Re: Understanding PDE information

["George Lolos" <George.Lolos@uregina.ca>]

Hi Elton:

I had a long phone discussion with Padraig Hughes who's the project
manager at SensL for GlueX.  One of the things we discussed was the fill
factor.  SensL quotes almost all, if not all, their results at +4V.  So,
their 110 MHz rate is also at +4 V.  By the way, I was informed that the
latest Si treatment they have made SiPM's out of has a DR/pixel of
slightly over 500 Hz which gives in the A20L a DR for 1mm2 SiPM of
better than 3 MHz at +2V.  Yes, there's a confusion throughout the
industry on what to use as a bench mark for volts over breakdown. 
Another issue that is hard to understand is the connection between bias
and gain and bias and PED.  I am expecting some figures from SensL,
however, while DR (dark current actually) rise linearly with +V, the
gain has a week dependence on it while the PDF also increases marginally
due to better avalanche probability.  Thus, I don't understand the
comment of such decreasing PDE from +4V to +1.2V Carl used.

These are technical points of relevance to direct to SensL next week. 
By the way, the configuration they are pursuing for us is A20H that will
have a PDE of 13.5% but I don't know the bias.

Cheers,

George



>>> Elton Smith <elton@jlab.org> 04/17/07 12:36 PM >>>

Understanding PDE information
-----------------------------

Elke, Carl and I went over the information we have on the SiPM photon
detection efficiency. We believe now that we understand the various
pieces
of information and they are consistent. Let me start with 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
                  (MHz)      (%)         (muA)         @4V (%)
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 110MHz 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.

Cheers, Elton.

Elton Smith
Jefferson Lab MS 12H5
12000 Jefferson Ave
Suite # 16
Newport News, VA 23606
elton@jlab.org
(757) 269-7625