Fabrication And Investigation Of Black Silicon Of Enhanced Near-infrared Absorption

Silicon photonics have already widely applied in microelectronics andtelecommunications fields because this technique can implement various opticalfunctionalities in silicon and offer large-scale integration of multiple optical andelectronic functions on a single silicon chip. Photodetectors are the critical devices forsilicon optoelectronic integration. Silicon-based photodetector for wavelength below1100nm that corresponds to the band-to-band absorption have been commercialized.However, for the realization of IR detection beyond the wavelength of1100nm,silicon was not considered the right material because of its low absorptivity.Femtosecond laser microstructured silicon can expand the absorption wavelength ofsilicon to2500nm in NIR. However, the absorption of femtosecond lasermicrostructured silicon in NIR region (from1100nm to2500nm) extremely reducedby annealing process that a necessary step for the converting of amorphousmicrostructured surface silicon to crystalline silicon. Furthermore, for the higherannealing temperature, the decreasing degree of NIR absorption of black silicon ismore remarkable. Therefore, the high NIR absorption of femtosecond lasermicrostructured silicon disappear after being photodetector.The main reason for the poor NIR absorption of femtosecond lasermicrostructured silicon after annealing is the unbalanced S impurity diffusing intograin boundary, which cannot make a contribution to IR absorption, in hightemperature. The idea of this paper is to be co-doped by introducing two kinds ofimpurity atoms into silicon, so that the sulfur atoms would be prevented fromdiffusing into the grain boundary. The details of the method are to fabricate the blacksilicon in the different kinds and different ratio of the mixed atmosphere byfemtosecond laser. A series of S-N co-doped microstructured black silicon byfemtosecond laser is fabricated in mixed atmosphere of N2and SF6. Compare with thes-doped black silicon a novel property is that the high below bandgap IR absorbance of black silicon can be held after annealing very well. In the end, the IR black siliconphotodetector is produced based on this excellent IR absorbance performance afterannealing in order to test the IR detecting capability of the co-doped black silicon anda high photoresponse with58mA/W was obtained for1310nm detecting light.