CAREER: Unconventional Mid-infrared and Terahertz Sources Employing Graphene Plasmonics and Intersubband Transitions in Quantum Wells

非技术描述：中红外（MIR）到太赫兹（THz）光谱范围具有其独特而关键的科学和技术重要性。在MIR - THz光谱范围内，无数的分子物种都具有像“指纹”一样的强吸收谱线，因此在这一光谱范围内可以开发出灵敏度和选择性优越的基于吸收光谱的分子传感技术。此外，随着通信带宽需求的快速增长，无线通信技术正从GHz频率范围向太赫兹频率范围发展。因此，MIR到THz范围的研究进展将继续推动医疗保健、国土安全、环境保护、能源生产、通信和物联网等重要领域的技术和应用发展。然而，目前用于该光谱范围的器件技术并不像用于其他光谱范围的器件技术那样多样化和成熟。与主要研究者的长期职业目标一致，该career提案旨在基于非常规器件架构和工作原理开发新型MIR和太赫兹光源。具体来说，所提出的光源将协同结合石墨烯等离子体和量子阱中子带间跃迁的优势，这是MIR到太赫兹光谱范围内两种强大的器件技术。利用量子阱中子带间跃迁和石墨烯表面等离子体（GSPs）之间的强相互作用，有望开发出性能更高、成本更低、功能更广的器件。该计划将提供宝贵的机会和资源，帮助参与的学生成为下一代科学家和工程师，在竞争激烈的全球舞台上发挥领导作用。首席研究员还将积极组织和参与推广活动，以传播研究成果和/或激发K-12学生对STEM学科的兴趣。这些活动的目的是吸引不同背景的学生参与，包括来自代表性不足群体的学生。技术描述：这个拟议的CAREER项目旨在首先深入研究量子阱中GSP和子带间跃迁之间强相互作用的基本特性，随后利用所获得的知识开发两种非常规MIR和太赫兹源，即(1)石墨烯等离子体天线增强光源和(2)电泵浦GSP源。MIR或太赫兹GSPs与量子阱中谐振子带间跃迁之间的耦合建立了一个有趣的物理系统和一个新的设备应用平台。该项目将重点研究这些相互作用的几个基本方面，包括对跃迁选择规则的潜在修改、珀塞尔效应、相互作用强度对石墨烯载流子密度和结构几何形状的依赖，以及与非垂直跃迁相关的跃迁能量转移。全面了解这些方面对于后续的器件开发至关重要。传统的MIR和太赫兹光发射器存在辐射转换效率低的问题，其寿命比非辐射寿命长几个数量级。提出的石墨烯等离子体天线增强MIR和太赫兹光发射器旨在利用gsp和子带间跃迁之间的强相互作用，这有望导致辐射寿命的急剧减少，从而显着提高输出功率和功率效率。与通过光激发产生GSPs的传统方法相比，采用石墨烯等离子波导耦合子带间跃迁的装置是电泵表面等离子体源，它更紧凑，更便于在片上传感和通信等应用中使用。这两种类型的MIR和THz源都具有较大的频率可调性，这是石墨烯基器件的另一个关键优势。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Nontechnical description: The mid-infrared (MIR) to terahertz (THz) spectral range has its unique and crucial scientific and technological importance. Countless molecular species have strong and "fingerprint" like absorption lines in the MIR to THz spectral range, and consequently absorption spectroscopy based molecular sensing technologies with superior sensitivity and selectivity can be developed in this spectral range. Furthermore, as the demand for communication bandwidth keeps growing rapidly, wireless communication technologies are moving from the GHz frequency range towards the THz frequency range. Therefore, research advances in the MIR to THz range will continue to drive development of technologies and applications in important areas such as health care, homeland security, environmental protection, energy production, communications and internet of things. However, current device technologies for this spectral range are not as diverse and mature as those for the other spectral ranges. Aligned with the long-term career goals of the principle investigator, this CAREER proposal aims at developing new types of MIR and THz light sources based on unconventional device architectures and operating principles. Specifically, the proposed light sources will synergistically combine the advantages of graphene plasmonics and intersubband transitions in quantum wells, which are two powerful device technologies for the MIR to THz spectral range. Exploiting strong interactions between intersubband transitions in quantum wells and graphene surface plasmons (GSPs) is expected to lead to devices with improved performances, lower cost and extended functionalities. The proposed CAREER project will provide valuable opportunities and resources to help the participating students becoming the next-generation scientists and engineers who can play leading roles on the competitive global stage. The principle investigator will also actively organize and participate outreach activities which will disseminate the research outcomes and/or stimulate K-12 students' interests in the STEM disciplines. These activities will be designed to attract participation of students of diverse backgrounds, including those from the under-represented groups. Technical description: This proposed CAREER project aims at first thoroughly studying the fundamental properties of strong interactions between GSPs and intersubband transitions in quantum wells, and subsequently utilizing the obtained knowledge to develop two types of unconventional MIR and THz sources, which are (1) graphene plasmonic antenna-enhanced light emitters and (2) electrically-pumped GSP sources. Coupling between MIR or THz GSPs and resonant intersubband transitions in quantum wells establishes an intriguing physical system and a new platform for device applications. This project will focus on investigating several fundamental aspects of these interactions, including the potential modification of transition selection rules, the Purcell effect, the dependence of interaction strength on graphene carrier density and structure geometries, and the transition energy shift associated with non-vertical transitions. A comprehensive understanding of these aspects is crucial for the subsequent device development. Conventional MIR and THz light emitters suffer from the low efficiency of radiative transition process which has a lifetime by orders of magnitude longer than the non-radiative lifetime. The proposed graphene plasmonic antenna-enhanced MIR and THz light emitters aim at exploiting the strong interactions between GSPs and intersubband transitions, which are expected to lead to a drastic reduction of the radiative lifetime and hence a significant improvement of output power and power efficiency. In contrast to the conventional methods of generating GSPs via optical excitation, the proposed devices employing graphene plasmonic waveguides coupling to intersubband transitions are electrically pumped surface plasmon sources, which are much more compact and convenient to use in applications such as on-chip sensing and communications. Both types of proposed MIR and THz sources have large frequency tunability, which is another key advantage of graphene based devices.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.