Fabrication And Photoelectric Properties Of Micro/nanostructured Silicon

Silicon is the most widely used semiconductor material.It is not only easy to be purified with high temperature resistance and low cost,but also an abundant natural resource.However,the band gap of monocrystalline silicon is only 1.124 eV?300 K?.And it can only absorb the visible light effectively,so it can not fully meet the requirement for optoelectronic detectors in near infrared.By micro/nano etching the surface of monocrystalline silicon which in means of physical or chemical methods,and doping with S,Te,Se etc.,a desired light trapping structure could be formed with a new changed energy band in silicon,so that it is sensitive to near infrared.Therefore it has become one of the hotspots and frontiers in the field of optoelectronics both at home and abroad in recent years.In order to study the surface morphology,spectral absorption and metal-semiconductor contact characteristics,three kinds of micro/nanostructured silicon materials were fabricated by femtosecond laser,MEMS technology and metal catalytic etching,respectively.The variation of minority carrier lifetime was investigated after the surfaces of micro/nanostructured silicon were passivated by Si N_x thin films.The main results are as follows:?1?In the range of 400 nm²000 nm,the spectral absorption of black silicon fabricated by femtosecond laser with different power,scanning speed and gas atmosphere is significantly higher than that of monocrystalline silicon.The black silicon could have the finest micro/nanostructure,the most complete cone form and the highest spectral absorption when the laser power is set at 200 mW,the speed 1mm/s and the atmosphere SF₆.The light absorptivity can be increased to 90%in near infrared.?2?In the visible wavelength,the spectral absorption of the microstructured silicon etched by MEMS method with different pattern period and etching depth is higher than that of monocrystalline silicon,but hardly improved in near infrared.In the case of D=4?m/T=6?m and 70 times etching,the microstructured silicon presents periodically arranged surface structure and higher spectral absorption.The light absorptivity can be increased to 70%at the range of 400 nm¹100 nm.?3?In the visible and near infrared wavelength,the spectral absorption of nanostructured silicon etched by metal catalytic corrosion with different etching methods and silver plating time is significantly higher than that of monocrystalline silicon.The etched silicon surface has finer nanostructure,better fiber form and higher spectral absorption when treated by 60 s silver plating.The light absorptivity is increased to more than 90%at the range of 400 nm¹100 nm,and 70%at the range of1100 nm²000 nm,respectively.?4?Micro/nanostructured silicon fabricated by femtosecond laser,MEMS technology and metal catalytic corrosion could form a good Ohmic contact with Ag/NiCr electrode.It is found that the contact resistance between micro/nanostructured silicon and Ag/NiCr electrode is relatively smaller than that between monocrystalline silicon and Ag/NiCr electrode,and the smallest contact resistance goes to the nanostructured silicon etched by metal catalytic corrosion.?5?The minority carrier lifetime of monocrystalline silicon is decreased after being etched by three different kinds of processes.The carrier recombination of the micro/nanostructured silicon can be reduced and the minority carrier life can be promoted when the etched surfaces are passivated by SiN_x thin film.