Prospects to Use Silicon Photomultipliers for the Astroparticle

Prospects to Use Silicon Photomultipliers for the Astroparticle Physics Experiments EUSO and MAGIC A. Nepomuk Otte Max-Planck-Institut für Physik München

Outline • • • A. Nepomuk Otte EUSO & MAGIC Why new photon detectors? Photon detector requirements The Si. PM principle Development @ MEPh. I and Pulsar Development @ HLL in Munich MPI für Physik 2

Extreme Universe Space Observatory http: //www. euso-mission. org/ A. Nepomuk Otte MPI für Physik 3

Major Atmospheric Gamma Imaging Cherenkov Telescope Gamma ray Particle shower ~ 1 o Che ren k ov l igh t ~ 10 km ~ 120 m http: //hegra 1. mppmu. mpg. de/MAGICWeb/ A. Nepomuk Otte MPI für Physik 4

Motivation for new Photon Sensors Photon detection efficiency (PDE) of state of the art photomultiplier tubes ≈20% A higher PDE results in a better signal to noise ratio (SNR) ≈ 80% PDE improves SNR by a factor 2… 3 Same effect as increasing the MAGIC mirror from 17 m diameter to 70 m Both experiments can lower their energy threshold with more sensitive sensors A. Nepomuk Otte MPI für Physik 5

What is gained by a lower Threshold? MAGIC EUSO • access to lower γ-energies • extend accessible energy range → deeper look into the universe (higher redshifts) → new sources →Egret 280 sources with 0. 1 m² active detector area (<10 Ge. V) →ACT‘s 15 sources with 5 • 104 m² active detector area (>300 Ge. V) A. Nepomuk Otte – overlap with existing experiments AUGER, AGASA, HIRES • detailed study of GZK cutoff • improved energy resolution MPI für Physik 6

Photon Detector Requirements sensitive range [nm] sensor size [mm²] single photon counting dynamic range per sensor [phe] max. dark noise per pixel [1/s] rate capability per pixel [1/s] detection efficiency radiation hardness EUSO 330… 400 4 x 4 yes 100 104 105 >50% yes MAGIC 300… 600 30 x 30 yes 1000 107 108 >20% no most requirements are similar large differences in sensitive range and pixel size challenging: detection efficiency A. Nepomuk Otte MPI für Physik 7

The Silicon Photomultiplier An avalanche photodiode (APD) in Geiger mode is a high efficient single photon counting device A. Nepomuk Otte MPI für Physik 8

The Silicon Photomultiplier An avalanche photodiode (APD) in Geiger mode is a high efficient single photon counting device BUT: Output signal of a single Geiger APD is independent of number of photoelectrons A. Nepomuk Otte MPI für Physik 9

The Silicon Photomultiplier An avalanche photodiode (APD) in Geiger mode is a high efficient single photon counting device … BUT: Output signal of a single Geiger APD is independent of number of photoelectrons Solution: Combine an array of small Geiger APDs onto the same substrate (less then 1 photon per cell) A. Nepomuk Otte MPI für Physik 10

Development @ MEPh. I and Pulsar Enterprize 1 mm P. Buzhan et al. http: //www. slac-stanford. edu/pubs/icfa/fall 01. html 1 mm about 20% active area limits photon detection efficiency A. Nepomuk Otte MPI für Physik 11

Characteristics characteristics of current prototypes: geometry: 24 x 24 pixels = 576 pixels within 1 mm 2 available up to 1024 pixels / mm² Operating voltage: 50 V to 58 V Gain: 105 up to ~ 5 • 106 single pixel time resolution: 570 ps FWHM single pixel recovery time: 1μs dark count rate: 106 counts per second at room temperature A. Nepomuk Otte MPI für Physik 12

R&D Goals to improve existing MEPh. I -Pulsar Prototypes Luminescence of hot avalanche electrons gives rise to crosstalk with neighboring APD cells (40% @ Gain 106) Counter measures: • grooves between pixels to absorb photons • reduce gain (4% Crosstalk @ Gain 105) Photon detection efficiency determined by: • Intrinsic QE • packing density of pixels • Geiger breakdown probability • transmittance of entrance window work on: • reduction of dead area • improve blue sensitivity • optimization of entrance window A. Nepomuk Otte MPI für Physik P. Buzhan et al. NIM A 504 (2003) 48 -52 13

Development @ MPI Semiconductor Laboratory in Munich Different approach to increase photon detection efficiency use of back illumination principle → no dead area photon depleted bulk path of the photo electron Si 50µm … 450µm Blow up of one “micro pixel” A. Nepomuk Otte avalanche regions MPI für Physik output 14

Development @ MPI Semiconductor Laboratory in Munich shallow p+ drift path of a photo electron photon n bulk drift rings p+ deep n avalanche region quench resistor output line Simulations are in final stage: • Operating voltage of avalanche region 50 V • Geiger breakdown probability 60%. . . 90% • average drift time differences < 1 ns A. Nepomuk Otte MPI für Physik 15

Summary and Outlook • We investigate the Si. PM as photon detector in MAGIC and EUSO • First Si. PM prototypes are very promising • Si. PM prototypes already usable for some applications (e. g. PET, Tile. Cal for Tesla) • The development is pursued in two different ways -front illumination @ MEPh. I and Pulsar -back illumination @ HLL in Munich • A lot of R&D ahead: increase effective QE up to 70% increase UV sensitivity reduce crosstalk increase Si. PM size A. Nepomuk Otte MPI für Physik 16