Research On Fabrication And Optoelectronic Properties Of Se-doped Silicon Using Femtosecond Laser Pulses

Silicon is widely used in semiconductor industry because of its abundant resource,resistant to high temperature and compatibility with the present integrated circuit.However,the response wavelength of silicon is less than 1100 nm due to its band-gap energy of 1.12 eV,thus limiting its applications in the near-infrared field.Chalcogen-supersaturated silicon gains a breakthrough on this issue.Chalcogen-doped silicon exhibits high absorption in wide spectrum from visible to near-infrared wavelength.Therefore,Chalcogen-doped silicon has great potential in applications of photo-detector and photocells.In this paper,Se-doped silicon is prepared by femtosecond-laser irradiation of Si coated with Si/Se bilayer films.The effects of number of pulses and Se film thickness on morphology,optical and electrical properties of Se-doped silicon are systematically investigated.The n+-n photodiode is prepared using Se-doped silicon,the dark current and photoresponse are measured and analyzed.The results show that the absorption of Se-doped silicon is over 90% from 400 to 2200 nm wavelength.The increase of absorptance in 400?1100 nm relates to the multiple reflections,and the improvement on absoprtance at wavelength from 1100?2200nm due to the surface morphology,lattice damage and dopant incorporation.The size of micro-structures,absorptance and sheet carrier density of Se-doped silicon all increase with increasing the number of pulses.On the contrary,the hall mobility decreases with the increase of pulse number.The responsivity of photodiodes also increases with increasing number of pulses from 50 to 250,the photodiode prepared with 250 pulses show the highest responsivity,achieves 0.889 A/W at 1064 nm.When the pulse number further increases to 500,the responsivity is decreased.The photoresponse is influenced by absorptance and surface morphology.The increase of pulse number is benefit for the absorptance,but it reduces the hall mobility as well.A large number of photo-induced carriers fail to cross the contacts and do not contribute to the generation of photocurrent,thus the photoresponse is reduced.Based on the above research results,the effect of Se film thickness on Se-doped silicon and its photodiode is studied with fixed 250 pulses.The study finds that the size of surface structure,absorptance and sheet carrier density of Se-doped silicon increase with increasing Se film thickness.However,the hall mobility has a downward trend along with the increase of film thickness.The photoresponse of photodiode at 1064 nm increases with increasing Se film thickness,the photodiode prepared with 125 nm Se film shows the highest responsivity.In summary,the experiments are designed to investigate the effects of pulse number and Se film thickness on optoelectronic characteristics of Se-doped silicon and photodiode prepared from this kind of material.The morphology,optical and electrical properties are analyzed to optimize the parameters to improve the photoresponse of photodiode.The photodiode prepared with 250 pulses,125 nm Se film acquires the optimum responsivity.the responsivity reaches 1.22 A/W at 1064 nm.