Research On Infrared And Terahertz Detectors Based On Novel Nanomaterials

Terahertz wave occupies a unique position in the electromagnetic spectrum,and its frequency is between microwave and infrared bands with the characteristics of low photon energy,strong penetration,and large transmission capacity,which has great application prospect and value in information communication,biomedicine,quantum computing,national defense security,and deep space exploration.As the core of terahertz technology,terahertz detection can transform terahertz optical information into readable electrical information.The traditional Schottky terahertz detector is difficult to integration.Commercially popular Gorey and other thermal terahertz detectors are slow response time with internal thermal noise.The superconducting detectors in aerospace applications work on ultra-low temperature,greatly increasing the cost and volume of detector use and other status.The current research on new materials represented by graphene by virtue of layerlike van der Waals force,high carrier mobility and high stability.The performance of new terahertz detector based on the materials can improve the above problems to a certain extent,but also face many scientific challenges:extremely low light absorption rate,slow response time,weak optical coupling ability of the antenna structure,etc.These limit its further development.In this thesis,we explore new nanomaterial systems and introduce topological effects into terahertz photodetection to improve the sensitivity of the detector through an effective charge separation mechanism,and we design asymmetric device structures and prepare heterojunction terahertz detectors with the help of weak interlayer van der Waals forces of nanomaterials to further suppress dark currents and improve the sensitivity of the photodetector.Thus,we studied the terahertz detectors based on new two-dimensional nanomaterials such as nickel telluride,zirconium germanium selenium and their heterojunctions.In order to enhance the practical applications of the detectors,we further carried out experiments on the broadband response based on black arsenic and its heterojunction detectors,and the detection bands covered visible,near-infrared and terahertz frequencies.The whole research approach includes new nanomaterial growth,terahertz detector structure design and simulation,detector process preparation,room temperature optoelectronic performance characterization and mechanism analysis,and room temperature terahertz active imaging applications.The research of this thesis is as follows:1.The high performance terahertz detectors based on topological materials nickel telluride(NiTe2),are explored.This material has exotic optoelectronic properties including high photon absorption,nonlinear effects and enhanced displacement currents,which provide a novel research platform for low-power and highly sensitive at low photon energies.Therefore,we first grew the nickel telluride crystal material by the melting method,used first-principles calculations and angleresolved photoelectron spectroscopy experiments to verify the characteristics of type II Dirac semimetals,and designed a sub-wavelength period logarithmic terahertz receiving antenna.By the micro-Nano processing technology,a metal-nickel telluride-metal structure of the terahertz detector was prepared,and the room temperature terahertz detection performance and imaging application were characterized.Experiments show that in the intrabank process of terahertz detection,the excited chiral electrons undergo asymmetric skew scattering in the inversion symmetry-broken surface state to generate a net photocurrent,which realizes the high-efficiency photoelectric conversion capability of terahertz.In the self-driving mode of the detector at room temperature,the terahertz responsivity reaches 0.25 A W-1,the response time reaches 1.6?s,and the noise equivalent power is lower than 89 pW Hz-1/2(the performance level of the current commercial GaAs terahertz unit detector:the responsivity of 1 mA W-1 and the Noise equivalent power of 1 nW Hz-1/2),which verified the high stability of the unit device and the application capability of terahertz imaging at room temperature,and confirmed that this type of material system is capable of detecting lowenergy terahertz photons.2.With the excellent thermoelectric properties of topological materials,two terahertz detectors with asymmetric structures were designed from the perspective of device structure and energy band engineering,and the terahertz detectors with asymmetric source-drain metal structures were prepared to realize the conversion of low photon energy signals to electrical signals from the perspective of device structure and energy band engineering.In this work,a new type of zirconium germanium selenium nanomaterial was grown by the flux method,and two asymmetric structures were prepared from the perspective of device structure and energy band engineering.Combined with the excellent thermoelectric properties of the material itself,an asymmetric source-drain metal structure is designed to prepare a terahertz detector,which realizes the purpose of converting lowphoton energy terahertz waves into electrical signals.Experiments have tested the terahertz response speed,polarization dependence,and noise level,and analyzed the photo-thermoelectric response mechanism:the active region absorbs terahertz light and produces unbalanced hot carriers.Because different metals contact the electrodes,they are in the channel region.The temperature gradient difference distribution is formed,and the electric potential gradient is formed by the integration of the product of the Seebeck coefficient difference,and the electric signal extraction of the unbalanced carriers is realized.The experimental results show that the room temperature responsivity in the 0.26 THz band reaches 0.11 A W-1,the room temperature responsivity in the 0.10 THz band reaches 0.56A W-1,and the noise equivalent power(NEP)is lower than 150 pW Hz-1/2,which is more large linear dynamic range(linearity up to 36 dB).On the other hand,we fabricate zirconium germanium selenium-graphene heterojunction asymmetric structure devices by van der Waals stacking method,construct a built-in electric field to achieve efficient charge separation,compared to pure material devices,the detection sensitivity is significantly improved,with NEP reaching 14.6 pW Hz-1/2.3.As an allotrope of arsenic,black arsenic has a similar lattice structure and excellent electro-optical properties as black phosphorus:direct band gap,band gap tunability,broad-spectrum optical absorption capability,high mobility,and excellent stability,which provides the possibility of broadband visible-infrared-terahertz detection.We demonstrate photodetectors with pure black arsenic semiconductor,van der Waals stacked heterojunction structures of black arsenic semiconductor and graphene,achieving a broad spectral response.We analyze the photocurrent response mechanism with the aid of scanning photocurrent experiments(mapping)in the visible-NIR.The location of the photocurrent distribution of the pure black arsenic photodetector is mainly at the material-metal electrode contact interface,which is due to the photoelectric effect of laser radiation at the inhomogeneous channel location;while the photocurrent distribution of the black arsenic-graphene heterojunction device is mainly located in the heterojunction junction region,which is The built-in electric field in the heterojunction region effectively separates the electron-hole pairs due to the visible-near-infrared light excitation electron interband jumping.In addition,the room temperature stability of the black arsenic devices is experimentally found to be much higher than that of the currently popular black phosphorus crystal materials.