Vertically Aligned Various Lengths Doped-Silicon Microwire Arrays by Repeated Selective Vapor-Liquid-Solid Growth

Abstract

We have proposed a growth technique of various lengths, 2-4 mum diameter, conductive-silicon micowire arrays, by repeated vapor-liquid-solid (VLS) growth of n-type silicon, using Au as the growth catalyst and a mixture gas of 1% PH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> with 100% Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> as the silicon gas source. We obtained a longer 100 mum-length silicon wire by both the first growth of 50 mum-length wire and an additional growth of 50 mum-length wire over the first wire, while a shorter 50 mum-length silicon wire had simultaneously been grown from the substrate by the additional growth. We investigated the junction existing at the interface between the first and the second n-type silicon wire bodies. Current I-voltage V measurements on a two-step grown n-type/n-type silicon wire exhibit linear behavior with the overall resistance of 850 Omega, confirming no electrical barrier at the interface junction. Several bending tests on the wires with the junction confirmed no significant change in the mechanical properties of the wire. We developed the microwire arrays for a potential application to investigations of multiple cell layers in brain cortex or retina (Fig. 1). We also believe that the proposed technique becomes new approach to construct three-dimensional devices in MEMS fields.