Experimental Study Of Femtosecond Laser Fabricating Black Silicon

As a new type of semiconductor silicon materials, black silicon has a high absorption in the visible region and has extensive applications in silicon based solar energy cells and optoelectronic detectors. Recently, black silicon material has gained wide attention, and its preparation methods have become one of research highlights in the world. The preparation methods of black silicon are varied, but they have their disadvantages. An efficient approach for enhancing the surface antireflection is proposed, in which, a black silicon is fabricated by a femtosecond laser in alkaline solution. After a series of experiments, expected results were acquired and the effectiveness of the preparation method was verified. In the paper, we did experiments to explore the influence of experimental parameters on the surface morphology and the reflectance of black silicon. These results are of important significance in the control of surface morphology and material surface modification. Main achievements in this paper were listed as follows:1. We set up the experimental device for femtosecond laser fabricating the black silicon in alkaline solution. The jungle-like microstructures are on the surface of the black silicon. Compared to the polished silicon, the black silicon can significantly suppress the surface reflection.2. Experiments were done to explore the relationship between the reflectance of black silicon and the scanning speed. In three kinds of scanning speed, 0.1 mm/s、 0.5 mm/s and 1.0 mm/s, we found that when the laser energy is fixed, the slower the scanning speed is, the lower the reflectance is.3. Through the experiments, we explored the influence of laser energy on the surface morphology and the reflectance of black silicon. The laser energy ranged from 400 μJ to 2000 μJ. Through the analysis of images, we found that the height of jungle-like microstructures increases with the increase of laser energy at first and then decreases with the laser energy continuously increasing. And the reflectance of black silicon decreases and then increases as the laser energy goes up. So we investigated an optimal laser energy( 1400 μJ) for the height of jungle-like microstructures and the reflectance of black silicon samples. In the entire visible region, the average minimum reflectance of the black silicon is about 5.6 %.4. Compared to the Mazur’s method of fabricating black silicon in SF6, fabricating black silicon in alkaline solution via femtosecond laser can avoid the expensive vacuum equipments and dangerous gases such as SF6 and H2 S. So the method is safe for humans and the environment. Compared to the method of fabricating black silicon in sulfuric acid, the method in this paper used the 2 wt% NaOH solution. So it is a low concentration alkaline solution and safe for water and soil. In addition, the method in this paper is simple and easy-operating. Also, the 2wt% NaOH solution is cost-effective and the cost is much less than SF6.