Preparation And Near-infrared Detection Research Of Black Silicon

Due to its special surface morphology and good broad-spectrum optical absorption, the emergence of black silicon has attracted widespread concern both at home and abroad. Currently, researches on new material in the field of solar cell and photovoltaic have been gradually thorough.We fabricate black silicon by metal-assisted chemical etching, and the studies have shown that sample surface was distributed with less uniform porous structure. The absorption of material surface in the visible range of wavelength is higher than 90%, which can achieve good light trapping. The aspect ratio of modified silicon structure is 0.4. By simulating the geometric structure, theory proves that the structure is beneficial to achieve multiple reflections. Change the etching conditions and adopt the magnetic rotor, taking advantage of the stirring-accelerated effect to prepare black silicon material with hydrophobic capability. According to characterization and analysis by SEM and AFM, combined with theoretical models, the hydrophobicity of black silicon is considered ascribe to the roughness effect of modified surface. However, the significant change of roughness is caused by the dual micro-nano structures effect. The static contact angle of black silicon surface is measured 118°, which is adequate to achieve hydrophobic function.Although metal-assisted chemical etching method is low-cost, simple and easy to control, considering near-infrared absorption, the chemical way is described as useless. Even if the reflectance in the near-infrared range of wavelength reduces, the higher transmission leads to the lower absorption, and the value is close to zero.The method of femtosecond-laser microstructured silicon solves the problem timely. Due to the high laser-pulse energy, the silicon surface instantaneously melts and sulfur incorporate into the surface. The introduction of impurities leads to the impurity level in the silicon band-gap, and make the below-band gap wavelengths absorbed, thus achieving the 90% absorption of microstructured silicon from the near-ultraviolet to the near-infrared. In addition, the modified silicon surface is filled with a quasi-ordered array of micro-conical structures, and this structure has a high aspect ratio, which plays an importance role in the manifold repetition of light reflectance.The wet-etched black silicon is used to create silicon-based MSM photodiode, of which the modified surface is evaporated the electrostatic comb fingers and the other is covered with coplanar electrodes. The I-V characteristic curve of tested MSM photodiode is analysed, and it has turned out that the performance of device is stable, also with the good repetition. The femtosecond-laser microstructured silicon is used to fabricate the N+/N silicon-based photodiode that has higher dark current. The phenomenon is mainly caused by the surface defects of modified silicon. As known to all, the more surface defects exist, the more electron-hole pairs of recombination centers will form, both of this will give rise to the difficulty of carries transition.