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

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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.