Silicon Nanowires:Electrical, Magnetic And Thermal Properties And Application

Nanowires are an important class of one-dimensional (ID) materials that have been attracting a great deal of interest recently. ID nanomaterials, especially of semi-conductors, usually exhibit unique and superior electronic, optical, thermal, and magnetic properties. Silicon nanowires (SiNWs) are one of the most important ID semiconductors, partly due to their ready implementation in modern industry in established processes. The etching method is one of the optimal technologies to fabricate SiNWs due to simple equipment, low price, high efficiency and good repeatability. SiNWs fabricated by the etching method, which can be seen as core/shell structure, have huge surface-to-volume ratio and coat with amorphous silicon oxide. A large number of unsaturated dangling bonds locate at the interface of core/shell, which generates surface defect states and influence on the electronic, optical, thermal, and magnetic properties of SiNWs. In this paper, these issues were studied and discussed. The mainly works are listed as following.First, the grown mechanism of SiNWs by the etching method has been analyzed. With the analysis of the redox potential of noble metal ions, noble metal, silicon ions and single crystal silicon, noble metal salt as oxidant in the oxidation/reduction reaction is restored and silicon is oxidized as reducing agent. For example, when silicon wafer is etched by the mixed solution with AgNO3and HF, Ag is the cathode of galvanic cell. SiNWs are the channel of electron transmission, which are negatively charged and maintained for difficulty to be oxidized. The surface morphous of SiNWs is serrated, indicating that the etching process followed the principle of silicon anisotropic.Second, the surface paramagnetic defects of SiNWs have been analyzed. With the characterization of SiNWs defects by electron spin resonance (ESR), three different defects are found for the as-grown nanowires. About95%of the spin density is due to the dangling bonds or Pb-defects at the Si/SiO2interface, while5%is caused by the oxide defects, which influence on the mechanism of electric/thermal transmission. At the same time, the surface/interface unsaturated dangling bonds of SiNWs have paramagnetic property, which influence on the magnetic property of the complex material based on SiNWs.Third, the current transmission mechanism of SiNWs and the Schottky junction property of Pt/p-SiNWs are studied. The surface defect states of SiNWs induce the surface depletion layer, by which, Fermi-level is pinned. The experiment data of Pt/p-SiNWs Schottky junction determine that the current transmission mechanism of SiNWs is defect-assisted tunneling, which also explains that the high SiNWs surface states can pin Fermi-level of silicon and improve the electron transport property of SiNWs.Fourth, the magnetic property of SiNWs has been studied. When the size of magnetic material decreases to nano-size, the surface-to-volume ratio and the surface dangling bonds of nanoparticles increase. The nanoparticle is single-domain, which shows the paramagnetic property. If the magnetic nanoparticles are deposited on the surface of SiNWs, The paramagnetic defects and magnetic nanoparticles will interact and affect the magnetic properties of complex material, which are proved by Ni/SiNWs.Fifth, the thermoelectricity property of SiNWs has been studied. The SiNWs fabricated by the etching method are coated with amorphous silicon oxide, which induces a large number of defects. The defect states generate the barrier difference at the interface of core/shell and the depletion region, which significantly decreases the effective area of the thermal transmission, increases the surface phonon scattering rate and improved the thermoelectricity of SiNWs. The thermoelectricity of double-side core/shell SiNWs arrays is studied based on the Raman spectroscopy. The value of thermal conductivity and ZT is0.59Wm-1K-1and1.68, thermal diffusion coefficient is0.007cm2/s.In summary, SiNWs have exhibited good application potential in the field of electrical, thermal, optical and magnetic and are expected to become a key material in nanoelectronic device such as nanosensors.