The Study Of Infrared And Terahertz Photoelectric Devices Based On Low-dimensional Quantum Structures

Low-dimensional nanomaterials is a material with the geometry size in the range from 0.1 nm to 100 nm,such as graphene,quantum dots,carbon nanotubes,nanowires and so on.Due to the effect of the size limited,when the geometry size is comparable with the quantum characteristic length,like electron mean free length.they exhibit some unique and excellent performances and become one of the important driven forces for the development in many fields.Metamaterials is an artificial materials composed of periodic subwavelength structure unit.Its electromagnetic characteristics not only depend on composition of the unit cell,but also relate to the shape and the size of the geometry.So its electromagnetic response can be modulated by artificial design and be fabricated by the micro-and nano-technology.In recent years,terahertz technology has become a new hot spot of the research frontiers due to its unique physical properties,and a plethora of terahertz sources,modulators and detectors have been designed and proposed.The low dimensional materials based terahertz devices can be studied as the unceasing advances of the microand nano-fabrication technology.In this paper,we mainly focus on the study of infrared and terahertz photoelectric devices based on the low-dimensional quantum structures,including the terahertz modulators based on the graphene metamaterials,the Bi2Se3 terahertz detectors,guided mode resonance based quantum well infrared detector and the Mo S2 nanosheet photodetectors with visible-infrared response.The main content is listed as follows:1.In order to achieve active modulation of the electromagnetic wave in the terahertz region,a compound structure composed of the graphene and split ring structure was fabricated.A series of modulation depth corresponding the frequency and amplitude are obtained by the bias voltage regulating the graphene Fermi level,which will be promote the development of the modulators in the field of wave shaping and the wave division multiplexer.The frequency and amplitude modulation depth can up to 60% and 98% with the two incident polarization,respectively.Moreover,by introducing the asymmetry of the metamaterial’s structure,an electromagnetically induced transparency(EIT)effect can be achieved and the group index are more than 1200 and 2000 with the two incident polarization,realizing a strong slow light effect and enhancing the interaction between the incident light and the graphene metamaterial.Besides,we interpret the electromagnetic induced transparency with the coupled Lorentz oscillator model.2.In order to achieve the terahertz detection with high responsivity,the subwavelength structure integrated topological insulators terahertz detectors have been fabricated.The Bi2Se3 flakes is transferred onto Si O2/Si substrate.Then,the Cr/Au subwavelength structure and the contact is formed by ultra-violet lithography and the electron beam evaporation.The photocurrents origin from the asymmetric scattering of the surface states electron when terahertz radiation illuminates the topological insulators at the self-powered mode.The subwavelength structure is used to couple the incident electromagnetic wave in the free space into the localized SPPs,enhancing the interaction between the incident terahertz radiation and the topological insulators.The responsivity and the response time of the MTM-based terahertz detector are 75 A/W and 60 ms with the self-powered mode,respectively.Moreover,the responsivity of the terahertz detectors can be further increased by imposing external voltage between the source and drain,which can improve the photoconductive gain in our structure.The terahertz response of this device origining from the surface states of the topological insulators can be further verified by the experiment of the infrared light(785 nm)pumping the terahertz detector,paving the way for the terahertz detection utilizing the surface states of the topological insulators.3.To achieve the infrared hyperspectral detection with high responsivity,fine spectral resolution and a wide spectral range,all-dielectric resonant waveguide based quantum well infrared photodetectors are proposed.Compared to the conventional metallic plasmonic enhanced structure,the coupling of the electron state in quantum well with the incident light can be greatly enhanced due to the absence of the Ohmic loss.The resonant absorption spectra are studied at the infrared region using the FDTD method.The dielectric grating in this structure is used to couple the incident electromagnetic wave in the free space,forming the guided mode resonance in the quantum well active region and enhancing the absorption of quantum well,improving the performance of the photodetector.Without Ohmic loss,the guided mode resonances lead to highly efficient absorption of the field power by the quantum wells and high Q factors for narrow spectral widths.Close to 100% resonant absorption with spectral resolution finer than 100 nm and a hundred channels could be achieved in the wavelength range from 6-10 mm.When the incident wavelengths deviate from the intrinsic absorption range of the quantum wells,a decrease in absorption coefficient causes an increase in Q factor and in mode intensity that would compensate the absorption power.As a result,a three-fold extension of the absorption range is demonstrated.4.To achieve the photodetector in the visible and infrared region with high responsivity and fast speed,in this work,Mo S2-based FETs are fabricated using mechanical cleavage and standard photolithographic and metal evaporation techniques,and the detector exhibits a good ohmic contact.We show that the multilayer molybdenum disulfide photodetector has a fast photoresponse as short as 42 ms.The large photocurrent with the responsivity of 59 A/W for the wavelength of 532 nm was also measured.Besides,we investigated relationship between the device’s response time and the Mo S2 flakes’ thickness.The response time decreases with the increasing Mo S2 thickness,which is due to increased screening of the interface trap states to capture or scatter off photocarriers.The devices showed a good response time up to 15 nm and remain almost unchanged when the thickness further increases,which indicates that the bulk carrier transport dominates over the interface carrier transport,providing an effective approach to achieve infrared detection with high responsivity and fast response.