The phase selection law in the growth of hexagonal diamond silicon nanowires by controlling chemical potential

Abstract

Large-scale and whole hexagonal diamond silicon nanowires (h-SiNWs) were synthesized with aluminum-gold (Al–Au) alloy-catalytic assistance to reduce the nucleation barrier by regulating the chemical potential. Here, we demonstrate the effect of the catalyst on the structure in silicon nanowires by correlating the experimental observations with a theoretical interpretation based on thermodynamics. It was found that high chemical potential is necessary to enhance the nucleation of the hexagonal diamond phase, and the addition of Al into the Au catalyst can increase the supersaturation of silicon atoms in the catalyst and reduce the contact angle of solid-liquid to tune the chemical potential. When the supersaturation is high enough and the alloy catalyst is almost perpendicular to the top of the nanowire, the hexagonal diamond phase is more likely to appear than the cubic phase, whereas others are not. Additionally, a 1319 nm photodetector was fabricated using the h-SiNWs network with a smaller band gap and a lower conductivity compared with cubic silicon nanowires (c-SiNWs), whose dark current is as low as 5.03 × 10 −12 A with a high responsivity of 0.5 A⋅ W −1 at an applied bias of 1 V.