Control of Anisotropy in Nanostructured Silicon by Linearly Polarized Light

纳米结构多孔硅样品经线偏振光照射后，在电化学蚀刻过程中表现出光学各向异性。本课题旨在阐明各向异性的形成机制，并将其应用于新型光学器件。主要研究结果如下：折射率各向异性的观察几个研究小组根据光致发光的线偏振度的结果报道了多孔硅层的光学各向异性。在这个项目中，我们首次观察到折射率的显著各向异性。各向异性使得最大折射率出现在与最大线偏振度相差90度的方向上。这可以通过假设大硅结构负责折射率各向异性，而小结构控制发光各向异性来解释。激发波长对发光各向异性的影响我们观察到，激发波长对发光各向异性的影响很大。我们的实验结果表明，这不是由于氧化物发光的影响，而是由于深度不均匀性造成的。红外激光辐照样品强各向异性的实验观察与计算机模拟我们采用较高强度的1.06 μm Nd: YAG激光作为照明光源，获得了很强的发光各向异性。基于线性振子平面分布的二维模型，计算机模拟可以很好地再现这一结果。阳极氧化条件的影响我们已经证明，使用HF浓度低至0.1%的极稀HF溶液可以得到发光多孔硅样品。然而，在这些样品中没有观察到明显的发光各向异性，这表明阳极氧化电流密度在很大程度上影响了各向异性的形成。少

Nanostructured porous silicon samples exhibit optical anisotropy after being irradiated with linearly polarized light while they are etched electrochemically. This research project aims at clarifying the mechanism for the formation of anisotropy and applying this to novel optical devices. Major results are summarized as follows:1. Observation of anisotropy in refractive indicesThe optical anisotropy in porous silicon layers has been reported by several research groups based on their results on the degree of linear polarization in photoluminescence. In this project, we have observed a significant anisotropy in refractive indices for the first time. The anisotropy is such that the largest index appears in a direction 90-degree off that of the largest degree of linear polarization. This can be explained by assuming that large silicon structures are responsible for refractive index anisotropy while small structures govern luminescence anisotropy.2. Effect of excitation wavelengths on lumin … More escence anisotropyWe have observed that the luminescence anisotropy is affected largely by the excitation wavelength. Our experimental results show that this is not due to the effect of luminescence from oxides but is originating from depth inhomogeneity.3. Experimental observation and computer simulation of the strong anisotropy in samples irradiated with infrared laser lightWe have used a 1.06-μm Nd : YAG laser of relatively high intensity as an illumination source and obtained very strong luminescence anisotropy. The result can be reproduced well by computer simulation based on a two-dimensional model in which linear oscillators are distributed in a plane.4. Effect of anodization conditionsWe have shown that luminescent porous silicon samples can be obtained by using extremely dilute HF solutions with HF concentrations down to 0.1%. No significant luminescence anisotropy, however, has been observed in these samples, implying that anodization current density largely affects the formation of anisotropy. Less