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

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 LAAPDs manufactured by Advanced Photonix Inc. were investigated for X-ray detection at room temperature. The optimum energy resolution obtained in four investigated LAAPDs with active areas between 80 and 200 mm 2 was found to be in the range 10-18% for 5.9 keV X-rays. The observed variations are associated to the dark current differences between the several LAAPDs. Moreover, the LAAPD simplicity, compact structure, absence of entrance window and high counting rate capability (up to about 10 5 /s) turn it out to be useful in diverse applications, mainly lowenergy X-ray detection, where LAAPDs selected for low dark current are able to achieve better performance than proportional counters. LAAPDs have been also investigated as VUV photosensors, where they present advantages compared to photomultiplier tubes. Since X-rays are used as reference in light measurements, the gain non-linearity between X-rays and VUV-light pulses has been investigated. The ratio between 5.9 keV X-rays and VUV light gains decreases with gain. Variations of 10 and 6% were observed for VUV light produced in argon (~128 nm) and xenon (~172 nm) for a gain 200, while for visible light (~635 nm) a variation lower than 1% was measured. The effect of temperature on the LAAPD performance was investigated for X-ray and VUV-light detection. Relative gain variations of about -5% per ºC were observed for the highest gains. The excess noise factor was found to be independent on temperature, presenting values of 1.8 and 2.3 for gains of 50 and 300, respectively. The energy resolution variation with temperature is not related to the excess noise factor, being mainly associated to the dark current. LAAPDs have been tested under intense magnetic fields up to 5 T. Their response in X-ray and visible-light detection practically does not vary with the magnetic field intensity while for 172 nm VUV light a significant amplitude reduction of more than 20% was observed.

Al0.52In0.48P avalanche photodiodes for soft X-ray spectroscopy

“…The Full Width Half Maximum (FWHM) energy resolution of a semiconductor X-ray APD can be expressed as a semi empirical expression from the equations presented in [13,14], given by: …”

Detection of VUV Light with Avalanche Photodiodes

“…When using higher energy X-rays, significantly higher gain reductions were measured, e.g. [41]. In addition, non-linear effects increase with increasing avalanche gain, i.e.…”

Improved x-ray detection and particle identification with avalanche photodiodes

“…They provide a compact, robust, magnetic field insensitive solution for light and x-ray detections with gains on the order of 100 and fast response times. [1][2][3][4] Due to this, APDs are extensively used in a large variety of physics, [5][6][7][8] medical, 9 and aerospace applications. 10 We have studied x-rays with energies between 1 and 10 keV and observed two distinct APD responses to monoenergetic x-rays absorbed in different depths inside the APD.…”

“…13 Our x-ray detection setup consists of two linear arrays of 10 LAAPDs each, in which each LAAPD is mounted on a separate titanium piece for efficient cooling and easy replacement. 3,13 The detector arrays are mounted inside a vacuum around 10 −5 hPa and inside a 5 Tesla magnetic field, above and below the x-ray source. Custom-built low-noise, fast response preamplifiers are fitted to the LAAPDs.…”

“…Both LAAPD/preamplifier assemblies are cooled using an external ethanol circulation system and are actively temperature stabilized at around −30 on their operating temperature. 3,13 Bias voltages were chosen to provide the best energy resolution per APD and ranged from 1.61 kV up to 1.69 kV, approximately 50 V below the breakdown voltage. The pre-amplifiers with two bipolar input transistors in cascode configuration (BFR 182 npn, BFT 92 pnp) have been used for the generation of a fast response from the large capacitance (120 pF) of the LAAPD.…”