| In the past 70 years,silicon-based integrated circuit technology has made outstanding contributions to the development of science and technology.In the past three decades,silicon-based optoelectronic technology has been systematically and deeply developed,and has the advantages of high integration,small size,and strong compatibility with microelectronic processes,playing an important role in many fields such as sensing,imaging and artificial intelligence.In the current field of silicon-based photonics,silicon-based infrared photodetectors,as an important part of silicon-based optoelectronic integrated circuit(OEIC)chips,are very important to work in the communication optical band(such as 1310 nm and 1550 nm two optical communication windows).However,due to the limitation of band gap of monocrystalline silicon(1.12 e V at room temperature),infrared light with wavelength greater than 1100 nm is transparent,so monocrystalline silicon photodetectors cannot be used in infrared photoelectric detection.Until the end of the last century,the emergence of microstructured silicon(black silicon)obtained by irradiating the surface of monocrystalline silicon using femtosecond pulse laser in Sulfur hexafluoride(SF6)atmosphere made infrared detection of crystalline silicon materials possible.It was found that the main reason for the enhanced absorption of this black silicon material in the near-infrared band(λ>1100 nm)was the hyperdoped of sulfur(S).Because S doped into silicon can introduce deep energy levels in its bandgap,and when the doping concentration of S is high(>1019 cm-3),the introduced deep energy level can expand to form an impurity band(intermediate band)in the forbidden band of silicon,with the help of the transition of the impurity band,S-hyperdoped black silicon realizes the absorption of photons with energy less than the silicon band gap.Therefore,the introduction of intermediate band(IB)into the forbidden band of silicon by supersaturated doping of deep energy level impurities provides a possibility for infrared detection of silicon as an effective method that can broaden the absorption edge of single crystal silicon.However,at present,there are still the following two main problems in hyperdoped black silicon infrared photodetectors:(1)The problem of poor infrared absorption thermal stability of black silicon materials.The absorption of S-hyperdoped black silicon materials in the infrared band was unstable,and the absorptance was greatly reduced after thermal annealing.(2)The problem of low photoelectric conversion efficiency of black silicon photodetectors.On the one hand,the high concentration of ionized impurities in the doped layer of black silicon can hinder the transport of carriers.On the other hand,the lateral distribution continuity of impurities in the doped layer is poor,which makes the junction region formed between the black silicon layer and the Si substrate discontinuous.In this paper,firstly,in order to solve the poor infrared absorption thermal stability of S-hyperdoped black silicon,it is proposed that the transition metal chromium(Cr)is used as dopant to prepare Cr-hyperdoped black silicon materials with infrared absorption heat stability and black silicon infrared photodetectors.Secondly,to solve the scattering problem of ionizing impurities introduced by conventional element hyperdoped,an innovative idea of using the inert element argon(Ar)as dopant is proposed.In addition,in view of the poor transverse distribution continuity of black silicon doped layer,Ar-hyperdoped silicon materials and infrared photodetectors were fabricated by ion implantation followed by pulsed laser irradiation.Finally,in order to further improve the infrared absorptance of the Ar-hyperdoped Si and the potential barrier between the Ar-hyperdoped Si layer and the substrate,the supersaturated Ar/S co-doped silicon material and infrared photodetectors were prepared by ion implantation followed by pulse laser irradiation.Through the above research,the photoelectric conversion efficiency of the black silicon infrared photodetector has been significantly improved.The main research contents are as follows:(1)Study on Cr-hyperdoped black silicon and infrared photodetector.The Cr-hyperdoped black silicon was prepared by femtosecond pulsed laser irradiation,and the doping concentration of Cr atoms in the black silicon layer can exceed 1020cm-3.The electrical property measured determined that the deep donor energy level introduced by Cr in the forbidden band of silicon is at 0.39 e V below the bottom of the conduction band,and the carrier concentration due to ionization of Cr impurities is about 1015 cm-3 at room temperature.Based on the carrier concentration difference established between the Cr-hyperdoped layer and the Si substrate,and the thermal stability of the material(absorptance ~55%@1310 nm)characteristics,the Schottky junction/N+-N junction double-junction black silicon infrared photodiode was prepared,in which the N+-N junction could respond to 1310 nm near-infrared light at4.3 V reverse bias voltage and the responsivity of 1310 nm near-infrared light can reach 0.57 A/W.Combined with the band diagram and switching characteristics of the device,the optical response gain and infrared detection mechanism of Cr-hyperdoped black silicon photodetectors were discussed.(2)Study on Ar-hyperdoped silicon and infrared photodetector.For the first time,we selected the inert element Ar as the doping source,and the Ar-hyperdoped silicon material was prepared by ion implantation followed by pulse laser annealing technology.After ion implantation,the peak concentration of Ar atoms in the hyperdoped layer can reach 1020 cm-3(the first hyperdoping).Different from the traditional nanosecond pulsed laser annealing after ion implantation,the femtosecond pulsed laser irradiation used in this paper can not only improve the crystallization quality of the ion implantation layer as a post-annealing process,but also can realize the secondary hyperdoped of the inert element Ar,and the doping concentration of Ar caused by laser irradiation can reach 1021 cm-3.There are two peak concentrations of Ar atom distribution in the doping layer,that is,the dual-zone hyperdoped of Ar is realized.The ionization energy of the defect energy level related to Ar is 0.371 e V,which is the deep donor energy level,so hyperdoping of Ar can form an intermediate band in the bandgap of silicon,and the absorptance of 1310 nm near-infrared light is measured to be 18.7%.In addition,the carrier concentration of the Ar-hyperdoped layer is about 1014 cm-3,and the carrier concentration difference established between it and the Si substrate is conducive to the formation of N+-N junction.The prepared Ar-hyperdoped silicon double-junction photodiode has a responsivity of 0.975 A/W and 1.28 A/W for 1310 nm and 1550 nm near-infrared light under the reverse bias voltage of 12 V,respectively,breaking the record of responsivity of bulk hyperdoped silicon detector at low bias.Combined with the band diagram analysis,because the Schottky junction and the N+-N junction share the Ar-hyperdoped layer,when the reverse bias voltage of the Schottky junction exceeds a certain value,the double junction has a reach-through breakdown,and the decrease in the height of the N+-N junction barrier will lead to a larger hole/electron injection ratio,therefore,the photodetector exhibits high optical response and photoconductivity gain characteristics at room temperature.(3)Study on supersaturated Ar/S co-doped silicon and infrared photodetector.Ar-hyperdoped silicon materials were prepared by ion implantation,and on this basis,supersaturated S impurities were doped to the silicon by femtosecond pulse laser irradiation to achieve the co-doping of supersaturated Ar and S,in which the doping concentration of S atoms could exceed 1019 cm-3.In addition,femtosecond pulsed laser irradiation also plays a role in annealing the ion implantation damage layer while achieving supersaturated S doping,and the crystallization quality of the ion implantation layer after pulsed laser irradiation is significantly improved.Compared with single-element Ar-hyperdoped silicon,the introduction of S impurities has the following advantages:(i)improve the infrared absorptance of the hyperdoped layer,and the absorptance of 1310 nm near-infrared light is 32%;(ii)increase the carrier concentration of hyperdoped layer,the bulk carrier concentration of hyperdoped layer is about 1017 cm-3 at room temperature.Therefore,supersaturated Ar/S co-doped can increase the barrier height of the N+-N junction,thereby improving the photodetector’s ability to separate photogenerated carriers,and ultimately improving device performance.Based on the large carrier concentration difference between the hyperdoped layer and the silicon substrate,supersaturated Ar/S co-doped silicon photodetectors were prepared for the first time by ion implantation followed by pulsed laser irradiation double doping technology,and the N+-N junction has good rectification characteristics.At the reverse bias of 9 V,the responsivity of this optimized device can reach 222 m A/W at 1310 nm.In order to reduce the noise of the device and further improve the photoconversion efficiency of the photodetector,the passivation process was used to reduce the dark current of the detector.After passivation,the dark current of the detector can be reduced by an order of magnitude,and the specific detectivity of the detector significantly improved.In summary,the ultimate goal of my work is to realize the infrared detection of silicon detectors,and three hyperdoped black silicon materials were prepared by non-equilibrium doping technology,extending the absorption edge of silicon to the near-infrared band of 2500 nm.In this paper,we made a profound study in the properties of hyperdoped silicon materials and device,and the performance of hyperdoped silicon materials was regulated by changing the laser parameters and annealing process,and the optimized hyperdoped silicon photodetectors realized the high-response detection of near-infrared light in the two communication windows of1310 nm and 1550 nm.The results of this paper show that hyperdoped black silicon materials have broad potential application value in the field of infrared detection. |
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