Vinzons Lester U, Shu Lei, Yip SenPo, Wong Chun-Yuen, Chan Leanne L H, Ho Johnny C
Department of Electronic Engineering, City University of Hong Kong, Kowloon, Hong Kong.
Department of Physics and Materials Science, City University of Hong Kong, Kowloon, Hong Kong.
Nanoscale Res Lett. 2017 Dec;12(1):385. doi: 10.1186/s11671-017-2156-z. Epub 2017 Jun 2.
Many potential applications of porous silicon nanowires (SiNWs) fabricated with metal-assisted chemical etching are highly dependent on the precise control of morphology for device optimization. However, the effects of key etching parameters, such as the amount of deposited metal catalyst, HF-oxidant molar ratio (χ), and solvent concentration, on the morphology and etching kinetics of the SiNWs still have not been fully explored. Here, the changes in the nanostructure and etch rate of degenerately doped p-type silicon in a HF-HO-HO etching system with electrolessly deposited silver catalyst are systematically investigated. The surface morphology is found to evolve from a microporous and cratered structure to a uniform array of SiNWs at sufficiently high χ values. The etch rates at the nanostructure base and tip are correlated with the primary etching induced by Ag and the secondary etching induced by metal ions and diffused holes, respectively. The HO concentration also affects the χ window where SiNWs form and the etch rates, mainly by modulating the reactant dilution and diffusion rate. By controlling the secondary etching and reactant diffusion via χ and HO concentration, respectively, the fabrication of highly doped SiNWs with independent control of porosity from length is successfully demonstrated, which can be potentially utilized to improve the performance of SiNW-based devices.
通过金属辅助化学蚀刻制备的多孔硅纳米线（SiNWs）的许多潜在应用高度依赖于对形态的精确控制以优化器件。然而，诸如沉积金属催化剂的量、HF-氧化剂摩尔比（χ）和溶剂浓度等关键蚀刻参数对SiNWs的形态和蚀刻动力学的影响仍未得到充分探索。在此，系统地研究了在具有化学沉积银催化剂的HF-H₂O-H₂O₂蚀刻系统中简并掺杂p型硅的纳米结构和蚀刻速率的变化。发现在足够高的χ值下，表面形态从微孔和坑洼结构演变为均匀排列的SiNWs阵列。纳米结构基部和尖端的蚀刻速率分别与由Ag引起的一次蚀刻以及由金属离子和扩散空穴引起的二次蚀刻相关。H₂O₂浓度也影响SiNWs形成的χ窗口和蚀刻速率，主要是通过调节反应物稀释和扩散速率。通过分别经由χ和H₂O₂浓度控制二次蚀刻和反应物扩散，成功展示了能够独立控制孔隙率与长度的高掺杂SiNWs的制备，这有可能用于改善基于SiNWs的器件的性能。
