SST: Mid Infrared Avalanche Photodiodes Based on Nanoscale Quantum Dots

这项工作的目的是开发一种高灵敏度的中红外传感器，称为QDAP（量子点雪崩光电二极管），基于纳米级量子点的子带间跃迁与雪崩倍增。子带间量子点传感器被认为是中红外领域的一项有前途的技术，因为它们基于成熟的GaAs技术，对正常入射辐射敏感，表现出可用于高光谱成像的大量子受限stark效应，并且具有比量子阱对应物更低的暗电流。然而，量子点探测器的低量子效率限制了它们的工作温度在70-80K。最先进的光子探测器基于窄带隙碲化汞镉（MCT）材料，在相同的工作温度下提供更高的单像素性能。然而，与固有缺陷相关的非均匀性问题限制了基于mct的焦平面阵列的发展。目前，所有中红外光子探测器都在低温（4-100K）下工作，并且具有复杂的冷却要求，包括多级sterling冷却器。高灵敏度中红外传感器可以在相对便宜的Peltier冷却器（150-250K）达到的温度下工作，这将是一个重大的技术飞跃，并将显著降低红外传感器和成像系统的成本和复杂性。根据我们的初步计算，我们估计QDAPs的工作温度将比传统的QD探测器高约100K。智力优势：在本提案中，提出了一种称为QDAP的新型器件，预计它比传统的QD探测器具有更高的灵敏度和更好的性能。在QDAP中，子带间量子点探测器通过隧道势垒与雪崩光电二极管（APD）耦合。虽然隧道势垒比器件QD部分的光电流更有效地降低了暗电流，但APD提供了提高信噪比（SNR）所需的光电流增益。特别是，APD提供了克服读出噪声所需的大增益，并实现了显着增强的射击噪声限制信噪比，这是以雪崩过量噪声为代价的。通过这种新颖的组合，我们可以在相同的温度下获得更高的灵敏度（D*响应度），或者在更高的工作温度下具有相当的性能。此外，APD可以在线性模式或盖革模式（单光子计数模式）下工作。从灵敏度的角度来看，光子计数系统被认为是光子传感技术的终极。这种传感器对于传感从显微镜和医学成像到光子通量非常有限的天文学和天体物理学等许多科学和工程领域的超低能级图像和信号非常有用。目前还没有用于中红外波段的单光子探测器。PI的小组最近报道了三种彩色量子点探测器，工作在中波红外（MWIR, p ~ 4m），长波红外和甚长波红外。这些设计将被整合到本项目提出的传感器中，以实现高灵敏度的多色探测器。对所提出结构的理论建模表明，量子点探测器与同质结构和异质结构APD的耦合是可能的，从而为通过APD倍增区的带隙工程优化APD提供了线性或盖格模式工作的机会。该项目借鉴了具有积极合作记录的pi的互补专业知识。自组装InAs/(In,Ga)As量子点apd将由新墨西哥大学（UNM）的pi进行设计、优化、生长、制造和表征。设备的盖格模式操作测试将与谢菲尔德大学的研究人员合作进行（附支持信）。更广泛的影响：pi对课堂教育和让本科生参与理论和实验室研究都有承诺。去年，有四名本科生（包括两名少数民族学生和两名由NSF REU项目资助的学生）参与了他们的研究活动。这一传统将在这个项目中继续下去，并有当地高中生的额外参与。此外，该项目的结果将影响pi在光电器件和光通信方面已经开发的两门课程。这些课程的目的是在Web-CT平台上发布，并在多个机构同时提供。此外，通过我们与智利康塞普西翁大学的国际合作伙伴的互动，我们的学生将有机会在智利的TIGO天文台设施接受额外的实践培训，该设施使用近红外盖格模式apd进行卫星跟踪。该项目将在新墨西哥纳米科学联盟和美国国家科学基金会的国家纳米技术基础设施网络（NNIN）计划等论坛上导致更广泛的知识传播，新墨西哥大学是其中的一个团队成员。

0428756KrishnaThe aim of the proposed effort is to develop a high sensitivity, mid-infrared sensor called QDAP (Quantum Dot Avalanche Photodiode), based on intersubband transitions in nanoscale QDs in conjunction with avalanche multiplication. Intersubband QD sensors are perceived as a promising technology for mid infrared regime since they are based on a mature GaAs technology, are sensitive to normal incidence radiation, exhibit large quantum confined stark effect that can be exploited for hyperspectral imaging, and have lower dark currents than their quantum well counterparts. However, the low quantum efficiency of QD detectors has limited their operating temperature to 70-80K. State of the art photonic detectors are based on the narrow bandgap mercury cadmium telluride (MCT) material, which offer higher single pixel performance at the same operating temperature. However, non-uniformity issues associated with native defects have limited the progress of MCT-based focal plane arrays. Presently all mid infrared photonic detectors operate at cryogenic temperatures (4-100K) and have complicated cooling requirements that include multi-stage sterling coolers. A high-sensitivity mid infrared sensor operating at temperatures achievable by the relatively inexpensive Peltier coolers (150-250K) would represent a major technological leap and lead to a significant reduction in the cost and complexity of infrared sensors and imaging systems. Based on our preliminary calculations, we estimate that the operating temperature of QDAPs would be about 100K higher than that of conventional QD detectors.Intellectual Merit: In this proposal, a novel device called QDAP is proposed which is expected to have a higher sensitivity and improved performance over conventional QD detectors. In the QDAP, an intersubband quantum dot detector is coupled with an avalanche photodiode (APD) through a tunnel barrier. While the tunnel barrier reduces the dark current more effectively than the photocurrent in the QD section of the device, the APD provides the necessary photocurrent gain required to increase in the signal-to-noise ratio (SNR). In particular, the APD provides the large gain necessary to overcome the readout noise and achieve a significantly enhanced shot-noise-limited SNR, which comes at the slight expense of the avalanche excess noise. With this novel combination, we can achieve a higher sensitivity at the same temperature (D* responsivity) or have a comparable performance at higher operational temperatures. Moreover, the APD could be operated in the linear mode or in the Geiger mode (single photon counting mode). Photon-counting systems are regarded as the ultimate in photon-sensing techniques from a sensitivity perspective. Such sensors would be extremely useful for sensing ultralow-level images and signals in many scientific and engineering fields stretching from microscopy and medical imaging to astronomy and astrophysics, where the photon flux is very limited. Presently there are no single photon detectors available for the mid infrared regime. The PI`s group has recently reported three color QD detectors operating in the mid wave infrared (MWIR, p ~ 4m), long wave infrared and very long wave infrared. These designs would be incorporated into the sensor proposed in this project to realize multi-color detectors with high sensitivity. Theoretical modeling of the proposed structures has revealed that the coupling of the QD detectors with both homostructure and heterostructure APDs is possible, thereby providing the opportunity for optimizing the APD for either linear- or Geiger-mode operation through bandgap engineering of the APDs multiplication region. This project draws from the complementary expertise of the PIs who have an established record of active collaboration. The self- assembled InAs/(In,Ga)As quantum-dot APDs will be designed, optimized, grown, fabricated, and characterized by the PIs at the University of New Mexico (UNM). Testing of the Geiger-mode operation of the devices will be undertaken in collaboration with researchers at the University of Sheffield (support letter attached).Broader Impacts: The PIs have a commitment both to classroom education and to involving undergraduates in theoretical and laboratory research. Last year, the PIs involved four undergraduates (including two minority students and two students sponsored by the NSF REU program) in their research activities. This tradition will continue in this project with the additional participation of local high school students. Additionally, results from this project will impact two courses that have already been developed by the PIs in optoelectronic devices and optical communication. These courses are intended for launch on Web-CT platforms and be offered at multiple institutions simultaneously. In addition, through our interaction with our international collaborators at the Univesidad de Concepcion, Chile, our students will have an opportunity to receive additional practical training at the TIGO observatory facility in Chile, in which near infrared Geiger-mode APDs are used for satellite tracking. The project would lead to a broader dissemination of knowledge in forums such as the New Mexico Nano-Science Alliance and NSF's National Nanotechnology Infrastructure Network (NNIN) program, of which UNM is a team member.