Silicon Photomultiplier Performance
PDE measurements of Sensl 1mm devices (E. Smith)
The following numbers are taken from the first two rows of Zisis talk at the collaboration meeting (p 5, 1x1 mm2 SiPM parameters)
| Design | Pixels | DR @ 4V | Fill Factor | Dark Current | Peak PDE @ 4V |
|---|---|---|---|---|---|
| (MHz) | (%) | (μA) | (%) | ||
| C20 | 620 | 2.9 | 17 | -2 | 8.5 |
| A20L | 920 | 5.9 | 34 | -3 | 17.0 |
From Carl's talk (p 37, QE and PDE), you can determine the ratio of the PDE@4V to PDE@1.2V, which was the chosen operating point for Carl's measurements. The ratio is approximately 2. Therefore, the expected PDE@1.2V for the C20 is about 8.5/2 = 4.2. Carl measured it to be 4.4 ± 0.5.
Conclusion: At the operating point of about 1.2 V above breakdown, the PDE for the C20 (1mm2, 17% fill factor) SiPM is about 4.5%. So far, our experience tells us that the practical operating point for these devices is about 1V over voltage. As the voltage above the breakdown increases further signal to noise decreases and even pulse shape become distorted.
If we use the A20L instead of the C20, the PDE will double, but so will the dark rate. We believe that the estimated 110 MHz rate for the 4x4 array is for the 1V over voltage, thereby consistent with a PDE of 4.5%.
Comments are welcome. In particular, it would be useful for Richard to remind us the conditions that were used for his measurements of the PDE for the 1x1 and 2x2 mm2 SiPMs.
PDE measurements of Photonique SiPM devices (R. Jones)
The following numbers are taken from the report gluex-doc-760. They are consistent with the data sheets for these devices available on the photonique web site. The SSPM_050701GR_TO18 SiPM (first row in the table) is the 1 mm2 device. It has a slightly higher peak PDE at 600 nm than the newer 4.4 mm2 device (second row in the table) but, but the larger SiPM efficiency drops off more slowly at shorter wavelengths and so it is actually more efficient in the green-blue region.
| Device | Pixels | DR @ 1.5V | Peak PDE | PDE(500nm) |
|---|---|---|---|---|
| (MHz) | @ 1.5V (%) | @ 1.5V (%) | ||
| SSPM_050701GR_TO18 | 556 | 9.8 | 30 | 18 |
| SSPM_0606BG4MM_PCB | 1700 | 8.9 | 27 | 24 |
The above PDE values are for T=+22° and 1.5V over the avalanche threshold. Measurements performed on the bench at Connecticut have confirmed the manufacturer's PDE values at 570 nm, the wavelength of the yellow LED we used for these tests.
If one wants to compare the Sensl and Photonique devices, it is only fair to compare them under the same operating conditions: 1.5V over threshold. From Carl's measurements, the actual efficiency of the Sensl C20 device is about 5% compared with 24% for the 2 mm Photonique device under the same conditions. The factor of 5 in PDE between the Sensl and Photonique devices can only be explained by the supposition that Sensl never intended their C20 device to be considered for scintillator readout. Nor should 12% @ 500 nm be considered acceptable, given that commercial devices from Photonique exist with a factor 2 larger PDE. We have heard that CPTA technology is primitive, and that may be so, but then it should not be difficult to reproduce their performance in these new devices from Sensl.
