Carrier Doping of Silicon Nanowires Synthesized by Laser Ablation
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0963-Q10-37
Carrier Doping of Silicon Nanowires Synthesized by Laser Ablation Naoki Fukata1, Naoya Okada2, Satoshi Matsushita2, Takao Tsurui3, Shun Ito3, Jun Chen1, Takashi Sekiguchi1, Noriyuki Uchida2, and Kouichi Murakami2 1 Advanced Electronic Materials Center, National Institutefor Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan 2 Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, 305-8573, Japan 3 Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Sendai, 980-8577, Japan
ABSTRACT Boron (B) doped silicon nanowires (SiNWs) were synthesized by laser ablation. Local vibrational modes of B in SiNWs were observed by micro-Raman scattering measurements at room temperature. Broadening due to a coupling between the discrete optical phonon and a continuum of interband hole excitations was also observed in the Si optical phonon peak. This is called Fano broadening. These results prove that B atoms were doped in substitutional sites of crystalline Si core of SiNWs during laser ablation. INTRODUCTION One-dimensional silicon nanowires (SiNWs) are of great interest in the fields of both fundamental and application research since they exhibit novel physical properties, and thus have wide potential applications in nanoscale electronic devices and optics. Various demonstrations have been reported for future application of SiNWs such as electronic and optical devices. To realize such devices, the characterization and impurity-doping of SiNWs are of important subjects. B doping in SiNWs have been investigate by resistivity and conductance measurements [1-5]. Raman scattering are very useful methods for SiNWs since the bonding structures and the site of dopant atoms in SiNWs can be investigated. The methods are also sensitive for Si optical phonon, which gives valuable information about crystallinity, stress, and diameter of SiNWs [6,7]. Very recently, we could get strong evidence about B doping in SiNWs by micro-Raman scattering measurements, namely, the observation of local vibrational modes of B and that of Fano broadening for B-doped SiNWs [8]. In this report, we show the progress about B doping in SiNWs in addition to our previous results. EXPERIMENT SiNWs were synthesized by laser ablation of a Si target with nickel as a metal catalyst and B as dopant impurities. Three kinds of targets, namely, Si89Ni1B10, Si98Ni1B1, and Si99Ni1 targets were used. They were placed in a quartz tube heated at 1200˚C in a flowing of Ar gas (50 sccm) and that of H2 gas (10 sccm). A frequency-doubled NdYAG laser (532 nm, 7 ns pulse width, 10 Hz, 150 mJ/pulse) was used to ablate these targets. In this experiment, SiNWs were directly collected on a SiO2 substrate to avoid Si substrate effects for Raman scattering measurements. The growth mechanism of SiNWs is VLS (Vapor-Liquid-Solid) growth. MicroRaman scattering measurements were performed at room temperature (RT) with a 100x objective
and a 532-nm excitation light at a power of 0.02 mW to avoid the local heating effect due to the excitation
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