We report on fabrication and photon detection experiments of Nb/Al and Ta/Al superconducting tunnel junctions (STJs).
5-layer STJ thin-films were fabricated using UV photolithography, DC magnetron sputtering, reactive ion etching, and
chemical vapor deposition techniques. STJs with 4 different sizes (20, 40, 60 and 80 μm) were deposited on sapphire
substrates and tested in a two stage adiabatic demagnetization refrigerator with an operating temperature ~ 50 mK.
Photons from different light sources are injected into the junctions via an optical fiber in combination with a
monochromator which can produce photons from 30 nm to 550 nm with 0.1 nm resolution. The junction is read out
through a charge-sensitive preamplifier followed by a shaping stage. We have measured some performance indicators
and quality factors of the junctions from resultant I-V curves.