UV Sensitive very high PDE SiPMs with very low X-talk

1. UV Sensitive very high PDE SiPMs with very low X-talk Razmik Mirzoyan1, Pavel Buzhan2, Boris Dolgoshein2, Elena Popova2, Masahiro Teshima1 1- Max-Planck-Institute for Physics, Munich, Germany 2- National Research Nuclear University MEPhI, Moscow, Russia

2. MEPhI - MPI for Physics R&D collaboration and cooperation with PerkinElmer Industries (now EXCELITAS) Developing UV sensitive SiPMs with extremely high PDE, Extremely low crosstalk and low dark rate SiPM Sizes 1x1 and 3x3 mm² µ-cell pitch 50 and 100 µm Geom. Eff. 40-80% Pioneer and great Leader: Prof., member of Russian Academy of Sciences Boris Dolgoshein 1930-2010 B. Dolgoshein, R. Mirzoyan, E. Popova, P. Buzhan, PEI, et al.,

3. Current status of SiPM • Currently there is a lot of enthusiasm about the new devices but the deep understanding is not simple, it comes only slowly • One of the main problems of SiPMs is its low PDE, that is not easy to measure. It shall be disentangled from the cross-talk and after-pulsing. • The after-pulsing in PMTs is a ~1% effect on single ph.e. level, while for example, for currently existing MPPC’s from Hamamatsu it is a 20-30 % (depending on type and the applied over-voltage) effect. • Often the real value of PDE is significantly lower than the claimed (advertised) one. The reasons are a) the low applied overvoltage, b) neglecting of the cross-talk (X-talk) and c) of the after-pulsing. R. Mirzoyan: UV sensitive high PDE, low X-talk SiPM

4. Still trying to understand The PDE of a SiPM can be presented as PDE(l) = Geiger-eff. x Geometry-eff. x Internal-QE x Transmission(l) Geiger-eff. = Function (applied-over-voltage); when Geiger-eff. saturates, one can obtain stable operation, also in the sense of temperature R. Mirzoyan: UV sensitive high PDE, low X-talk SiPM

5. A PDE and gain of a 1x1 mm² SiPM test-sample produced by MEPhI-MPI cooperation; @+20°C Overvoltage = operational voltage – breakdown voltage (~31.5V) • As one can see on the right top the PDE of SiPM saturates at an over-voltage DV/V ~15 % • For higher applied • DV/V the gain (and the noise) will still increase but there will be no further increase of PDE • Hamamatsu MPPCs operate at maximum • DV/V < 3 % Overvoltage +20 % Overvoltage +15 % Overvoltage +10 % Overvoltage + 5 % R. Mirzoyan: UV sensitive high PDE, low X-talk SiPM

6. Optical X-talk and afterpulsing and PDE • We need to learn how to • disentangle the X-talk • and the after-pulsing from • the genuine PDE. • One can see on the right • that depending on the PDE • measuring method, the • X-talk and afterpulsing • contributions together • could be as big as the • PDE by itself. R. Mirzoyan: UV sensitive high PDE, low X-talk SiPM

7. Checking the universality of light emission (the culprit for X-talk) from different SiPM samples • We measured the absolute light emission of an MPPC of 3mmx3mm size from Hamamatsu and of 3mmx3mm and 1mmx1mm size SiPM test-samples from MEPhI-MPI design • As one would expect within errors all three samples emit the same light, the same spectrum R. Mirzoyan: UV sensitive high PDE, low X-talk SiPM

8. Entire light emission spectrum of SiPM Mirzoyan, et al., NIM A 610, 2009 R. Mirzoyan: UV sensitive high PDE, low X-talk SiPM

9. X-talk suppression is improving the performance • Known ways to • suppress X-talk: • trenches • 2nd junction • for isolating the • bulk from the • active region • new method, • shown on right  • d) special coatings (Patent pending) R. Mirzoyan: UV sensitive high PDE, low X-talk SiPM

10. P. Buzhan, B. Dolgoshein, et al., NIM A 610, 2009 R. Mirzoyan: UV sensitive high PDE, low X-talk SiPM

11. Ideal SiPM: a good wish or a reality, where are we ? Operating SiPM @ DV/V ~ 15 % Gain ≤ few x 106 Peak PDE ~ 60 – 65 % High PDE also in near UV (> 50 %) Timing ≤100 ps X-talk ≤ 1-2 % F-factor ≤ 1.02 After-pulsing ≤ 1-2 % Dark rate ≤ 0.5 MHz/mm² (room T°) Size1-10 mm² Low T ° dependence of gain, of PDE Scalable matrixes Signal processing on rear side R. Mirzoyan: UV sensitive high PDE, low X-talk SiPM

12. Improved SiPMs • 18 different variations of SiPM (p over n) have been produced by MEPhI-MPI cooperation (with the support of PerkinElmer, now Excelitas) • Many innovative ideas were implemented R. Mirzoyan: UV sensitive high PDE, low X-talk SiPM

13. Gain linearity Over-voltage, V R. Mirzoyan: UV sensitive high PDE, low X-talk SiPM

14. X-talk for 1mmx1mm SiPM R. Mirzoyan: UV sensitive high PDE, low X-talk SiPM

15. PDE for 1mmx1mm SiPM • When DV/V is set to • ~15 %, the Geiger efficiency • is saturated • As a result dependence • on T ° becomes very low, • it can be as low as • 0.5 %/ °C R. Mirzoyan: UV sensitive high PDE, low X-talk SiPM

16. Conclusions • In a time scale of 1-2 years from now one can buy SiPMs with really outstanding characteristics, probably from several manufacturers. • Their sizes could span 1-10 mm (in remote future perhaps even larger) • SiPM cost will be reduced due to the availability of full CMOS designs. Several USD per mm² is not very unrealistic. • These devices are going to substitute classical PMTs and APD in many (but of course not all) applications, including those in physics instrumentation in, for example, nuclear medicine (time-of-flight PET,…). • We could demonstrate samples with max. PDE of 50-60 %, X-talk in the range of < 2-5 % and a very high PDE also in the UV when operated at ~15 % over-voltage R. Mirzoyan: UV sensitive high PDE, low X-talk SiPM

17. Reminder: light absorption in Si • Absorption of light in Si • Already from this graph • one can get an impression • about the relevant for the • X-talk effect • wavelength range • Absorption length below • ~370 nm is below 10 nm R. Mirzoyan: UV sensitive high PDE, low X-talk SiPM