Non-equlibrium Silver Doping Of Crystalline Silicon And Its Photodetector

Silicon-based optoelectronic technology has the advantages of high speed,low cost,low loss and high integration.Driven by the national strategy and market demand,it is facing the historical opportunity of large-scale industrialization and marketization,and reprensents one of the most promising technology field in the era.However,due to the limitation of indirect band gap of 1.12 eV,silicon is not traditionally considered as a suitable candidate for photodetectors operating at the wavelengths beyond 1100 nm,which severely restricts its application in photonics.In recent years,a new method,which calls femtosecond laser hyperdoping of silicon,has become a topic of rapidly increasing interest in fabricating high-performance all-silicon photodetectors,especially for the near-infrared applications.However,the responsivity is still too weak for practical short-wavelength infrared photodector applications,which needs a more careful and systematic research.This thesis focuses on the preparation and properties of silver hyperdoped silicon(Si:Ag)samples,as well as its applications in photodetectors.The innovative results achieved in this thesis are addressed as following:(1)We have successfully prepared the silver hyperdoped silicon samples by the method consisting of ion implantation and femtosecond laser melting(fs-PLM).The peak concentration of silver dopant approaches b02V cm-3,more than five orders of magnitude above the equilibrium solid-solubility limit.Compared with the conventional silicon,the optical absorptance of Si:Ag samples is greatly enhanced in the wavelength range of 300-1800 nm.It is resultant from the combination of surface texturization induced anti-reflection and sub-bandgap photon excitation assisted by dopant levels(Ec-0.285 eV).Moreover,the extended infrared absorptance can be greatly deactivated by a post-annealing.It is verified that the deactivation is not caused by the long-range diffusion of supersaturated silver dopants.(2)We have succeeded in fabricating a highly sensitive and room-temperature operated bulk silicon photodetector based on silver hyperdoped silicon.The detector exhibits a diode-rectifying characteristic in the dark and a photoconduction characteristic under illumination.At-3 V,the responsivity can approach 8.56 A W-1,which stands on the same positions as one of the highest EQE values in the hyperdoped silicon devices previously reported.Based on our experimental results,we for the first time put forward the mechanism for the photoresponse gain,which is attributed to the enhancement of hole injection resulting from the electron traps with the energy level of Ec-0.28 eV induced by substitutional silver atoms in the Si:Ag layer.Moreover,the photodetector exhibits a high detectivity,a rapid response speed and a large linear dynamic range.(3)We have investigated the short-wavelength infrared(SWIR)detection performance based with the Si:Ag which is prepared by a high-fluence femtosecond laser melting.We creatively introduce a large density of surface defects in the hyperdoped layer to creat a strong surface recombination,which can quench the charge collection for short-wavelength excitation and lead to a visible-blind but SWIR-sensitive characteristic.The bulk electron traps induced band-bending and two-stage carrier excitation cause the enhanced sub-bandgap photoresponse.The photoresponse of the Si:Ag photodetector can be extended to the wavelength of 1600 nm,and the room-temperature responsivity of 504 mA W-1 at 1310 ne and 65 mA W-1 at 1550 nm can be obtained.These values,to our knowledge,represent the highest response level in the previously reported hyperdoped silicon photodetectors.(4)We have fabricated the Si:Ag/Gr hybrid SWIR photoconductor,where the graphene is used as an electron transport layer.Our experimental results have proven that the graphene can improve the latetal transport ability for electrons.The external quantum efferciency of the detector can approach 97.26%and 7.37%for the wavelength of 1310 nm and 1550 nm,respectively.By dispensing Pt nanoparticles to induce the Localized Surface Plasmon Resonance(LSPR)and scattering effect,the sub-bandgap absorption and optoelectronic performance can be further enhanced.