基于第一性原理计算的掺杂柔性黑硅吸收光谱特性分析

针对宽波段微型光谱仪缺乏宽波段柔性探测器这一难题，提出了一种在紫外-可见-近红外波段内具有高吸收效率的掺杂柔性黑硅作为探测器吸光材料。首先，基于第一性原理计算了S和F元素掺杂后柔性黑硅的电子结构、能带结构和紫外-可见-近红外波段的光学吸收特性，得到了不同元素及浓度掺杂时，柔性黑硅的光学吸收系数。其次，将第一性原理计算结果与时域有限差分算法相结合，建立了柔性黑硅的吸收光谱模型。结果表明，掺入S和F元素后柔性黑硅的能带带隙均减小，吸收截止波长发生红移，且掺杂浓度越高，光学吸收系数越大。在1 500 nm波长处，50%浓度的S元素掺杂黑硅的吸光系数是1.5%浓度的S元素掺杂黑硅的吸光系数的8.3倍，50%浓度的F元素掺杂黑硅的吸光系数是1.5%浓度的F元素掺杂黑硅的吸光系数的3倍。在相同掺杂条件下，表面具有小尺寸微结构的柔性黑硅在近红外波段具有最高的吸收效率。最后，测试了制作的柔性黑硅样品，其吸光效率在紫外-可见波段高于95%，在近红外波段为70%~80%。

Study on the Absorption Spectrum Properties of Flexible Black Silicon Doped with Sulfur and Fluorine Based on First-Principles

It is quite urgent to need a flexible photodetector in the ultraviolet-visible-near infrared region for building a miniaturization broadband spectrometer. In the present paper, one kind of flexible black silicon doped with sulfur and fluorine was proposed and the optical absorption spectrum was investigated in broadband region. Firstly, the electronic structure, band structure and the optical absorption properties of the flexible black silicon doped with sulfur and fluoride were calculated using the first-principles pseudo potential calculations based on density-functional theory. Then, the absorption spectrum model of the flexible black silicon was built based on both the first-principles and finite domain time difference method. The results show that the cut-off wavelength has a red shift as the band gap of doped material becomes narrower. The higher the doping concentration is, the higher the optical absorption coefficient is obtained. The absorption coefficient of flexible black silicon doped with 50% sulfur is 8.3 times higher than that of 1.5% sulfur doping sample at the wavelength of 1 500 nm while the ratio turns to be 3 times when doped with 50% and 1.5% fluoride. The black silicon with small-size surface microstructure has the highest absorptance in the near-infrared region at the same doping concentration of 50%. Finally, a sample of flexible black silicon was fabricated by the femtosecond laser auto scanning system. The test results indicate that the absorptance of the sample is higher than 95% both in the ultraviolet and visible region and is fluctuated from 70% to 80% in the near-infrared region. It shows that as a novel light-absorbing material in broadband region the flexible black silicon doped with Sulfur and Fluorine has an potential application in exploring miniaturization broadband spectroscopy.