Sheng Xing, Johnson Steven G, Michel Jurgen, Kimerling Lionel C
Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Opt Express. 2011 Jul 4;19 Suppl 4:A841-50. doi: 10.1364/OE.19.00A841.
We numerically investigate the light-absorption behavior of thin-film silicon for normal-incident light, using surface textures to enhance absorption. We consider a variety of texture designs, such as simple periodic gratings and commercial random textures, and examine arbitrary irregular periodic textures designed by multi-parameter optimization. Deep and high-index-contrast textures exhibit strong anisotropic scattering that is outside the regime of validity of the Lambertian models commonly used to describe texture-induced absorption enhancement for normal incidence. Over a 900-1100 nm wavelength range, our optimized surface texture in two dimensions (2D) enhances absorption by a factor of 2.7 πn, considerably larger than the original πn Lambertian result and exceeding by almost 50% a recent generalization of Lambertian model for periodic structures in finite spectral range. However, the πn Lambertian limit still applies for isotropic incident light, and our structure obeys this limit when averaged over all the angles. Therefore, our design can be thought of optimizing the angle/enhancement tradeoff for periodic textures.
我们通过数值方法研究了垂直入射光下薄膜硅的光吸收行为，利用表面纹理来增强吸收。我们考虑了多种纹理设计，如简单的周期性光栅和商业随机纹理，并研究了通过多参数优化设计的任意不规则周期性纹理。深且高折射率对比度的纹理表现出强烈的各向异性散射，这超出了通常用于描述垂直入射时纹理诱导吸收增强的朗伯模型的有效范围。在900 - 1100纳米波长范围内，我们优化的二维表面纹理将吸收增强了2.7πn倍，远大于原始的πn朗伯结果，并且比最近在有限光谱范围内对周期性结构的朗伯模型推广结果高出近50%。然而，πn朗伯极限仍然适用于各向同性入射光，并且我们的结构在所有角度上平均时遵循该极限。因此，我们的设计可以被认为是优化了周期性纹理的角度/增强权衡。
