Characterization of large area avalanche photodiodes in X-ray and VUV-light detection

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Abstract
The present manuscript summarizes novel studies on the application of large area avalanche photodiodes (LAAPDs) to the detection of X-rays and vacuum ultraviolet (VUV) light. The operational characteristics of four different LAAPDs manufactured by Advanced Photonix Inc., with active areas of 80 and 200 mm^2 were investigated for X-ray detection at room temperature. The best energy resolution was found to be in the 10-18% range for 5.9 keV X-rays. The LAAPD, being compact, simple to operate and with high counting rate capability (up to about 10^5/s), proved to be useful in several applications, such as low-energy X-ray detection, where they can reach better performance than proportional counters. Since X-rays are used as reference in light measurements, the gain non-linearity between 5.9 keV X-rays and light pulses was investigated. The gain ratio between X-rays and VUV light decreases with gain, reaching 10 and 6% variations for VUV light produced in argon (~128 nm) and xenon (~172 nm), respectively, for a gain 200, while for visible light (~635 nm) the variation is lower than 1%. The effect of temperature on the LAAPD performance was investigated. Relative gain variations of about -5% per Celsius degree were observed for the highest gains. The excess noise factor was found to be independent on temperature, being between 1.8 and 2.3 for gains from 50 to 300. The energy resolution is better for decreasing temperatures due mainly to the dark current. LAAPDs were tested under intense magnetic fields up to 5 T, being insensitive when used in X-ray and visible-light detection, while for VUV light a significant amplitude reduction was observed at 5 T.
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