太赫兹波具有穿透、安全、光谱分辨等独有的特性，使其在天文学、医学、生物学、安保、军事等多个学科和领域中有着广阔的应用前景。一直以来太赫兹探测器件的性能制约了太赫兹光谱的广泛应用。针对传统的太赫兹探测工作波长和响应性能存在的缺陷，本论文基于石墨烯等离激元对太赫兹波的响应，建立描述吸收的模型，提出计算结构电场分布的方法，探索如何将器件的光吸收和响应率最大化，以实现对太赫兹光的室温可调高效探测。本论文的主要研究成果如下： 1.利用描述等离激元光电导特性的Lorentz-Drude模型研究了石墨烯／金属衬底的复合结构。基于二维石墨烯的厚度，将其看作有损耗的界面，结合传输矩阵法和菲涅耳公式，获得了等离激元吸收的计算表达式，并给出了全吸收和无吸收的条件，解释了当入射光的波长发生变化时金属衬底的石墨烯结构对光的吸收会从100％降低到0％，并分析了只有某些模式增强的原因。为了使器件结构进一步具备可调的近完美吸收，构造基于石墨烯／介质的类似一维光子晶体的堆积结构，这种结构会在低频波段产生光子禁带。通过调控堆积结构中的石墨烯费米能级(化学势)，可以调控这一光子禁带的宽度以及反射光的相位，保证在吸收峰频率改变时，吸收始终>80％。因此，通过改变堆积结构中的石墨烯费米能级，控制反射光的相位，为人为有选择性地同时对几个模式进行增强，实现可调的多模式强吸收提供理论依据。 2.通常太赫兹的目标信号都比较弱，从太赫兹光电转换的机制来说，太赫兹探测器的探测率都与光敏元的光场强度相关。因此，要实现对弱信号光的探测，就需要极大地增强光敏元的局域场强度。通过构建金属结构，即使在不激发类等离激元(spoof surface plasmon，SSP)的频率下，也可以通过类等离激元产生局域场。在金属结构的一阶SSP以内，由于太赫兹局域场集中在金属结构端点，在端点下方放置石墨烯结构，石墨烯的等离激元将与金属表面的局域场相互作用，在相同有效面积下，吸收将被增强。 3.通过金属条人工周期结构调控石墨烯上等离激元的激发，这样周期性排布的有金属／无金属部分的石墨烯沟道可以看成横向一维等离激元晶体结构，则可以计算激发的等离激元电场分布。由载流子输运的欧拉方程和连续性方程可以得到载流子浓度、速度和电场分布的关系，于是可以对等离激元牵引(Drag)效应和棘轮(Ratchet)效应的光电流和响应率进行计算。计算结果表明驻波导致的等离激元牵引效应产生的响应率比单向等离激元牵引效应的响应率弱了一个数量级以上，而等离激元棘轮效应的响应率则可以达到理论最大值。另外，假如考虑超高迁移率的石墨烯，等离激元棘轮效应的响应率相比热电效应的响应率有着数量级的提升。对于目前用CVD可以制备的石墨烯，由于石墨烯的迁移率比较低，热电效应的响应率比等离激元棘轮效应的响应率要大。 关键词：石墨烯，等离激元，太赫兹，探测器

 Terahertz (THz) waves have unique properties such as penetration, safety and spectral resolution which make them valuable and promising in the aspects of astronomy, medicine, biology, communication, security and military, etc. The extensive application of THz waves has long been limited by the performances of THz detectors. In order to overcome the disadvantages of the operating wavelength and the responsivities of traditional THz detectors, this thesis proposes to detect the THz waves based on graphene plasmons. A model which describs the absorption of graphene plasmons and an approach to calculating the distribution of the electric field in certain structures are proposed. Our works aim at maximizing the absorption and the responsivity of graphene plasmonic terahertz detectors, so that efficient room-temperature tunable detection of THz waves can be realized. The main researching results of this thesis are listed as follows: 1.Graphene is considered as a dissipative interface with no thickness and then its conductivity is described by the Lorentz-Drude model. Combining the conductivity model with the transfer matrix method and Fresnel equations, the absorption of the structures with metal reflectors is well described. The conditions for complete absorption and zero absorption are given by this method, which explains the reason for the decrease of the absorption from 100% to 0% when the frequencies of the peaks change. The phenomenon that not all of the modes are enhanced can also be explained. In order that the detector has tunable near-complete absorption, we propose to use graphene/dielectric stacking structure, which produces a photonic bandgap within the low frequency region. The width and the phase of the reflection in the photonic bandgap can be tuned by tuning the graphene Fermi energy in the stacking structure, and then the absorption of the 1〓 order mode can always be larger than 80% in the tuning range. Therefore, the active tuning of the phase of the reflectied light can be realized by the active tuning of the graphene Fermi level in the stacking structure, offering active enhancement of several modes and theoretical support of realizing tunable multimode enhancement. 2.Generally speaking, the signals of THz waves are weak. As far as the mechanisms of the THz photo-electric conversions are concerned, the detectivity of THz detectors is related with the strength of the localized electric field of the photosensitive elements. Therefore, the localized electric field of the photosensitive elements should be greatly enhanced in order to realize detection of weak incident light. Localized electric field can be generated by the spoof surface plasmon (SSP) of metals in the absence of a stabilized SSP mode by constructing metal structures. The localized THz electric field will be concentrated at the tips of the metal structures when the frequency of incident radiation is close to or lower than that of the 1〓 order SSP mode. Inserting structured graphene below the tips of the metal structures, the graphene plasmon modes within the 1〓 order SSP mode will be greatly enhanced because of the interaction between graphene plasmons and the localized electric field. Therefore, for devices with and without such metal structures, the device with such metal structures will show enhanced absorption if the effective areas are the same. 3.Plasmons can be excited by depositing metal gratings over graphene with finite seperation. The electric field distribution in the graphene channel can be calculated by considering the grating gated graphene as lateral one-dimensional plasmonic structure. The relations between the carrier density, the carrier velocity and the electric field can be calculated by the Euler, continuity and Poisson equations, so that the photocurrent and responsivity of the plasmon drag effect and the plasmon ratchet effect can be calculated. The results show that the responsivity of the plasmon drag effect of biased standing wave can be one order of magnitude weaker than that of unidirectional plasmons, while the responsivity of the plasmon ratchet effect can reach the maximum value predicted in references. Besides, for graphene with ultrahigh mobility, the responsivity of the plasmon ratchet effect can be 5 orders of magnitude larger than that of the PTE effect, while for currently available graphene fabricated by chemical vapor deposition, the responsivity of the PTE effect can be larger than that of the plasmon ratchet effect because the mobility of graphene is comparatively lower. Key Words: Graphene, plasmon, Terahertz wave, detector