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High Aspect Ratio Mesa Delineation of Antimonide Based Infrared Focal Plane Arrays for Improved Quantum Efficiency and Modulation Transfer Function (MTF)

Description:

TECHNOLOGY AREA(S): Electronics 

OBJECTIVE: Improve the performance of and yield of III-V antimonide-based dual band infrared detector focal plane arrays through the development of a high aspect ratio mesa delineation enabling improved optical fill factor, modulation transfer function (MTF), and uniformity. 

DESCRIPTION: III-V antimonide (Sb) - based compound semiconductors and superlattices are of great interest for high performance detectors in the entire infrared spectrum. They have tunable bandgaps, offer significant cost benefits, and can be made into very large formats. Additionally, they have flexible band structures. Using bandgap engineering, the potential for a wide range of applications exists including decreased Auger and tunneling rates, as well as suppressed generation-recombination and surface currents. However technical challenges still need to be addressed in order to fully realize the potential benefits of III-V antimonide based infrared detector materials. Dual-band focal plane arrays (FPAs) built with antimonide based Strained Layer Superlattice (SLS) materials are typically produced using partial delineation of the detector elements. Partial delineation has advantages in that the material is exposed to the high energy plasma for a shorter period of time affording a lower risk of plasma induced damage, and less material is removed leading to a higher overall optical fill factor. However, testing has shown that partial reticulation of SLS material has a negative impact on the MTF (a metric of detector performance) because of lateral diffusion of charge carriers. Full delineation of the detector mesas will prevent lateral diffusion improving the detector MTF, but is likely to reduce the optical fill factor and lower the quantum efficiency. A low temperature high aspect ratio delineation process compatible with standard photoresist mask formulation will be required to keep a high optical fill factor, prevent damage during delineation, and maintain high process yield. Achieving full delineation while maintaining high optical fill factor will likely require the investigation of high density plasma techniques such as inductively coupled plasma (ICP) for mesa delineation.1 Consideration of the impact of trench shape/profile on the optical fill factor will be a critical aspect in the development of a delineation process. A trench with a “v” shaped groove is desirable to incorporate total internal reflection and further increase the optical fill factor. The surface composition and morphology following the mesa delineation is another critical aspect. The etched surfaces must be smooth to avoid light scattering and loss of quantum efficiency. Many plasma based delineation techniques require a wet chemical clean up following the plasma etch due to deleterious deposits formed by the plasma. The ideal plasma delineation process would leave a clean smooth surface and not require a wet chemical clean.2,3 

PHASE I: Identify low temperature mesa delineation processes with high etch selectivity between the lithography mask and III-V semiconductor material capable of producing narrow high aspect ratio trenches between detector mesas. Demonstrate deep, > 10 m, delineation process on bulk semiconductor materials such as GaSb, InAs, and InSb or on dual band superlattice detector structures with top trench widths no greater than 4 m across. Partnering with a commercial FPA manufacturer is strongly encouraged to support the potential commercialization of the developed process. 

PHASE II: A detailed experimental study of delineation process parameters including surface morphology, composition, and profile. Apply the developed delineation process and demonstrate the performance on a dualband superlattice FPA with a U.S. Army relevant format of 512 x 512 or greater and pixel pitch between 8 and 15 m. 

PHASE III: The contractor shall pursue commercialization of the various technologies and EO/IR components developed in Phase II for potential commercial uses in such diverse fields as law enforcement, rescue and recovery operations, maritime and aviation collision avoidance sensors, medical uses, homeland defense, and other infrared detection and imaging applications. 

REFERENCES: 

1: J. Nguyen, A. Soibel, D. Z.-Y. Ting, C. J. Hill, M. C. Lee, S. D. Gunapala, Appl. Phys. Lett. 97, 051108, (2010).

2:  M. Razeghi, A. Haddadi, A. M. Hoang, R. Chevallier, S. Adhikary, A. Dehzangi, Proc. SPIE 9819, Infrared Technology and Applications XLII, 981909 (May 20, 2016)

3:  E. A. Plis, T. Schuler-Sandy, D. A. Ramirez, S. Myers, S. Krishna, Electron. Lett., 51, 2009-2010 (2015)

KEYWORDS: Strain Layer Superlattice (SLS), Infrared Detector, Dual Band, Mesa Delineation, Focal Plane Arrays, Antimonide Based Materials, Plasma Etch 

CONTACT(S): 

Neil Baril 

(703) 704-4900 

neil.f.baril.civ@mail.mil 

Sumith Bandara 

(703) 704-1737 

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