Detection of the terahertz (THz) electromagnetic spectrum(wavelengths range 0.03–3 mm) is a promising technique for a large variety of strategic applications, such as biomedical diagnostics and process, quality control, homeland security, and environmental monitoring, etc. Graphene has been recognized internationally to have dominant advantages in photodetectors operating due to its high carrier mobility, gapless spectrum, and frequency-independent absorption coefficient. Graphene photodetector operating in the THz region has been extensively studied with great interests. A graphene microcavity photodetector with THz electromagnetic spectrum is demonstrated in this paper, and its responsivity and detectivity under THz electromagnetic spectrum are evaluated. In the designed device, we adopt a distributed bragger reflection (DBR) consisting of two semiconductor materials SiO2 and TiO2 to form an alternating cavity with high-finesse planar, sandwich the absorbing graphene layer between the cavity’s top and bottom layers, and design the DBR’s reflectivity by the optical transmission matrix method. The monolayer graphene’s optical absorption mechanism of the THz radiation spectrum is studied by the conductivity matrix and Maxwell’s equations with the electromagnetic boundary conditions. Graphene’s transfer matrix and absorption coefficient equation are further derived. It is found that at THz region, graphene’s conductivity plays an important role in its absorptionand its absorption is 9–22 times enhanced compared with that at the visible region. An optical absorption model of microcavity-enhanced graphene photodetector at THz region is established. The photodetector’s absorption rate and responsitivity are analyzed specifically. Theoretical analysis shows that absorption rate is symmetrical to the microcavity’s center position and changes periodically, and the shift of the microcavity length influences the period numbers. The maximum rate of the photodetector’s absorption reaches 0.965 at 0.12 THz, which increases 93%compared with its maximum absorption rate 0.5 with no cavity. The optimal structure parameters for the designed photodetector are as follows, the top and bottom mirror’s reflectivity are 0.928 and 0.998 respectively, the microcavity length is 2.5 mm, the graphene is 0.035 mm away from the top mirror. Under the optimal structure, the photodetector’s responsivity reaches 236.7 A/W, and its full width at half maximum reaches 0.035 THz. The designed graphene microcavity photodetector can exhibit high responsivity and detectivity in THz radiation spectrum.%由于石墨烯在太赫兹波范围内只发生带内跃迁,相比在可见光范围内,其光学吸收特性有显著优势,通过集成石墨烯与谐振腔,将太赫兹波限制在腔内,可进一步增强石墨烯对太赫兹波的吸收.采用麦克斯韦方程组并结合电磁场边界条件,研究了单层石墨烯在太赫兹波段范围内的光吸收机理；推导出石墨烯的传输矩阵和吸收系数方程,发现在太赫兹波段石墨烯的吸收是在可见光波段吸收的9—22倍；通过建立谐振腔型石墨烯光电探测器在太赫兹波段的光吸收模型及求解探测器吸收率方程,发现在0.12 THz处,吸收率可达0.965,相比无腔状态下石墨烯在太赫兹波段的最大吸收率0.5,提高了93%；优化设计器件结构参数并表征,最终器件响应度最高达到236.7 A/W,半高全宽为0.035 THz.理论分析表明,采用谐振腔型石墨烯光电探测器对太赫兹波进行探测,具有高吸收率、高响应度.研究结果对于太赫兹谐振腔型石墨烯光电探测器的设计和应用提供了理论参考.
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