1. Introduction on SiPM devices
Nicoleta Dinu – LAL Groupe Instrumentation
Nicoleta Dinu

2. Many fields of applications require photon detectors:
Astroparticle physics (e.g. TOF, Imaging Cherenkov Counters)
Nuclear medicine (e.g.  camera for PET system, diagnostic approaches)
High energy physics (e.g. ILC calorimetry)
Many others ..………
Characteristics to be fulfilled by the photon detector candidate:
Highest possible photon detection efficiency
(blue –green sensitive)
High speed
High internal gain
Single photon counting resolution
Low power consumption
Robust, stable, compact
Insensitive to magnetic fields
Low cost
Nicoleta Dinu

3. A look on photon detectors characteristics
VACUUM
TECHNOLOGY
SOLID-STATE
PMT
MCP-PMT
HPD
PN, PIN
APD
GM-APD
Photon detection efficiency
Blue
20 %
60 %
50 %
30%
Green-yellow
40 %
80-90 %
60-70 %
50%
Red
 6 % %
80 %
40%
Timing / 10 ph.e
 100 ps
 10 ps
tens ns
few ns
tens of ps
Gain
3 - 8x103 1
 200
Operation voltage
1 kV
3 kV
20 kV
10-100V V
 100 V
Operation in the magnetic field
 10-3 T
Axial magnetic field  2 T
Axial magnetic field  4 T
No sensitivity
Threshold sensitivity (S/N1)
1 ph.e
100 ph.e
10 ph.e
Shape characteristics
sensible
bulky
compact
sensible, bulky
robust, compact, mechanically rugged
VACUUM
TECHNOLOGY
SOLID-STATE
PMT
MCP-PMT
HPD
PN, PIN
APD
GM-APD
Photon detection efficiency
Blue
20 %
70 %
50 %
Green-yellow
40 %
80-90 %
60-70 %
Red
 6 %
80 %
Timing / 10 ph.e
 100 ps
 10 ps
few ns
tens of ps
Gain
3 - 8x103 1
 200 V
Operation voltage
1 kV
3 kV
20 kV V
 100 V
Operation in the magnetic field
 10-3 T
Axial magnetic field  2 T
Axial magnetic field  4 T
No sensitivity
Threshold sensitivity (S/N1)
1 ph.e
100 ph.e
10 ph.e
Shape characteristics
sensible
bulky
compact
sensible, bulky
robust, compact, mechanically rugged

4. PIN, APD & GM-APD PIN APD GM-APD p-n junction
N-Type Silicon
Depletion region
P+ active area
P-N junction edge
P+ - Type
N – Type Silicon
p+-type silicon (substrate)
p--type epitaxial layer p+ n+
p-n junction
p-n junction, Vbias < VBD
p-n junction, Vbias > VBD
Gain = M (~ )
- linear mode operation-
Gain = 1
Gain → infinite
-Geiger-mode operation-

5. Geiger Mode - APD the p-n junction is biased at Vbias > VBD
i = imax
current
time
p+-type silicon (substrate)
p--type epitaxial layer p+ n+
t < t i = 0
t = t carrier initiates the avalanche
t0 < t < t1 avalanche spreading
t > t self-sustaining current (i = imax)
to detect a new photon, a quenching mechanism is required
current
time t0 t1 t2
VBD
Vbias V
quenching
-Vbias
Quenching mechanisms
Passive quenching: large resistance
Active quenching: analog circuit
F. Zappa & all, Opt. Eng. J., 35 (1996) 938
S. Cova & all, App. Opt. 35 (1996) 1956

6. Model of GM – APD & passive quenching (1)
Pioneering work done in the 1960 to model micro-plasma instabilities
RCA company by J. R. McIntire, IEEE Trans. Electron Devices, ED-13 (1996) 164
Shockley Research Laboratory by R. H. Haitz, J. App.. Phys. Vol. 36, No. 10 (1965) 3123
First order circuit model of the GM-APD with passive quenching
Diode
Rs – diode series impedance (~ 1 k)
Cd – total junction capacitance
VBD – breakdown voltage
S – random on-off switching of the
avalanche discharge
Biasing circuit
RQ – quenching resistance (> 100 k)
Vbias – bias voltage CD RS
VBD RQ
VBIAS
DIODE S

7. Model of GM – APD & passive quenching (2)
OFF condition
No charge traversing the breakdown region
S – open
Cd – charged to Vbias
i ~ 0 through Rq
ON condition
Avalanche discharge triggered by a carrier generated in the breakdown region (e.g. photon or thermal carrier)
S – closed
Cd discharge to VBD with a time constant Rs x CD
Diode current increases to (Vbias – VBD)/RQ (RQ >> Rs)
Diode voltage decreases from Vbias to VBD
Cd – recharge again to Vbias with a
time constant RQ x Cd
ready for a new detection
DIODE S CD RQ
VBIAS RS
VBD
current
imax ~(Vbias – VBD)/RQ
time V
Vbias
VBD t0 t1 t2
time

8. Standardized output signal
From GM-APD to SiPM
GM-APD – gives no information on the light intensity
Current (a.u.)
Time (a.u.)
Standardized output signal
p+-type silicon (substrate)
p--type epitaxial layer p+ n+
Rquenching
-Vbias
SiPM (proposed by Sadygov and Golovin in the ’90)
matrix of tiny pixels in parallel / each pixel = GM-APD + Rquench
output signal is proportional to the number of triggered pixels Al
ARC
-Vbias
Back contact p n+ 
Rquenching h
p+ silicon wafer
Front contact
Out
One pixel
fired
Two pixels fired
Three pixels
Current (a.u.)
Time (a.u.)
- Vbias
n pixels
GM-APD
Rquench

9. There is SiPM a good candidate photon detector?
Fast detector:
short rise rime (hundreds of ps, determined by the short time required to avalanche spreading)
Excellent capability for photon counting & low-light-level detection
high internal gain
proportional information to the number of incident photons
Others interesting features
low bias voltage (< 100V)
low power consumption
insensitive to magnetic fields
compact and rugged
Some characteristics under study and progressive technological improvement
present devices cover only small surfaces (generally 1x 1 mm2, up to 3 x 3 mm2)
reduced photon detection efficiency by the geometric fill factor
relevant noise
temperature dependence of the gain (breakdown voltage) and dark rate
low radiation resistance (generation and trapping centers)