Introduction on SiPM devices Nicoleta Dinu – LAL Groupe Instrumentation Nicoleta Dinu

Many fields of applications require photon detectors: Astroparticle physics (e.g. TOF, Imaging Cherenkov Counters) Nuclear medicine (e.g.  camera for PET system, diagnostic approaches) High energy physics (e.g. ILC calorimetry) Many others ..……… Characteristics to be fulfilled by the photon detector candidate: Highest possible photon detection efficiency (blue –green sensitive) High speed High internal gain Single photon counting resolution Low power consumption Robust, stable, compact Insensitive to magnetic fields Low cost Nicoleta Dinu

A look on photon detectors characteristics VACUUM TECHNOLOGY SOLID-STATE PMT MCP-PMT HPD PN, PIN APD GM-APD Photon detection efficiency Blue 20 % 60 % 50 % 30% Green-yellow 40 % 80-90 % 60-70 % 50% Red  6 % 90-100 % 80 % 40% Timing / 10 ph.e  100 ps  10 ps tens ns few ns tens of ps Gain 106 - 107 3 - 8x103 1  200 105 - 106 Operation voltage 1 kV 3 kV 20 kV 10-100V 100-500V  100 V Operation in the magnetic field  10-3 T Axial magnetic field  2 T Axial magnetic field  4 T No sensitivity Threshold sensitivity (S/N1) 1 ph.e 100 ph.e 10 ph.e Shape characteristics sensible bulky compact sensible, bulky robust, compact, mechanically rugged VACUUM TECHNOLOGY SOLID-STATE PMT MCP-PMT HPD PN, PIN APD GM-APD Photon detection efficiency Blue 20 % 70 % 50 % Green-yellow 40 % 80-90 % 60-70 % Red  6 % 80 % Timing / 10 ph.e  100 ps  10 ps few ns tens of ps Gain 106 - 107 3 - 8x103 1  200 V 105 - 106 Operation voltage 1 kV 3 kV 20 kV 100-500V  100 V Operation in the magnetic field  10-3 T Axial magnetic field  2 T Axial magnetic field  4 T No sensitivity Threshold sensitivity (S/N1) 1 ph.e 100 ph.e 10 ph.e Shape characteristics sensible bulky compact sensible, bulky robust, compact, mechanically rugged

PIN, APD & GM-APD PIN APD GM-APD p-n junction N-Type Silicon Depletion region P+ active area P-N junction edge P+ - Type N – Type Silicon p+-type silicon (substrate) p--type epitaxial layer p+ n+ p-n junction p-n junction, Vbias < VBD p-n junction, Vbias > VBD Gain = M (~ 50-500) - linear mode operation- Gain = 1 Gain → infinite -Geiger-mode operation-

Geiger Mode - APD the p-n junction is biased at Vbias > VBD i = imax current time p+-type silicon (substrate) p--type epitaxial layer p+ n+ t < t0 i = 0 t = t0 carrier initiates the avalanche t0 < t < t1 avalanche spreading t > t1 self-sustaining current (i = imax) to detect a new photon, a quenching mechanism is required current time t0 t1 t2 VBD Vbias V quenching -Vbias Quenching mechanisms Passive quenching: large resistance Active quenching: analog circuit F. Zappa & all, Opt. Eng. J., 35 (1996) 938 S. Cova & all, App. Opt. 35 (1996) 1956

Model of GM – APD & passive quenching (1) Pioneering work done in the 1960 to model micro-plasma instabilities RCA company by J. R. McIntire, IEEE Trans. Electron Devices, ED-13 (1996) 164 Shockley Research Laboratory by R. H. Haitz, J. App.. Phys. Vol. 36, No. 10 (1965) 3123 First order circuit model of the GM-APD with passive quenching Diode Rs – diode series impedance (~ 1 k) Cd – total junction capacitance VBD – breakdown voltage S – random on-off switching of the avalanche discharge Biasing circuit RQ – quenching resistance (> 100 k) Vbias – bias voltage CD RS VBD RQ VBIAS DIODE S

Model of GM – APD & passive quenching (2) OFF condition No charge traversing the breakdown region S – open Cd – charged to Vbias i ~ 0 through Rq ON condition Avalanche discharge triggered by a carrier generated in the breakdown region (e.g. photon or thermal carrier) S – closed Cd discharge to VBD with a time constant Rs x CD Diode current increases to (Vbias – VBD)/RQ (RQ >> Rs) Diode voltage decreases from Vbias to VBD Cd – recharge again to Vbias with a time constant RQ x Cd ready for a new detection DIODE S CD RQ VBIAS RS VBD current imax ~(Vbias – VBD)/RQ time V Vbias VBD t0 t1 t2 time

Standardized output signal From GM-APD to SiPM GM-APD – gives no information on the light intensity Current (a.u.) Time (a.u.) Standardized output signal p+-type silicon (substrate) p--type epitaxial layer p+ n+ Rquenching -Vbias SiPM (proposed by Sadygov and Golovin in the ’90) matrix of tiny pixels in parallel / each pixel = GM-APD + Rquench output signal is proportional to the number of triggered pixels Al ARC -Vbias Back contact p n+  Rquenching h p+ silicon wafer Front contact Out One pixel fired Two pixels fired Three pixels Current (a.u.) Time (a.u.) - Vbias n pixels GM-APD Rquench

There is SiPM a good candidate photon detector? Fast detector: short rise rime (hundreds of ps, determined by the short time required to avalanche spreading) Excellent capability for photon counting & low-light-level detection high internal gain proportional information to the number of incident photons Others interesting features low bias voltage (< 100V) low power consumption insensitive to magnetic fields compact and rugged Some characteristics under study and progressive technological improvement present devices cover only small surfaces (generally 1x 1 mm2, up to 3 x 3 mm2) reduced photon detection efficiency by the geometric fill factor relevant noise temperature dependence of the gain (breakdown voltage) and dark rate low radiation resistance (generation and trapping centers)