Study On Supersaturated Doped Black Silicon With Transition Metal By Femtosecond Laser

In the field of optoelectronics,semiconductor silicon hold dominant position.This is due to the lower cost of silicon and the better compatibility of modern standard COMS processes;however,due to the bandgap limitation,the infrared absorption of silicon will be very lower above 1.1?m.Therefore,silicon materials are not suitable for application in the infrared detection field.The infrared absorptance of the supersaturated sulfur-doped black silicon material prepared by the femtosecond laser irradiation can be more higher 90%,The high infrared absorptance of the black silicon material provides strong support for the infrared detection of the silicon material;but the sulfur doped black silicon material has a poor thermostable infrared absorption after thermal annealing;at the same time,the supersaturated doped sulfur impurity will introduce a high free carrier concentration to make the device have a large background noise;The thermal annealing process is a necessary process for preparing the device.Therefore,it is still difficult to prepare a black silicon detector with high responsivity.The transition metal element gold has a compensating effect between donor and acceptor impurity levels in the silicon bandgap,which can reduce its free carrier concentration,thereby reducing the dark current of the device and improving the device response.Therefore,we prepared a supersaturated gold-doped black silicon material by femtosecond laser irradiation method.It is hoped that a black silicon material with a lower carrier concentration and better thermal stability can be prepared.This study found that the absorptance of supersaturated gold-doped black silicon in the 0.25?m-2.5?m band after the femtosecond laser irradiation is higher than that of the single crystal silicon substrate.The infrared absorptance of the supersaturated doped black silicon material is higher than 50%in the 1.1?m-1.8?m band,and the infrared absorptance shows a decreasing trend with the increase of the laser power and it has a good thermal stability;the increase of the infrared absorptance is caused by the introduced structure defect state and the sub-band absorption of deep gold impurity level transitions.In addition,when the doped depth of the gold-doped black silicon layer is 100nm-250nm,the gold impurity concentration can reach higher 10¹⁹ cm^-3,and it has a very low surface free carrier concentration is 10¹⁰ cm^-2-10¹11 cm^-22 result from self-compensation between gold impurity levels.In the same time,a gold-silicon alloy phase forms on the surface of the gold-doped black silicon layer.We analyzed the temperature-dependent Hall Effect and found that the gold impurity ionization energy is 612 meV in the black silicon layer;we can also find that the sign of Hall coefficient sign in the gold doped black silicon layer is the result of the laser power parameter and the Hall test temperature.When we continuous increase of the Hall test temperature,a positive sign to negative sign transition of the Hall coefficient indicates that the gold impurity plays a major role as the acceptor impurity level in the black silicon layer.Finally,we found that the gold-doped black silicon device has a responsivity of up to4.6 mA/W for 1310 nm wavelength light when the reverse bias is-10V.