Back Illuminated Drift Silicon Photomultiplier as Novel Detector for Single Photon CountingChristine Merck, Rouven Eckhardt, Robert Hartmann, Peter Holl, Christian Koitsch, Razmik Mirzoyan, Hans-G unther Moser, Jelena Ninkovic, Rainer H. Richter, Gerhard Schaller, Florian Schopper, Heike Soltau, Lothar Str uder, Masahiro Teshima and George V alceanuAbstractSingle photon counting plays an essential role for a wide variety of applications, ranging from biomedical research to astronomy. In gamma-ray astronomy, the Cherenkov telescope MAGIC is used to detect Cherenkov photons generated in atmo-spheric air showers. Since the flux of Cherenkov photons from air showers is low, the development of new single photon detectorswith high quantum efficiency is necessary. The concept of the Back Illuminated Drift Silicon Photomultiplier (BID SiPM) is a novel detector design for single photon counting. It combines the principles of a silicon photomultiplier (SiPM) and a drift diode. The back illuminated drift silicon photomultiplier is operated asback illuminated detector thus providing a fill factor of 100%. Ahigh quantum efficiency of about 80% in a wavelength region of 300 1000 nm can be achieved. The drift region is used to focus electrons from the back through the depleted bulk to the small point-like avalanche region. The time jitter of the electrons limits the time resolution of the detector to about 1 ns as simulation results show. A prototype of an avalanche region which can be combined with a drift structure was produced at the MPI Semiconductor Laboratory as proof of principle. The detector concept and results of measurements of dark rate and leakage current are presented.Index TermsBID SiPM, Silicon Photomultiplier, AvalancheDiode, Single Photon Counting, High Quantum Efficiency, Back IlluminationI. INTRODUCTION DETECTION of low light fluxes and single photon count- ing is an issue in many experiments ranging from medical research 1 to astronomy 2. The improvement of detectors for single photon counting is therefore of utmost importance. Inground based gamma-ray astronomy, low fluxes of Cherenkov photons are detected by imaging of extended air showers which develop in the atmosphere. Extended air showers are generatedManuscript received November 27, 2006; Christine Merck is with the Max-Planck-Institut f ur Physik, F ohringer Ring 6, 80805 M unchen, Germany and MPI Halbleiterlabor, Otto-Hahn-Ring 6, 81739 M unchen, Germany, Email: cemhll.mpg.de Hans-G unther Moser, Jelena Ninkovic, Rainer H. Richter are with the Max- Planck-Institut f ur Physik, F ohringer Ring 6, 80805 M unchen, Germany and MPI Halbleiterlabor, Otto-Hahn-Ring 6, 81739 M unchen, Germany Rouven Eckhardt, Robert Hartmann, Peter Holl, Christian Koitsch and Heike Soltau are with PNSensor GmbH, R omerstrasse 6, 80803 M unchen, Germany and MPI Halbleiterlabor, Otto-Hahn-Ring 6, 81739 M unchen, Germany Razmik Mirzoyan and Masahiro Teshima are with the Max-Planck-Institut f ur Physik, F ohringer Ring 6, 80805 M unchen, Germany Gerhard Schaller, Florian Schopper, Lothar Str uder and George V alceanu are with the Max-Planck-Institut f ur extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany and MPI Halbleiterlabor, Otto-Hahn-Ring 6, 81739 M unchen, Germanymainly by incident hadrons of cosmic origin 3 and also, a small fraction of air showers is generated by incident gamma- rays and electrons. As a rule of thumb, there is a linear relationship between energy of the primary incident particle and the amount of Cherenkov photons generated 4: The smaller the energy of the incident particle, the smaller the amount of Cherenkov photons produced during shower development. The MAGIC (Major Advanced Gamma - ray Imaging Cherenkov) telescope is currently the worlds largest Cherenkov telescope with a mirror diameter of 17 m 5. In order to lower the energy threshold of the MAGIC telescope and give good overlap of data received with satellites in the range of ca. 10 GeV 6, the development of detectors with highquantum efficiency is necessary to resolve images of showers generated by gamma-rays in the energy range mentioned above. Currently the camera of the MAGIC telescope consists of 600photomultipliers with peak quantum efficiency of ca. 30% at a wavelength of 400 nm 7. Measurements in the range of 90 GeV 15 TeV are successfully performed 8. The spectrum of Cherenkov radiation has the maximum amount of photons emitted in the ultraviolett and blue range. Part of the UV radi- ation is cut off by absorption of the atmosphere for wavelength of less than 300 nm 9. The amount of Cherenkov radiation per unit wavelength decreases with increasing wavelength so that for wavelength of more than 650 nm the light of the night sky (LONS, average rate of 1012photons/m2/s/sr 10)background starts to dominate and the short (1 ns) flashes of Cherenkov radiation cannot be distinguished from LONS. Thus, the requirements