THESIS
2015
xi, 50 pages : illustrations ; 30 cm
Abstract
Ultraviolet (UV) photodetectors working in solar-blind spectrum ranging from 220 to 280
nm with very high sensitivity are of importance for versatile applications, such as flame
detection, missile plume sensing, chemical/biological agents detection, air and water
purification, space-to-space communications, etc. A truly solar-blind UV photodetector
requires strong out-of-band radiation rejection. In this thesis, the research work on a novel
solid-state solar-blind UV detector is presented.
CaS, with a direct bandgap of 5.38eV, should hold a cut-off wavelength at around 230 nm.
Thus, it is expected to be a strong candidate as the active-layer for high performance solar-blind
UV photodiodes. In this study, a seed-layer-assisted growth approach via molecular
beam epitaxy was devel...[
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Ultraviolet (UV) photodetectors working in solar-blind spectrum ranging from 220 to 280
nm with very high sensitivity are of importance for versatile applications, such as flame
detection, missile plume sensing, chemical/biological agents detection, air and water
purification, space-to-space communications, etc. A truly solar-blind UV photodetector
requires strong out-of-band radiation rejection. In this thesis, the research work on a novel
solid-state solar-blind UV detector is presented.
CaS, with a direct bandgap of 5.38eV, should hold a cut-off wavelength at around 230 nm.
Thus, it is expected to be a strong candidate as the active-layer for high performance solar-blind
UV photodiodes. In this study, a seed-layer-assisted growth approach via molecular
beam epitaxy was developed, which was demonstrated to yield Rocksalt CaS thin films with
high crystalline quality on Zincblende GaAs substrates. The developed Au/CaS/GaAs solar-blind
photodiodes were demonstrated to show superior performance in its visible rejection
power of over 5 orders and quantum efficiency as high as 19%. The key contents of this thesis
include the basic working principle of a Schottky-barrier photodiode, the seed-layer-assisted growth approach and the studies of the photoresponse of the developed CaS solar-blind UV
detector system. Also, a prism dispersion method with a compact quartz-based optical setup
was designed and tested. Such a prism dispersion is demonstrated to enjoy close to 3 orders of
rejection power. Finally, the potential of combining the CaS solar-blind UV detector with a
UV band-pass filter and the compact optical setup as a novel flame sensing unit is addressed.
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