二维电子气等离激元太赫兹波器件

固态等离激元太赫兹波器件正成为微波毫米波电子器件技术和半导体激光器技术向太赫兹波段发展和融合的重要方向之一。本综述介绍AlGaN/GaN异质结高浓度和高迁移率二维电子气中的等离激元调控、激发及其在太赫兹波探测器、调制器和光源中应用的近期研究进展。通过光栅和太赫兹天线实现自由空间太赫兹波与二维电子气等离激元的耦合,通过太赫兹法布里-珀罗谐振腔进一步调制太赫兹波模式,增强太赫兹波与等离激元的耦合强度。在光栅-谐振腔耦合的二维电子气中验证了场效应栅控的等离激元色散关系,实现了等离激元模式与太赫兹波腔模强耦合产生的等离极化激元模式,演示了太赫兹波的调制和发射。在太赫兹天线耦合二维电子气中实现了等离激元共振与非共振的太赫兹波探测,建立了太赫兹场效应混频探测的物理模型,指导了室温高灵敏度自混频探测器的设计与优化。研究表明,基于非共振等离激元激发可发展形成室温高速高灵敏度的太赫兹探测器及其焦平面阵列技术。然而,固态等离激元的高损耗特性仍是制约基于等离激元共振的高效太赫兹光源和调制器的主要瓶颈。未来的研究重点将围绕高品质因子等离激元谐振腔的构筑,包括固态等离激元物理、等离激元谐振腔边界的调控、新型室温高迁移率二维电子材料的运用和高品质太赫兹谐振腔与等离激元器件的集成等。

Terahertz-wave devices based on plasmons in two-dimensional electron gas

Solid-state terahertz plasma devices are becoming one of the important research areas in which both solid-state microwave/millimeter-wave electronics and semiconductor laser technologies are being developed and merged towards the terahertz frequency regime. In this review, we introduce the manipulation, excitation and probing of two-dimensional-electron-gas(2DEG) plasmons in AlGaN/GaN heterostructure, and report the recent progresses in the implementation of plasmon physics in terahertz detectors, modulators and emitters. The coupling between the plasmon modes and the terahertz electromagnetic waves in free space are realized by using grating coupler, antenna and terahertz Fabry-Pérot cavity which further modulates the terahertz electromagnetic modes and enhances the coupling. The dispersion relationship of gate-controlled plasmon modes are verified in grating-coupled 2DEG. Strong coupling between the plasmon modes and the terahertz cavity modes and hence the formation of plasmon-polariton modes are realized in a grouping-coupled 2DEG embedded in a Fabry-Pérot cavity. Based on the same grating-coupled 2DEG, terahertz modulation with high modulation depth and terahertz plasmon emission are observed. In antenna-coupled 2DEG field-effect channel, both resonant and non-resonant excitation of localized plasmon modes are observed by probing the terahertz photocurrent/voltage. A terahertz self-mixing model is developed for antenna-coupled field-effect terahertz detector and provides a guideline for the design and optimization of high-sensitivity terahertz detectors. Our studies indicate that room-temperature, high-speed and high-sensitivity terahertz detectors and the focal-plane arrays can be developed by using the non-resonant plasmon excitation in antenna-coupled field-effect channel. However, the high damping rate of solid-state plasma wave is yet the main hurdle to overcome for plasmon terahertz emitters and modulators both of which rely on the resonant plasmon excitation. The formation of high-quality-factor plasmon cavity including the solid-state plasma physics, manipulation of the boundary conditions of plasmon cavity, utilization of new high-electron-mobility two-dimensional electronic materials and high-quality, small-mode-volume terahertz resonant cavity, etc. would be the focus of future research.