Advanced Detectors, Systems, & Nanoscience
Atomic Layer Deposition (ALD) for Detector, Optics, and Filters Fabrication and Enhancement
Atomic layer deposition is a thin-film deposition technique where a desired film is grown using sequential surface reactions, one monolayer at a time. The properties inherent to the ALD method enable growth of high-quality, smooth, dense, pin-hole-free films with precise, angstrom-level thickness control over arbitrarily large surface areas. ALD is also well-suited for the growth of multilayer stacks of films with sharp interfaces. These characteristics of ALD make it ideally suited for fabrication of all types of optical elements, including mirrors, filters, and coatings, with the highest possible performance.
JPL has recently completed the world’s first demonstration of direct integration of ALD-deposited anti-reflection coatings with silicon imagers. ALD of aluminum oxide and hafnium oxide combined with delta doping has produced world-record quantum efficiency in the ultraviolet from 150 nm to 300 nm. Future work in this area will be used to expand the range of ALD AR coatings both farther into the UV and into the visible. JPL has also dramatically improved the performance of FUV indium-based filters, more than doubling their transmission. This new JPL technology will enable a University of Colorado rocket flight to image a spectral region hitherto unexplored astronomically, potentially leading to the discovery of new quasars and development of new stellar evolution models.
In addition to ALD’s applications for optical coatings, it is an excellent material for passivation of III-N materials. JPL is fabricating III-N pin diode arrays and III-N APDs for solar-blind and radiation-tolerant detection of UV for planetary observation and has obtained extremely low leakage (often below the detection limit of nA). Atomic layer deposition is expected to provide even better performance and enhance the stability of these detectors.