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       Four-side buttable CCD arrays in production for WaSP and ZTF at Palomar.
Above: Four-side buttable CCD arrays in production for WaSP and ZTF at Palomar.

Detectors & Instruments

World Record Sensitivity in UV Photon-Counting Large Format Arrays

Using of JPL-invented 2D doping (delta-doping and superlattice-doping), we have made UV detectors with 100% internal quantum efficiency (QE). Novel antireflection coatings and detector-integrated filters implemented on detectors using ALD have produced detectors with tailorable response and high QE in the UV/Optical/NIR spectral ranges. The combination of the 2D-doping and ALD produces imagers with reliable, repeatable, and unprecedentedly high performance.

In 2016, NASA selected Large Ultraviolet Optical IR Surveyor Mission (LUVOIR) and Habitable Exoplanet imager (HabEx) as two of the four mission concepts for further studies in preparation for the next decadal survey to be conducted by the National Research Council. Both LUVOIR and HabEx will require unprecedented large apertures, high throughput, and wide spectral range. High-reflectivity coatings for mirrors and high-performance detectors are of critical importance. The Advanced Detectors, Systems, and Nanoscience Group has been preparing for these challenges. Also, as astrophysics instruments requirements have been trending toward larger focal plane arrays (FPAs), CMOS and CCD industries have moved to larger-diameter wafers. These factors dictated the need for an equipment upgrade at MDL. Professor Jonas Zmuidzinas, JPL Chief Technologist and then MDL Director, advised Shouleh Nikzad, to organize a meeting to hear all of the programmatic and technical pro and con arguments to determine if there was a case for such an investment. Jonas’ advice turned out to be an excellent first step in acquiring the first of its kind 8-inch-diameter wafer capacity silicon molecular-beam epitaxy (MBE). State-of-the-art equipment can help turn good ideas into great products and capabilities. Using this MBE and MDL’s atomic layer deposition (ALD), we have produced high performance deep UV, FUV, and UV/Vis/NIR detectors, and a multitude of visible formats in CMOS, CCD, and avalanche photodiode architectures. We have turned a once small R&D effort into a high-throughput end-to-end post-fabrication processing that can be used for delivering high-performance detectors for large FPAs. Young researchers working with our group are supported to continue their work through fellowships from NASA and other agencies; most notable was a Nancy Grace Roman Fellowship to Dr. Erika Hamden who is now an assistant professor at University of Arizona’s Department of Astronomy.

During the same timespan, results from the Galaxy Evolution Explorer (GALEX) mission presented the need for improved UV sensitivity. GALEX was an orbiting ultraviolet space telescope launched on April 28, 2003, and operated until mid 2013. To meet that need we created a set of imaging arrays with >50% external QE in the FUV using MBE for delta doping and ALD for advanced antireflection coatings. This QE is about an order of magnitude higher than the detector onboard GALEX and sets an unprecedented high sensitivity (> 50% QE) in this very challenging part of the spectrum (120-300 nm). We have applied the same technology to various spectral ranges with record sensitivity, for example, in collaboration with Caltech and Columbia University, we demonstrated 80% QE in a photon counting CCD. We have had breakthroughs in developing solar-blind silicon detectors, ultra-stable deep UV detectors, and novel UV imaging spectrometers. MDL detectors are used in synchrotrons, in semiconductor fabrication, in sounding rockets, at Palomar Observatory and Steward Observatory, have flown in a stratospheric balloon flight, are in preparation for CubeSats, and are baselined for several satellite missions. Spinoff developments have led to producing high-reflectivity UV mirror and grating coatings.

        The following pictorial diagram shows the arc of our detector development over the course of past, present, and future flight missions.
The following pictorial diagram shows the arc of our detector development over the course of past, present, and future flight missions.
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