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Ultraviolet detection is often required to be made in the presence of a strong background of solar radiation which needs to be suppressed, but materials limitations at these wavelengths can impact both filter and sensor performance. In this work, we explore the use of 1D photonic bandgap structures integrated directly onto a Si sensor that can operate with solar blindness. These filters take advantage of the improved admittance with silicon to significantly improve throughput over conventional stand-alone bandpass filter elements. At far ultraviolet wavelengths these filters require the use of non-absorbing dielectrics such as the metal fluoride materials of MgF_2, AlF_3 and LiF. The latest performance of these 1D multilayer filters on Si photodiodes and CCD imaging sensors is demonstrated. We have also extended these 1D structures to more complex multilayers guided by the design concepts of metamaterials and metatronics, and to 2D patterned plasmonic hole array filters fabricated in aluminum. The performance of sensors and test filter structures is presented with an emphasis on UV throughput.

In this work, we show that the direct integration of ultraviolet metal-dielectric filters with Si sensors can improve throughput over external filter approaches, and yield devices with UV quantum efficiencies greater than 50%, with rejection ratios of visible light greater than 10^3. In order to achieve these efficiencies, two-dimensional doping methods are used to increase the UV sensitivity of back-illuminated Si sensors. Integrated filters are then deposited by a combination of Al evaporation and atomic layer deposition of dielectric spacer layers. At far UV wavelengths these filters require the use of non-absorbing dielectrics, and we have pursued the development of new atomic layer deposition processes for metal fluorides materials of MgF_2, AlF_3 and LiF. The performance of the complete multilayer filters on Si photodiodes and CCD imaging sensors, and the design and fabrication challenges associated with this development are demonstrated. This includes the continued development of deep diffused silicon avalanche photodiodes designed to detect the fast 220 nm emission component of barium fluoride scintillation crystals, while optically rejecting a slower component at 300 nm.

Ultraviolet (UV) studies in astronomy, cosmology, planetary studies, biological and medical applications often require precision detection of faint objects and in many cases require photon-counting detection. We present an overview of two approaches for achieving photon counting in the UV. The first approach involves UV enhancement of photon-counting silicon detectors, including electron multiplying charge-coupled devices and avalanche photodiodes. The approach used here employs molecular beam epitaxy for delta doping and superlattice doping for surface passivation and high UV quantum efficiency. Additional UV enhancements include antireflection (AR) and solar-blind UV bandpass coatings prepared by atomic layer deposition. Quantum efficiency (QE) measurements show QE > 50% in the 100-300 nm range for detectors with simple AR coatings, and QE ≌ 80% at ~206 nm has been shown when more complex AR coatings are used. The second approach is based on avalanche photodiodes in III-nitride materials with high QE and intrinsic solar blindness., (OLD)Applied Quantum Architectures

We present an overview of the detector for the upcoming Faint Intergalactic Red-shifted Emission Balloon (FIREBall-2) experiment, with a particular focus on the development of device-integrated optical coatings and detector quantum efficiency (QE). FIREBall-2 is designed to measure emission from the strong resonance lines of HI, OVI, and CIV, all red-shifted to 195-225 nm window; its detector is a delta-doped electron multiplying charge coupled device (EM-CCD). Delta-doped arrays, invented at JPL, achieve 100% internal QE from the UV through the visible. External losses due to reflection (~70% in some UV regions) can be mitigated with antireflection coatings (ARCs). Using atomic layer deposition (ALD), thin-film optical filters are incorporated with existing detector technologies. ALD offers nanometer-scale control over film thickness and interface quality, allowing for precision growth of multilayer films. Several AR coatings, including single and multi-layer designs, were tested for FIREBall-2. QE measurements match modeled transmittance behavior remarkably well, showing improved performance in the target wavelength range. Also under development are ALD coatings to enhance QE for a variety of spectral regions throughout the UV (90-320 nm) and visible (320-1000 nm) range both for space-based imaging and spectroscopy as well as for ground-based telescopes.