Study Of Preparation And Photoelectric Detection Of Wide Spectral Response And Micro-nano Structure Silicon

Due to its special surface morphology and good broad-spectrum optical absorption,hyperdoped silicon has attracted widespread concern and deep research both at home and abroad. Currently, this new material can be used for silicon-based photodetectors,solar cells and other fields of optoelectonic materials.Laser has been used for modification and processing of materials for many years.Due to the particularity of the laser, the material after the modification can often show different performance. The hyperdoped silicon coverd with cone-shaped structure was fabricated by femtosecond laser scanning in SF6 atmosphere. The studies have shown that the height of conical microstructures on the surface is about several microns high or even higher, the absorption of material surface at both visible and near infrared range of wavelength is higher than 90%, which fully shows the characteristics of its high absorption and wide spectral response. High absorption of visible light is caused by light trapping formed by the unique cone-shaped structure. Due to the high energy of pulsed laser, silicon’s surface instantaneously melts and sulfur incorporated into the surface, the doping concentration is much greater than the solid solubility of S element in silicon. The introduction of impurities leads to the impurity level in the silicon band-gap, and makes the light of below-band gap wavelengths be absorbed, so as to realize the high absorption of the light at near infrared wavelengths.Hyperdoped silicon fabricated in SF6 atmosphere has a higher absorption, but the microstructures are not conducive to the followed preparation of devices, so that the material with special performance is not fully applied.The application of ion implantation solves this problem. Doping high concentrations of impurities in the surface of silicon by ion implantation, and using laser with low energy and low pulse number to irradiate, we can get the heavily doped silicon with surface roughness in nm level. The absorption at visible wavelengths still can reach more than 90%, and at near infrared wavelengths declines to 60%, but it is still much higher than the absorbtion of single-crystal silicon.The material’s carrier concentration, electrical resistivity and electron mobility were characterized by hall effect which exhibits different electrical properties compared with monocrystalline silicon. The carrier concentration can reach 1020cm-3, theresistivity is very low either, the electron mobility decreased to 82cm2v-1s-1. These are due to the high doped concentration.The PN/PIN photodetectors were made by hyperdoped silicon, and light-dark current and response curves were analysised. The maximum responsivity of PN-based device is 0.9 A/W. The response of devices commonly used on military can reach 0.17A/W. The maximum responsivity of PIN-based photodetector is up to 5.94 A/W, which fully shows the great potential of hyperdoped silicon in the field of photoelectric detector. But the two devices have high dark currents. This phenomenon is mainly caused by the surface defects of modified silicon and deep-level impurities of high doping. As known to all, the more surface defects exist, the more recombination of electron-hole pairs will form, both of them will arouse the difficulty of carries’ transition.