Study of MPPC at liquid nitrogen temperature

1. Study of MPPC at liquid nitrogen temperature 27/Jun/2007 International Workshop on new photon-detectors ICEPP , University of Tokyo Hidetoshi Otono, Satoru Yamashita, Tamaki Yoshioka, Hideyuki Oide, Hitoshi Hano, Toru Suehiro On behalf of the KEK Detector Technology Project

2. Introduction MPPC and other Geiger-mode APD integrated quenching register are expected to be useful at low temperatures for several purpose. • Noise reduction • Use w/ liquid inorganic scintillators • LiAr (-183℃) • LiXe(-110℃) • Use in outer space for astrophysics • Our measurement Temp. • 300K : Room Temp. • 201K : Ethanol / Dry ice • 77K : LiN2 Temp. LiN Temp. (77K) Ethanol / Dry ice (201K) Room Temp. (300K) Outer Space Temp. (200K~) LiAr Temp. (90K) LiXe Temp. (163K)

3. Setup These components are directly cooled by LiN and Ethanol / Dry ice LiN or Ethanol / Dry ice -Voltage [V] Electronics • Topics • Waveform • Gain • Breakdown Voltage • Noise Rate • Cross-talk • After-pulse 1600 pixel MPPC

4. Waveform Fast / Slow component can be clearly seen in LiN Temp. Slow component depends on temperature very much. It is due to variation of RC time constant Pulse Shape in 300K Pulse Shape in201K Pulse Shape in 77K

5. Variation of quenching register value Quenching registers are made of poly-silicon Current [mV] +Voltage [V] IV curve [mA] Red300K Green201K Blue77K [V]

6. Variation of capacitance of p-n junction Gain[10 ] 5 d ADC Clock ADC Dist.@ Self trigger MPPC AMP Disc. Red300K Green201K Blue77K ADC Dist.@ Random trigger Vop [V] Capacitance is about the same

7. 5ns Pulse Shape in 300K 40ns 10ns Pulse Shape in201K Pulse Shape in 77K

8. 5 Gain[10 ] Breakdown Voltage [V] Vop [V] Red300K Green201K Blue77K 50mV / ℃ Temp. Linear correlation can be seen at low temperatures.

9. Dark Noise MPPC AMP Disc. Scaler Noise Rate [Hz] Red300K Green201K Blue77K 5 6 1 2 0 1 Over Voltage [V] Noise Rate is significantly reduced

10. Cross-talk In avalanche process, the secondary photon is emitted and fire another pixel. Because the original pulse and cross-talk pulse output at the same time, we can discriminate Cross-talk by using Disc. We measured probability that normal pulse trigger cross-talk. Prob. Scaler Red300K Green201K Blue77K MPPC AMP Disc.1 Disc.2 Disc1 THR for normal pulse Disc1 THR for cross-talk Over Voltage [V] Cross-talk Prob. is slightly reduced at low temperature

11. After-Pulse In avalanche process, some electrons are trapped and re-emitted after a certain time. We measured re-emission time constant. By using ADC we select normal noise (Not cross-talk) as a original pulse. Original pulse ADC latch Disc. Disc. ADC Clock G.G latch Or. latch TDC G.G latch Delay Disc. MPPC AMP Disc. Disc. TDC Coin. Delay veto

12. Re-emission time constant known [ns] • Re-emission time constant is • elongated at low temperature Vop[V]

13. Recovery in 77K Right after avalanche process, the voltage between p-n junction corresponds to breakdown voltage. By looking at the pulse shape in 77K, we can clearly see the recovery from breakdown voltage to applied voltage. [mV] [ns] But this recovery in 300K is very fast(<10ns), thus it is difficult to see the recovery. Subject of next speaker

14. Summary • We have studied the MPPC basic properties at low temperature. • Waveform At low temperature, quenching register (made of poly-silicon) value become high. Thus slow component of waveform is elongate.(~8 times) • Gain Breakdown voltage is proportional to temperature (~ 50mV / ℃) MPPC’s gain at low temperature is more than 10 . • Dark Noise Noise rate at low temperature is significantly reduced 5 6 1 2 0 1

15. Summary (con’t) • Cross-talk Cross-talk Prob. is slightly reduced at low temperature • After-pulse Re-emission time constant is elongated at low temperature Future work • To measure probability that after-pulse occurs at low temperature Because of the slow recovery of pulse height, we were not able to detect small after-pulse by NIM and CAMAC modules • To measure QE at low temperature

16. backup

17. Probability which after-pulse comes in 50 ns • Entries • Normal Noise • Cross-talk • Accidental Noise • After-pulse known Prob = After-pulse/Entries Prob. Red300K Green201K Blue77K Normal Noise Over Voltage [V]