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

Abstract

The present manuscript reviews our R&D studies on theapplication of large area avalanche photodiodes (LAAPDs) to thedetection of X-rays and vacuum ultraviolet (VUV) light. Theoperational characteristics of LAAPDs manufactured by AdvancedPhotonix Inc. were investigated for X-ray detection at roomtemperature. The optimum energy resolution obtained in four LAAPDsinvestigated was found to be in the range 10-18% for 5.9 keVX-rays. The observed variations are associated with dark currentdifferences between the several prototypes. LAAPDs have demonstratedhigh counting rate capability (up to about 105/s) and applicabilityin diverse areas, mainly low-energy X-ray detection, whereLAAPDs selected for low dark current may achieve better performancethan proportional counters. LAAPDs were also investigated as VUVphotosensors, presenting advantages compared to photomultipliertubes. X-rays are often used as a reference in light measurements;this may be compromised by the non-linearity between gains measuredfor X-rays and VUV-light. The gain was found to be lower for X-raysthan for VUV light, especially at higher bias voltages. For 5.9 keVX-rays, gain variations of 10% and 6% were measured relative to VUVlight produced in argon ( ∼ 128 nm) and xenon ( ∼ 172 nm) forgains of about 200. The effect of temperature on the LAAPD performancewas investigated for X-ray and VUV-light detection. Gain variations ofmore than -4% per oC were measured for 5.9 keV X-rays for gainsabove 200, while for VUV light variations are larger than -5% peroC. The energy resolution was found to improve with decreasingtemperature, what is mainly attributed to dark current. The excessnoise factor, another contribution to the energy resolution, wasexperimentally determined and found to be independent of temperature,increasing linearly with gain, from 1.8 to 2.3 for a 50-300 gainrange. The LAAPD response under intense magnetic fields up to 5 Teslawas investigated. While for X-ray detection the APD responsepractically does not vary with the magnetic field, for 172 nm VUVlight a significant amplitude reduction of more than 20% wasobserved.