Surface Defects-Induced p-type Conduction of Silicon Nanowires

The fundamental properties of silicon nanowires (SiNWs) are highly dependent on dimension and surface states. Despite many studies of the surface effects on the important properties of SiNWs, the understanding of the interrelation between surfaces and properties remains unclear. Herein we used SiNWs etched from Si wafer as a paradigm to study the relationship of surface states and electrical properties of SiNWs. We showed that, besides hydrogen, SiNW surfaces also consist of adsorbed carbon species, water molecules, and surface defects (P-b center) with a spin density of C-spin = 9.7 x 10(12) mg(-1). Our first-principle calculations revealed that surface defects including P-b, P-b0, and P-b1, similar to H-defect dangling bonds, can provide acceptor levels to trap electrons, and account for the conversion of transport properties from intrinsic to p-type conduction in SiNWs. We further revealed that SiNW with a diameter of tens to 100 rim would show obvious p-type conduction. Additionally, our theoretical simulation showed that water molecule could increase p-type conduction by lowering the defect energy. Low-temperature I-V measurements showed the defect ionization energy in the p-type SiNW at 36.4 meV.