Abstract
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.
Highlights
The ultraviolet (UV) spectral range is populated with atomic and molecular lines that are highly relevant for studying planetary bodies, including solar system planets, exoplanets, comets and asteroids as well as stars, supernovae, black holes, galaxies, and the cosmos
Avalanche multiplication has been used in various silicon detector architectures to achieve signal gain, including including avalanche photodiodes (APDs), APD arrays, single photon avalanche avalanche photodiode photodiode (SPAD) arrays, and electron multiplying charge-coupled devices (EMCCDs) [15]
Capable of photon counting operation, the APDs used here are operated in the linear mode and are discussed because their use atosimulation demonstrate detector-integrated visiblethe rejection filters
Summary
The ultraviolet (UV) spectral range is populated with atomic and molecular lines that are highly relevant for studying planetary bodies, including solar system planets, exoplanets, comets and asteroids as well as stars, supernovae, black holes, galaxies, and the cosmos. UV emission lines and bands from H, C, O, N, S, OH and CO; UV absorption lines by CO2 , H2 O, NH3 , N2 ; and UV surface reflectance spectra are all essential for the detection of ice, iron oxides, organics, and other compounds on planetary bodies. All of these are used as diagnostic tools for understanding the nature and habitability of these bodies. Si during the pulsed sequence is shown to greatly impact defect formation and density as well as carrier concentration. Ga pulse (bottom) increases both the free electron concentration concentration as well as marked improvement in the quality of the AlGaN film.
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