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Register a new userFirst tests and long-term prospects of Geigermode avalanche photodiodes as camera sensors for IACTs
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Authors
Eckart Lorenz
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Geigermode avalanche photodiodes (G-APD) are novel photodetectors, which can detect single photons. This type of diodes might become an alternative to photomultipliers (PMT) in next-generation Imaging Air Cherenkov Telescopes. Prospects, limitations and development directions are be discussed. Results from first tests are reported.
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In October 2013, the Italian Ministry approved the funding of a Research & Development (R&D) study, within the Progetto Premiale TElescopi CHErenkov made in Italy (TECHE), devoted to the development of a demonstrator for a camera for the Cherenkov Telescope Array (CTA) consortium. The demonstrator consists of a sensor plane based on the Silicon Photomultiplier (SiPM) technology and on an electronics designed for signal sampling. Preliminary tests on a matrix of sensors produced by the Fondazione Bruno Kessler (FBK-Trento, Italy) and on electronic prototypes produced by SITAEL S.p.A. will be presented. In particular, we used different designs of the electronics in order to optimize the output signals in terms of tail cancellation. This is crucial for applications where a high background is expected, as for the CTA experiment.
Optical intensity interferometry, developed in the 1950s, is a simple and inexpensive method for achieving angular resolutions on microarcsecond scales. Its low sensitivity has limited intensity interferometric observations to bright stars so far. Substantial improvements are possible by using avalanche photodiodes (APDs) as light detectors. Several recent experiments used APDs in single-photon detection mode; however, these either provide low electronic bandwidths (few MHz) or require very narrow optical bandpasses. We present here the results of laboratory measurements with a prototype astronomical intensity interferometer using two APDs observing an artificial star in continuous (linear) detection mode with an electronic bandwidth of 100~MHz. We find a photon--photon correlation of about $10^{-6}$, as expected from the ratio of the coherence times of the light source and the detectors. In a configuration where both detectors are on the optical axis (zero baseline), we achieve a signal-to-noise ratio of $sim$2700 after 10 minutes of integration. When measuring the correlation as a function of baseline, we find a Gaussian correlation profile with a standard deviation corresponding to an angular half-width of the artificial star of $0.55$, in agreement with the estimate by the manufacturer. Our results demonstrate the possibility to construct large astronomical intensity interferometers using linear-mode APDs.
The upgrades of ATLAS and CMS for the High Luminosity LHC (HL-LHC) highlighted physics objects timing as a tool to resolve primary interactions within a bunch crossing. Since the expected pile-up is around 200, with an r.m.s. time spread of 180 ps, a time resolution of about 30 ps is needed. The timing detectors will experience a 1-MeV neutron equivalent fluence of about $Phi_{eq}=10^{14}$ and $10^{15}$ cm$^{-2}$ for the barrel and end-cap regions, respectively. In this contribution, deep diffused Avalanche Photo Diodes (APDs) produced by Radiation Monitoring Devices are examined as candidate timing detectors for HL-LHC applications. To improve the detectors timing performance, the APDs are used to directly detect the traversing particles, without a radiator medium where light is produced. Devices with an active area of $8times8$ mm$^2$ were characterized in beam tests. The timing performance and signal properties were measured as a function of position on the detector using a beam telescope and a microchannel plate photomultiplier (MCP-PMT). Devices with an active area of $2times2$ mm$^2$ were used to determine the effects of radiation damage and characterized using a ps pulsed laser. These detectors were irradiated with neutrons up to $Phi_{eq}=10^{15}$ cm$^{-2}$.
Modern avalanche photodiodes (APDs) with high gain are good device candidates for light readout from detectors applied in relativistic heavy ion collisions experiments. The results of the investigations of the APDs properties from Zecotek, Ketek and Hamamatsu manufacturers after irradiation using secondary neutrons from cyclotron facility U120M at NPI of ASCR in v{R}ev{z} are presented. The results of the investigations can be used for the design of the detectors for the experiments at NICA and FAIR.
Avalanche photodiodes (APDs) are the semiconducting analogue of photomultiplier tubes offering very high internal current gain and fast response. APDs are interesting for a wide range of applications in communications1, laser ranging2, biological imaging3, and medical imaging4 where they offer speed and sensitivity superior to those of classical p-n junction-based photodetectors. The APD principle of operation is based on photocurrent multiplication through impact ionization in reverse-biased p-n junctions. APDs can either operate in proportional mode, where the bias voltage is below breakdown, or in Geiger mode, where the bias voltage is above breakdown. In proportional mode, the multiplication gain is finite, thus allowing for photon energy discrimination, while in Geiger mode of operation the multiplication gain is virtually infinite and a self-sustaining avalanche may be triggered, thus allowing detection of single photons5. Here, we demonstrate APDs based on vertically stacked monolayer MoS2 and p-Si, forming an abrupt p-n heterojunction. With this device, we demonstrate carrier multiplication exceeding 1000. Even though such multiplication factors in APDs are commonly accompanied by high noise, our devices show extremely low noise levels comparable with those in regular photodiodes. These heterostructures allow the realization of simple and inexpensive high-performance and low-noise photon counters based on transition metal dichalcogenides.
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