Study On Fluorescence Emission Of Silicon Induced By Nanosecond Pulse Laser

With the finding of fluorescence emission of porous silicon at room temperature, the research on luminescent structure and device based on silicon has become the focus and has drawn a lot of interest in its optoelectronics application. Electrochemical eroding and photochemical eroding are the traditional processing methods for preparation of porous silicon. When the sample was treated by anodic oxidation, some kind of etchant solutions was needed to form microstructures on the surface. Those preparation methods are complex and depend on etchant solutions. Not only were the solutions bad for health and environment, but also lead to low efficient and uncontrollable preparation. And they are also not suitable for industrial promotion and preparation with high quality and efficiency. Pulse laser micro-fabrication on silicon which caused the change of its optical property made it possible to prepare the sample by pulsed laser micro-processing technology.Based on the ultraviolet (UV) nanosecond pulsed laser micromachining system in the dissertation, we did experimental study of monocrystal silicon micro-fabrication and its fluorescence emission. The mechanism of the fluorescence phenomenon and the character of the radiation light were analyzed. It can be much easier to control the process of the preparation than traditional methods, and become independent of etchant solutions.The main achievements in the dissertation were listed as follows:1. Analysis of fabrication mechanism and fluorescence emission The process of fabrication of nanosecond pulse laser and monocrystal silicon was issued by the analysis of interaction and fabrication model. The physical explanation of fluorescence phenomenon and the mechanism of fluorescence emission of porous silicon were shown in the paper. Preparation of stable fluorescent microstructure based on silicon can be realized by nanosecond pulse laser micromachining technology. By analyzing of pulse laser fabrication factors, reference was supplied for the design of UV nanosecond pulse laser micromachining system.2. Design of UV nanosecond pulse laser micromachining systemThe laser micromachining system in the dissertation consists of 355nm wavelength nanosecond pulsed laser, optical and mechanical structures, a graphics preprocessing PC software and a control system based on DSP (digital signal processing chip) and FPGA (field programmable gate array chip), and some other auxiliary systems. The laser pulse width is less than 40ns, and the pulse repetition frequency can be adjusted from 1Hz to 100 kHz. A 3-dimensional work platform was driven by step motor with 32 subdivision technology, and single-step movement accuracy can be controlled in 625nm. The efficiency of laser fabrication can be ensured by high average power and pulse repetition frequency of the laser, and micro-fabrication can be realized by the cooperation of control system and work platform.3. Study on fluorescence emission of monocrystal silicon fabricatedThe analysis of fabrication and fluorescence emission of monocrystal silicon was realized based on the nanosecond pulse laser micromachining system. With SEM and other equipments, the surface structure and cross-section of fabricated slot was imaged. The internal part of silicon crystal was destroyed by the high power laser pulse. And the property of the material was also changed in the fabricated area. The explanation of fluorescence emission was illustrated and the character of spectrum was analyzed. The decay of the light intensity indicated that pulse laser micromachining technology can be used in preparation of silicon microstructure with stable optical property. And the dissertation provides a theoretical basis and experimental support for the future research of fluorescence emission of monocrystal silicon with the nanosecond pulse laser micromachining.