed to explain this effect quantitatively.