Department of Physics and Energy, Materials and Surface Science Institute, University of Limerick, Ireland.
Phys Chem Chem Phys. 2013 Sep 28;15(36):15135-45. doi: 10.1039/c3cp52253a.
We propose a three-step model of electrochemical nanopore formation in n-InP in KOH that explains how crystallographically oriented etching can occur even though the rate-determining process (hole generation) occurs only at pore tips. The model shows that competition in kinetics between hole diffusion and electrochemical reaction determines the average diffusion distance of holes along the semiconductor surface and this, in turn, determines whether etching is crystallographic. If the kinetics of reaction are slow relative to diffusion, etching can occur at preferred crystallographic sites within a zone in the vicinity of the pore tip, leading to pore propagation in preferential directions. Symmetrical etching of three {111}A faces forming the pore tip causes it to propagate in the (remaining) [111]A direction. As a pore etches, propagating atomic ledges can meet to form sites that can become new pore tips and this enables branching of pores along any of the [111]A directions. The model explains the observed uniform width of pores and its variation with temperature, carrier concentration and electrolyte concentration. It also explains pore wall thickness, and deviations of pore propagation from the [111]A directions. We believe that the model is generally applicable to electrochemical pore formation in III-V semiconductors.
我们提出了一个三步模型，用于解释在 KOH 中 n-InP 中的电化学纳米孔形成过程，该模型解释了尽管速率决定步骤（空穴生成）仅发生在孔尖端，但是如何发生晶向刻蚀。该模型表明，空穴扩散和电化学反应之间的动力学竞争决定了空穴沿着半导体表面的平均扩散距离，这反过来又决定了刻蚀是否具有晶向性。如果反应动力学相对于扩散较慢，则可以在孔尖端附近区域内的优选晶面位置发生刻蚀，从而导致优先方向的孔扩展。形成孔尖端的三个{111}A 面的对称刻蚀导致其沿（剩余的）[111]A 方向扩展。随着孔的刻蚀，扩展的原子台阶可以相遇形成可以成为新孔尖端的位点，从而使得孔沿着任何[111]A 方向分支。该模型解释了观察到的孔的均匀宽度及其随温度、载流子浓度和电解质浓度的变化。它还解释了孔壁厚度以及孔扩展偏离[111]A 方向的情况。我们相信该模型通常适用于 III-V 半导体中的电化学孔形成。
