Research On Bandgap Modulation Of Hyperdoped Silicon And Application Of Near Infrared Photodetector Controlled By Ion Implantation

Traditional silicon-based devices couldn't show desirable near-infrared(NIR)photoresponse due to limitation of optical bandgap(1.12 eV)of silicon,so much effort has been focused on enhancing the magnitude of silicon's photoresponse at NIR wavelengths recent years.The discovery of chalcogen-supersaturated silicon fabricated by femtosecond-laser pulse irradiation in SF6 atmosphere demonstrated an approach to enhance the sub-bandgap absorption.This kind of silicon showed an absorptance of over 90% both at visible and NIR wavelengths.The unique property gained extensive attention and deep research rapidly.At present,this new type of silicon material has already been used in silicon-based photodetectors and photovoltaic devices.It will surely bring a revolution of silicon-based device.Under the irradiation of high-energy fs-laser pulses,a rapid melting and resolidification process occurs in which sulfur elements incorporate into the surface of the material,and the impurity concentration can exceed the solid solubility of sulfur in silicon.The impurities introduce an impurity-band in the band gap of silicon,so that the photon with energy less than the band gap can be absorbed,realizing the absorption of light in the near infrared band.In addition,laser ablation reconstructs silicon surface and generates a series of cone arrays.When light is irradiated onto the surface of the material,it is reflected several times in the cones,then the absorptance is significantly improved.This new silicon material fully shows the characteristics of high absorption and broad spectrum.Although hyperdoped silicon prepared by fs-laser in SF6 atmosphere shows a high absorptance both at visible and near infrared wavelengths,it is not conductive to the fabrication of devices due to the high cone arrays on the surface.Ion-implantation assisted by fs-laser ablation process solves this problem: incorporating sulfur impurities into silicon surface by ion-implantation,and then using fs-laser with low energy and number of pulses to scan wafers.During this process,the electrical characteristics of the impurities can be activated and the height of cones is on nanometer order.The absorptance of the as-prepared silicon can still reach 90% at visible wavelength,and the absorptance at near infrared wavelength is less than that in the SF6 atmosphere,but it is still up to 60%.By comparing the absorptance of hyperdoped silicon prepared with different ion implantation concentrations,the relationship between absorptance and doping concentration was analyzed.Carrier concentration and carrier mobility were characterized by Hall measurement.The material exhibited different electrical properties compared with monocrystalline silicon.Under the highest doping concentration,sheet carrier density was up to 1015 cm-2,but carrier mobility decreased to 77cm2v-1s-1.These unique electrical properties are caused by high doping concentration.Hyperdoped silicon was made into N+/P photodetector to measure its dark current and responsivity curves.Although the absorptance decreased with dopant concentration,the device still had a higher response due to its higher carrier mobility.Ion implantation bonded with femtosecond laser process provides a new method for preparing low-cost,broad-spectrum silicon-based detectors.The new type of hyperdoped silicon performs its tremendous potential in silicon-based device field.