| Silicon is the foundation material of integrated circuits,and has become one of the important materials of the modern information industry.Whether the development and replacement of transistors and computers,and even the development of communication networks,it is closely related to silicon single crystals,and its quality and size are also constantly improving.The development of silicon single crystals has reached the edge of Moore’s Law.Based on silicon-based modulation,silicon-based electronic products have penetrated into various disciplines and fields.In the 1980s,Soref et al.first proposed the concept of silicon photonics,the core of which is to integrate silicon optics into optical chips to form photonic processing information function devices.At the same time,the research and development of silicon-based photonics devices can realize the seamless connection between silicon-based photonics and silicon-based electronics through the advancement and development of silicon-based electronics,and develop large-scale integration technologies.The forbidden band width of silicon is 1.12 eV and the indirect band gap determines that the response band locates only in the wavelength range less than 1.1μm.At the same time,the silicon material has a centrally symmetrical structure,which determines that it cannot achieve electrical modulation by linear electro-optical effect,undoubtedly limiting the progress and development of silicon-based photonics.The basis of photonics is light source,modulation device and detector.Based on stimulated Raman scattering,band modulation and semiconductor growth technology of various silicon-based substrates,silicon-based light sources are more developed,while silicon-based light modulators are mainly focusing on the active modulation of band-modulation.The mid-infrared band with longer communication band and longer wavelength is in the exploration stage,while the silicon-based detectors are relatively less studied,especially in the communication band and the mid and far infrared range.Following the development trend of silicon-based optoelectronics,this paper is concentrated in silicon-based modulation devices and detectors.This work employs the ion implantation method for injecting sulfur ions into silicon crystal,to introduce an impurity level into the original band gap of intrinsic silicon.Using this way can change the original energy band structure of silicon and expand the wavelength response range of silicon.This paper also tests and characterizes the optical properties of silicon after ion implantation focusing on its communication band and mid-infrared band;applies the prepared samples as passively optical switchers at 1.3 μm,1.4 μm and 2 μm and designs a wide-band silicon-based passively optical switcher from communication band to mid-infrared band.The pulse modulation at these three wavelength bands is realized,and the pulsed laser output is obtained.This paper also prepares the silicon-based photodetector and explores its photodetection performance from near infrared to 2 μm,which lays the foundation for its optoelectronics application.The specific contents are as follows:1.Preparation and characterization of the sulfur ion implanted single crystal silicon samplesAccording to the theory,the doping of chalcogens into silicon crystal can introduce an impurity level with a width to the original 1.12 eV bandgap of silicon.As increasing the doping concentration,the impurity level will be broadened and gradually close and fused to the conduction band.So that the silicon material will change from a semiconductor state to a metal state,and the forbidden band width determines the response wavelength of the semiconductor.Therefore,the doping concentration of the chalcogen element can modulate the energy level structure of the silicon,thereby adjusting the wavelength response range.The injection of sulfur ions into the silicon crystal employed the ion implantation method with an implantation energy of 95 keV and an implantation dose of(3,5,7,9)× 1015 cm-2,according to the expected doping concentration and the depth simulation calculations using SRIM software.By secondary ion mass spectrometry,the concentration distribution of different samples in the silicon wafer with depth was obtained,and the results were basically consistent with the expectation.The rocking curve of the high-resolution X-ray diffraction spectrum and the Raman spectrum show that as the implantation dose increases,the crystallinity of the silicon wafer sample decreases,which can possibly adjust its photoelectric properties.The transmission spectrum shows that the sample after sulfur ion implantation has absorption enhancement in two wavelength bands compared with the pure intrinsic silicon wafer:from 1.1 μm to 1.7 μm and 1.7 μm to 7 μm.According to its theoretical calculation,the absorption enhancement from 1.1 μm to 1.7 μm consists of the electron transitions from the valence band to the impurity level and from the impurity level to the conduction band.The absorption enhancement of 1.7 μm-7 μm mainly comes from the electronic transition from the impurity level to the conduction band.2.Nonlinear saturable absorption properties of the sulfur ion implanted silicon wafer samplesAs the wide-band optical switcher,the nonlinear absorption characteristics of the prepared sulfur ion implanted silicon wafer in the 1.55 μm communication band and the 2 μm mid-infrared band were studied by means of Z-scan method and power variation,respectively.The prepared sample has saturable absorption characteristics because the electrons possess fermion characteristics,so that they must follow the Pauli exclusion principle.At 1.55 μm,the nonlinear absorption coefficient β is-0834,and the saturable light intensity is 3.19 MW/cm-2.At 2 μm,the minimum saturable light intensity is 0.52 kW/cm-2,and the modulation depth is 8.16%.In addition,we find that the modulation depth and saturated light intensity increase with the increase of sulfur ion doping concentration,and the results show that the prepared silicon material has excellent saturable absorption performance,small saturable absorption intensity.It can work under a small light source,has low loss and generates less heat.All of these proves that it has the potential to be an excellent passive light modulation device.3.Study on the passively optical switching performance of the sulfur ion implanted silicon waferBased on the saturable absorption properties of the sulfur ion implanted silicon waf-er,the sample is applied to the all-solid-state laser as the passively optical switcher for optical modulation to generate the passively Q-switched pulsed laser.The passively Q-switched laser outputs with wavelengths of 1.34 μm,1.42 μm and 1.94μm were realized.The narrowest achieved pulse widths were 402 ns,167 ns and 144 ns,respectively.The highest repetition rates were 245.5 kHz,75.76 kHz and 88.60 kHz respectively.The obtained maximal pulse energy was 210 nJ,220 nJ,and 1825 nJ,respectively.It has verified that the optical switching performance of the sulfur ion implanted silicon wafer,and it can be used as a wide-band passive light modulation device from near-infrared to mid-infrared wavelengths.This paper provides a new material in ultra-fast pulse generation,and also inspires the fields of silicon-based optical signal processing communications for the future in the infrared band.4.Photodetection performance of the sulfur ion implanted silicon waferBased on the theory and experiment of the energy level structure,it is found that the response wavelength of the sulfur ion implanted silicon wafer can be extended to the infrared wavelength,and a wide-band silicon-based photodetector device may be prepared.On this basis,photodetector devices were fabricated and their photodetection properties at wavelengths of 1.34 μm,2 μm and 2.8 μm were studied.It was found that they have different photoelectric responses in different wavelengths.In the meantime,the photoelectric response of the device was asymmetrical under different bias voltage directions,and there was a negative photogenerated current at a specific bias voltage.This is may be related to the Schottky barrier asymmetry and thermoelectric effect at the electrode.The samples with middle doping concentrations have the best performances,which may be due to the reduction of carrier mobility caused by the lattice destruction on account of the implanted ion.The relevant mechanism needs further research.In summary,in order to expand the applications of the silicon crystal,the impurity level is introduced into the silicon band gap by ion implantation,and the response wavelength range of silicon is extended to mid-infrared.This paper has made the characterizations of linear and nonlinear optical properties and realized wide-band pulsed laser modulation and photodetection,implying the samples can be applied as optical switchers and photodetectors.The prepared devices may have potential applications in optical switching and photodetection. |
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