Collaborative Research: Silver-Based Colloidal Quantum Dot Devices for Ubiquitous Mid-Wavelength Infrared Sensing

第一部分：与可见光或近红外夜视摄像机不同，在中波长红外（MWIR）下工作的光电探测器可以通过雾、薄雾和其他遮挡物成像，并且不需要外部照明源，因为它们可以仅通过感知物体发射的辐射来捕获图像。这些传统上用于军事监视的MWIR光电探测器正在发现越来越多的应用，从夜间驾驶辅助，搜索和救援，生物医学成像到危险化学品的环境监测。然而，现有的MWIR技术非常昂贵，不适合这些应用，因为它们需要低温冷却才能达到高灵敏度，使得探测器体积大，重量重，功耗大。提出的研究旨在实现基于新发现的红外胶体量子点（CQDs）的颠覆性光电探测器技术，该技术将允许高温操作，从而消除尺寸，重量和功耗障碍，以大规模采用。此外，CQD器件的加工与成熟的硅技术高度兼容，这将允许在晶圆规模上单片制造光电探测器，从而大幅降低成本。该项目高度跨学科的性质也将为不同层次的学生创造独特的教育机会，这将有助于增加未被充分代表的少数民族进入大学的科学和工程项目，并加强我们在美国的STEM劳动力。第二部分：本研究的总体目标是全面了解基于硫系银CQDs的光电二极管的器件物理，以演示高温，高灵敏度的MWIR光电二极管。由紧密排列、强耦合的硫系银CQDs组成的薄膜具有通过俄歇抑制实现光电探测器高温工作的良好潜力。然而，实现高性能基于cqd的光电二极管的主要挑战在于无法获得具有合适波段对准的材料组合以及缺乏对光电二极管结构中器件操作的理解。这项研究虽然是一个渐进的器件研究，但将研究一种基于两种类型的cqd形成异质结的新方法，这将使实现高器件性能所需的能级微调成为可能。基于这种方法，本项目将对俄歇抑制和热生成载流子产生的暗电流以及载流子输运、重组和光电二极管中光学生成载流子的捕获产生基本的理解。该项目的成果有可能实现低成本、高性能的MWIR传感技术，该技术将在广泛的应用中得到普遍应用。此外，该MWIR CQD研究与现有的可见光、近波长和短波长的红外CQD相结合，将直接促进多光谱成像焦平面阵列的发展。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。

Part 1:Unlike visible or near-infrared night vision cameras, photodetectors operating in the mid-wavelength infrared (MWIR) can image through fog, mist, and other obscurants and do not require an external source of illumination as they can capture images solely by sensing the radiation that objects emit. These MWIR photodetectors that have been traditionally used for military surveillance are finding growing number of applications ranging from night driving assist, search-and-rescue, biomedical imaging, to environmental monitoring of hazardous chemicals. However, existing MWIR technologies are prohibitively expensive and ill-suited for these applications as they require cryogenic cooling to achieve high sensitivity, making the detector bulky, heavy, and consume large power. The proposed research aims to enable a disruptive photodetector technology based on newly discovered infrared colloidal quantum dots (CQDs) that will allow high temperature operation thereby removing the size, weight, and power consumption barriers to wide-scale adoption. Furthermore, the processing of CQD devices is highly compatible with mature silicon technology that will allow monolithic fabrication of photodetectors at the wafer scale leading to dramatic reduction in cost. The highly interdisciplinary nature of this project will also create unique educational opportunities for various levels of students that will help increase the pool of underrepresented minorities entering science and engineering programs at colleges and strengthen our STEM work force in the US.Part 2:The overall goal of this research is to gain a comprehensive understanding of device physics of photodiodes based on silver chalcogenide CQDs to demonstrate high temperature, high sensitivity MWIR photodiodes. Films composed of close-packed, strongly-coupled silver chalcogenide CQDs have the promising potential to enable high temperature operation of photodetectors through Auger suppression. However, the major challenges in realizing high performance CQD-based photodiodes lies in the unavailability of material combinations with suitable band alignment and the lack of understanding of device operation in photodiode structures. This research, though a progressive device study, will investigate a new method of forming heterojunctions based on two types of CQDs which will enable fine tuning of energy levels needed for achieving high device performance. Based on this approach, this project will generate fundamental understanding of Auger suppression and dark current arising from thermally generated carriers as well as carrier transport, recombination, and trapping of optically generated carriers in photodiodes. The outcomes of this project could potentially enable a low-cost, high performance MWIR sensing technology that will be ubiquitously utilized in a broad range of applications. Moreover, this MWIR CQD research, combined with existing visible, near-, and short-wavelength infrared CQDs, will directly contribute to the development of multispectral imaging focal plane arrays.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.