1. UV Sensitive very high PDE SiPMs with very low X-talk Razmik Mirzoyan 1, Pavel Buzhan 2, Boris Dolgoshein 2, Elena Popova 2, Masahiro Teshima 1 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., 16-17 February 2011

3. Saturday 11 June 2011, TIPP-2011, Chicago R. Mirzoyan: UV sensitive high PDE, low X-talk SiPM 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.

4. Saturday 11 June 2011, TIPP-2011, Chicago 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( ) = Geiger-eff. x Geometry-eff. x Internal-QE x Transmission( ) Geiger-eff. = Function (applied-over-voltage); when Geiger-eff. saturates, one can obtain stable operation, also in the sense of temperature

5. Saturday 11 June 2011, TIPP-2011, Chicago R. Mirzoyan: UV sensitive high PDE, low X-talk SiPM 5 Overvoltage +15 % Overvoltage +20 % Overvoltage = operational voltage – breakdown voltage (~31.5V) A PDE and gain of a 1x1 mm² SiPM test-sample produced by MEPhI-MPI cooperation; @+20°C As one can see on the right top the PDE of SiPM saturates at an over-voltage  V/V ~15 % For higher applied  V/V the gain (and the noise) will still increase but there will be no further increase of PDE Hamamatsu MPPCs operate at maximum  V/V < 3 % Overvoltage +10 % Overvoltage + 5 %

6. Saturday 11 June 2011, TIPP-2011, Chicago 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.

7. Saturday 11 June 2011, TIPP-2011, Chicago 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

8. Saturday 11 June 2011, TIPP-2011, Chicago R. Mirzoyan: UV sensitive high PDE, low X-talk SiPM 8 Entire light emission spectrum of SiPM Mirzoyan, et al., NIM A 610, 2009

9. Saturday 11 June 2011, TIPP-2011, Chicago R. Mirzoyan: UV sensitive high PDE, low X-talk SiPM 9 (Patent pending) X-talk suppression is improving the performance Known ways to suppress X-talk: a)trenches b)2nd junction for isolating the bulk from the active region c)new method, shown on right  d) special coatings

10. Saturday 11 June 2011, TIPP-2011, Chicago R. Mirzoyan: UV sensitive high PDE, low X-talk SiPM 10 P. Buzhan, B. Dolgoshein, et al., NIM A 610, 2009

11. Saturday 11 June 2011, TIPP-2011, Chicago R. Mirzoyan: UV sensitive high PDE, low X-talk SiPM 11 Operating SiPM @  V/V ~ 15 % Gain ≤ few x 10 6 Peak PDE ~ 60 – 65 % High PDE also in near UV (> 50 %) Timing ≤100 ps X-talk ≤ 1-2 % F-factor ≤ 1.02 Ideal SiPM: a good wish or a reality, where are we ? 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

12. Saturday 11 June 2011, TIPP-2011, Chicago 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

13. Gain linearity Saturday 11 June 2011, TIPP-2011, Chicago R. Mirzoyan: UV sensitive high PDE, low X-talk SiPM 13 Over-voltage, V

14. X-talk for 1mmx1mm SiPM Saturday 11 June 2011, TIPP-2011, Chicago R. Mirzoyan: UV sensitive high PDE, low X-talk SiPM 14

15. Saturday 11 June 2011, TIPP-2011, Chicago R. Mirzoyan: UV sensitive high PDE, low X-talk SiPM 15 When  V/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 PDE for 1mmx1mm SiPM

16. Saturday 11 June 2011, TIPP-2011, Chicago 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

17. Saturday 11 June 2011, TIPP-2011, Chicago 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