Study On Infrared And Terahertz Photodetection Based On Two-dimensional Materials

Terahertz technology has achieved rapid development in the fields of terahertz spectroscopy,high-speed communication,security imaging,biomedicine,astronomy and remote sensing with tremendous application potential.The research on terahertz detection technology is always the key of terahertz technology.The rapid development of semiconductor micro-nano processing technology provides a strong technical support for the research on terahertz and infrared optoelectronic devices with low dimensional materials.The semiconductors(semimetals)with two-dimensional layered structure exhibit unique electronic and optoelectronic properties due to their in-plane carrier transport channel,large surface area and subwavelength(deep subwavelength)thickness,which provide new opportunities for high-performance photo detection with high speed,high gain,polarization sensitivity and broadband response.However,limited by high dark current and weak photoelectric coupling,the performance of visible-infrared-terahertz detectors based on two-dimensional materials is still unsatisfactory.In particular,there is still much room to improve the performance of photodetectors in infrared-terahertz regime.Therefore,the research on photodetectors from visible,infrared to terahertz regime based on graphene,black phosphorus,topological semimetal and excitonic insulator is carried out.In this paper,the photo response mechanism of the detectors mentioned above is studied by numerical calculation,theoretical analysis and experimental test in detail.The performance of the detectors is improved by a variety of new mechanism and methods,such as metamaterial antenna coupling,ultrashort channel focusing,asymmetric contact electrode,van der Waals heterojunction and excitonic insulator phase transition.The main innovations in this paper include:(1)Based on the numerical calculation and theoretical analysis,graphene based terahertz detectors with metamaterial micro-nano structure antennas are designed and fabricated.The terahertz detectors with high responsivity and high-speed are realized by new mechanism of antenna coupling and electrical regulation.The Finite Difference Time Domain(FDTD)method is used to study the effects of Square-spiral antenna and Split-Ring Resonator antenna in terahertz coupling and focusing process.The polarity reversal of the photocurrent in the source-drain voltage and gate voltage sweep is analyzed.The contribution of photoconductivity,photo-thermoelectric effect,bolometric effect and plasma wave resonance effect to photocurrent is clarified.These terahertz detectors have the advantages of simple preparation process,compatibility with silicon based semiconductor technology,easy to control,mass production and so on,which performance is in the forefront of similar devices.(2)In order to achieve terahertz detectors with high speed and high sensitivity at room temperature,ultrashort channel devices are designed and fabricated.By improving the traditional device preparation technology,the ultrashort channel devices beyond skin-depth limit are realized by low-cost obliquity deposition technology,improving the application capacity of two-dimensional material devices in terahertz regime.The detectors overcome two difficulties in the terahertz detection driven by photo-thermoelectric effect with two-dimensional materials:the mismatch between the large spot and the small heat sensitive region and the mismatch between the small material thickness and the large terahertz wavelength.In this work,terahertz electromagnetic field can be focused in the sub-30 nanometer scale.The asymmetric contact potential is used to promote the high efficient generation and photoelectric conversion of hot carries in the black phosphorus channel under terahertz excitation,thus realizing high sensitive terahertz detector and transmission imaging at room temperature.(3)As a new type of transition metal chalcogenides(TMDs),Platinum Selenide has unique advantages in long wave detection,such as broadband and fast response speed,which provides a new opportunity for the research on terahertz detector.In this paper,the devices based on type II Dirac semimetal Pt Se₂ are designed and fabricated to achieve high-speed,high response terahertz detection at room temperature.In order to overcome the disadvantages of high dark current and high noise when the detectors work at biased voltage,the methods of introducing asymmetric contact or constructing van der Waals junction are used to realize the operation at zero biased voltage,which can suppress the dark current and noise and improve the sensitivity of terahertz detection,realizing non-destructive transition imaging at room temperature.(4)The excitonic insulator Ta₂Ni Se₅ has robust direct band gap characteristics and high absorption ability in the visible-infrared regime,which provide favorable conditions for visible-infrared photo detection.In this paper,we have grown and characterized high quality Ta₂Ni Se₅ materials,fabricated a broadband photo detectors and measured their performances.It is found that the detectors are sensitive not only in visible-infrared regime,but also in terahertz regime.The response speed in terahertz regime is improved by three orders of magnitude than in visible-infrared regime,which confirms different response mechanism.In addition,the existence of excitonic insulator phase is proved by polarization Raman spectroscopy,X-ray diffraction and transmission electron microscopy.The photocurrent will also change significantly with1550 nm laser irradiation around the temperature of excitonic insulator-semimetal phase transition.This work may provide a new method to explore excitonic insulator phase transition by light excitation.