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Defect Reduction Techniques for Large Format Infrared Detector Materials


OBJECTIVE: The overall objective of this effort is to develop innovative solutions to significantly decrease the defect and dislocation sizes and densities in large format (>25 cm^2) II-VI compound semiconductor infrared detector materials. Emphasis shall be given to detectors operating in the short through mid-long wavelength regime (~10 micron cut-off). DESCRIPTION: The Missile Defense Agency (MDA) is interested in technology developments in support of advanced space sensor systems. Space-based sensors operate in low background environments where the minimization of noise is paramount to mission operation. Sensor bands from the short through mid-long wavelength infrared (IR) wavelengths are of interest. Large format infrared focal plane arrays based on mercury cadmium telluride (MCT) have been demonstrated at>25 cm^2 with acceptably low levels of defects and dislocations when grown on lattice-matched cadmium zinc telluride (CZT). However, MCT grown on less costly, alternative substrates such as Si exhibit significantly higher numbers of dislocations and defects, despite the use of multiple buffer layers. Dislocations and defects in infrared detector materials are manifested as noise, defective pixels, and current leakage, limiting the FPA operability characteristics. They also propagate with thermal cycling, limiting the service lifetimes of infrared focal plane arrays. These defects and dislocations are highly influenced by non-optimal surface interfaces, with contributing factors such as lattice mismatch, surface roughness, coefficient of thermal expansion mismatch, and the presence of an oxide layer. The Ballistic Missile Defense System (BMDS) requires reliable, high performance, high sensitivity and low noise space-based sensors which are affordable and producible. Atomic hydrogen passivation of substrates prior to epitaxial growth, and/or detector and cap layers prior to passivation may be a viable solution for reducing defects. Innovative methods such as, but not limited to atomic hydrogen etching, are being sought to affordably reduce dislocations and defects in IR detector materials. An offeror may submit multiple proposals with unique approaches. PHASE I: Identify and investigate unique process designs and/or production process changes or additions suitable for IR detector fabrication that will result in a significant reduction in defect and dislocation size and densities, while retaining or enhancing performance and operational lifetimes. Hydrogenation of interfaces has been proposed as a potential concept; other approaches are encouraged. Theoretical and experimental proof-of-concept, including stability of the process during processing and thermal cycling shall be demonstrated and documented. A deliverable detector (discrete or array) or design available to the government for additional characterization is highly desirable. Offerors are strongly encouraged to work with infrared component contractors to help ensure applicability of their efforts and begin work towards technology transition, either by license or service. PHASE II: Using the resulting process, techniques, and/or process changes or additions developed in Phase I, verify and optimize these changes in a prototype fashion, on or off a product line to demonstrate the feasibility and efficacy of the technique. The contractor should keep in mind the goal of commercialization of this innovation for the Phase III effort, to which end they should have working relationships with, and support from, infrared component contractors. PHASE III: Either solely, or in partnership with a suitable production foundry, implement, test and verify in full scale the Phase II demonstration item as an economically viable production technique. Demonstration would include, but not be limited to, demonstration in a real product line with the resulting IR detector / focal plane array testable in a system level test-bed against system performance criteria. This demonstration should show near-term application to BMDS systems, subsystems, or components. DUAL USE/COMMERCIALIZATION POTENTIAL: Innovations developed under this topic will benefit both DoD and commercial space, airborne, and terrestrial programs. Possible uses for these products and techniques include surveillance, astronomy, mapping, weather monitoring, and earth resource monitoring. Enhancements to imaging quality and higher product yields show significant potential for increased applications. REFERENCES: 1. K.S. Ziemer, C.D. Stinespring, L.S. Hirsch, and T.H. Myers,"Characterization of Atomic Hydrogen-Etched HgCdTe Surfaces", Journal of Crystal Growth, Vol. 191, pp. 594-598, 1998. 2. L.S.Hirsch, K.S. Ziemer, M.R. Richards-Babb, C.D. Stinespring, T.H. Myers, and T. Colin,"The Use of Atomic Hydrogen for Low Temperature Oxide Removal from HgCdTe", Journal of Electronic Materials, Vol. 27, No. 6, pp. 651-656, 1998. 3. L.S.Hirsch, Zhonghai Yu, S.L. Buczkowski, and T.H. Myers,"The Use of Atomic Hydrogen for Substrate Cleaning for Subsequent Growth of II-VI Semiconductors", Journal of Electronic Materials, Vol. 26, No. 6, pp. 534-541, 1997.
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