The measurement of the SiPM photon detection efficiency at...
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Fermi National Accelerator Laboratory, October 2006
The measurement of the SiPM photon detection efficiency at ITC-irst
Nicoleta Dinu
INFN – Trento, Italy
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Nicoleta Dinu 2Fermi National Accelerator Laboratory, October 2006
• Photon Detection Efficiency (PDE) of the SiPM
• Experimental methods used for the PDE measurement
• PDE of the first SiPM prototypes developed at ITC-irst
• Summary and outlook
Outline
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Nicoleta Dinu 3Fermi National Accelerator Laboratory, October 2006
Photon detection efficiency of the SiPM
geomtriggeringSiPM PQE εη ××=
1. QE – the quantum efficiency• probability that a photon generate an e/h pair in the active region of the device (e.g. n+/p
junction of a pixel) - wavelength dependent
a) transmission efficiency through ARC b) internal quantum efficiency(ARC = stack of dielectric layers with appropriate thickness and refraction index)
sourcelightbyemitedphotonsofnrrecordedpulsesoutputofnr
. .
=ηTraditional PDE:
PDE of the SiPM:
p+
πpn+
Anti-ReflectiveCoating (ARC)
SiPM pixel
p+
πpn+
ARC
SiPM pixel
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Nicoleta Dinu 4Fermi National Accelerator Laboratory, October 2006
Total area includes dead regions given by:• quenching resistors• trenches• metal layers
Active area: • ∼ 15- 30% of total area
depending of the layout design
(design not in scale)
-VbiasBack contactp+ silicon wafer
Front contact
ppnn++ppππ nn++
Active area
Trenches with Al
Rquenching
hhνν
Photon detection efficiency of the SiPM (cont)2. Ptriggering – the triggering probability (Pt = Pe + Ph - Pe*Ph)
• probability that a carrier (e or h) traversing the high field region triggers an avalanche• Pe & Ph are linked to the impact ionization rates of the electrons and holes
• electrons have higher ionization rates than holes• both electrons and holes ionization rates increase with the electric field (e.g. overvoltage)
3. εgeom – the geometrical efficiency (active area / total area)
SiPM
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Nicoleta Dinu 5Fermi National Accelerator Laboratory, October 2006
The experimental set-up
Halogen white lamp(OSRAM)
Neutral filters(filter transmittance 10%)
Monocromator(Jobin Yvon HR250)
Photodiode (UDT 221)
SiPM + preamplifier
Optometer
Stage with 3D micrometric movement (50µm precision)
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Nicoleta Dinu 6Fermi National Accelerator Laboratory, October 2006
The methods for the PDE measurement
surfaceSiPMtheonphotonsincident
SiPM thebyrecordedphotonsSiPM N
N
=η
surface SiPMthe onphotonsincidentN
reference calibrated detector(photodiode)
hcλΦN mmW
mmsphinc⋅= )
2/(2//. .
SiPMthecorded by photons reN
DC methodqG
IIN
SiPM
darklight
mms phrec ⋅−
=2//..
Pulses counting method
counts/s) (dark - counts/s) (lightNmms phrec
2//..=
1
2
(for low optical power densities)
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Nicoleta Dinu 7Fermi National Accelerator Laboratory, October 2006
1.E+05
1.E+06
1.E+07
1.E+08
1.E+09
1.E+10
1.E+11
1.E+12
300 350 400 450 500 550 600 650 700 750
wavelength (nm)
Nr.
of in
cide
nt p
hoto
ns/ s
/ mm
^2
Set-up calibration
1.E+05
1.E+06
1.E+07
1.E+08
1.E+09
1.E+10
1.E+11
1.E+12
300 350 400 450 500 550 600 650 700 750
wavelength (nm)
Nr.
of in
cide
nt p
hoto
ns/ s
/ mm
^2
0 filter1st filter2nd filter3rd filter1+2 filters calculated1+2+3 filters calculated1+2 filters measured
hcλΦN mmW
mmsphinc⋅= )/(
2
2//. .
)/(
)(
)()/(
2
2 1WA
A
mmmmW
phot
phot
phot RI
A⋅=Φ
no filters
1 filter2 filters3 filters
Photodiode sensibility:• ~ 4 x 107 photons/s/mm2
Calibration method:• light beam without any filter• each filter separately• each filter factor is calculated at all
wavelengths• if 2 or 3 filters are inserted
simultaneously, the optical power density is calculated based on each filter factor determined previously
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Nicoleta Dinu 8Fermi National Accelerator Laboratory, October 2006
1.5V overvoltage: y = 0.0652x + 8772.82.0V overvoltage: y = 0.0844x + 168112.5V overvoltage: y = 0.1109x + 106523.0V overvoltage: y = 0.1261x + 179103.5V overvoltage: y = 0.1461x + 244344.0V overvoltage: y = 0.1674x + 30282
1.0E+04
1.0E+05
1.0E+06
1.0E+07
1.0E+08
1.E+05 1.E+06 1.E+07 1.E+08 1.E+09
incident photons /s/mm^2
reco
rded
pho
tons
/s/m
m^2
2.0V overvoltage: y = 0.0824x + 5054.32.5V overvoltage: y = 0.1004x + 6517.63.0V overvoltage: y = 0.1222x + 4809.33.5V overvoltage: y = 0.1424x + 103324.0V overvoltage: y = 0.1618x + 11199
1.E+04
1.E+05
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1.E+05 1.E+06 1.E+07 1.E+08 1.E+09
incident photons /s/mm^2
reco
rded
pho
tons
/s/m
m^2
PDE @ 550nm – DC & pulses counting methods (1) DC method
device with εgeom ~ 22%
device with εgeom ~ 22%
Pulses counting method
qGII
NSiPM
darklightmms phrec ⋅
−=2//..
counts/s) (dark - counts/s) (lightNmms phrec
2//..=
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Nicoleta Dinu 9Fermi National Accelerator Laboratory, October 2006
PDE @ 550nm – DC & pulses counting methods (2)
Very good agreement in between the DC and counting pulses methodsPDE increases linearly with the overvoltage at least up to 5V overvoltage
0
5
10
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0 1 2 3 4 5
Overvoltage (V)
PDE
@ 5
50nm
(%)
Pulses counting methodDC methodLinear (Pulses counting method)Linear (DC method)
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Nicoleta Dinu 10Fermi National Accelerator Laboratory, October 2006
0
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wavelength (nm)
PDE
%
1.5V overvoltage2.0V overvoltage2.5V overvoltage3.0V overvoltage3.5V overvoltage
0
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wavelengths (nm)
PDE
%
1.5V overvoltage2.0V overvoltage2.5V overvoltage3.0V overvoltage3.5V overvoltage4.0V overvoltage
Photon detection efficiency – DC method device with εgeom ~ 16%
device with εgeom ~ 22%
Maximum PDE in the range 500 ÷ 600 nm
• ~ 16% @ 4V overvoltage for a SiPM of εgeom ~ 22%
For low λ• the PDE is reduced by the Ptriggering
(only holes trigger the avalanche)For high λ
• the PDE is reduced by the QE(QE was optimized for low λ)
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Nicoleta Dinu 11Fermi National Accelerator Laboratory, October 2006
Quantum efficiency
30
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wavelengths (nm)
QE
%
0V-1V-2V-3V-4V-5V
diode with A = 1mm2
30
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wavelengths (nm)
QE
%
0V-1V-2V-3V-4V -5V
diode with A = 0.5625mm2
Diode:• Test structure with the same (n+/p
junction + ARC) as each SiPM pixel• Works as a photodiode at low
reversed bias (0V, 1V or 2V)• Allows the measurement of the QE
(transmission through ARC & internal quantum efficiency)
The impact ionization effect already visible at 3-4V
QE > 95% in the blue region(optimized for λ~ 420nm)
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Nicoleta Dinu 12Fermi National Accelerator Laboratory, October 2006
1.5V overvoltage2.0V overvoltage2.5V overvoltage3.0V overvoltage3.5V overvoltage
0
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wavelengths (nm)
Trig
gerin
g pr
obab
ility
%
0102030405060708090
100
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wavelengths (nm)
Trig
gerin
g pr
obab
ility
%
1.5V overvoltage2.0V overvoltage2.5V overvoltage3.0V overvoltage3.5V overvoltage4.0V overvoltage
Triggering probability
device with εgeom ~ 22%
device with εgeom ~ 16% Calculated from:
geomtriggeringSiPM PQE εη ××=
Only holes trigger the avalanche
Both holes and electrons trigger the avalanche
Only electrons trigger the avalanche
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Nicoleta Dinu 13Fermi National Accelerator Laboratory, October 2006
Light absorption
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0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2depth (um)
Dop
ing
conc
.
0E+00
1E+05
2E+05
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4E+05
5E+05
6E+05
7E+05
E fie
ld (V
/cm
)
DopingField
pn+
h e
At low wavelengths only the holes cross the high field region & trigger the avalanche⇒ triggering probability @ low λ (e.g. 385, 390, 395nm) = hole triggering probability
At high wavelengths only the electrons cross the high field region & trigger the avalanche⇒ triggering probability @ high λ (e.g. 700nm) = electron triggering probability
Simulated doping profile and electric field of the SiPMAttenuation of the light intensity in silicon (Beer-Lambert law)
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Nicoleta Dinu 14Fermi National Accelerator Laboratory, October 2006
0.00
0.20
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Overvoltage (V)
trigg
erin
g pr
obab
ility
hole probability (390nm)hole probability (395nm)electron probability (730nm)Lineare (hole probability (390nm))Lineare (hole probability (395nm))Lineare (electron probability (730nm))
Electron & hole triggering probability
Pholes
Pelectrons
Pe & Ph increase linearly with the overvoltage up to 4VThe slight difference of 0V point could arises from the unavoidable statistical variation of the Vbreakdownacross the structure
Ref. data: W. Oldham & all,• “Triggering phenomena in avalanche
diodes”, IEEE Trans. on Electron Devices Vol. ED-19, No.9, Sept. 1972
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Nicoleta Dinu 15Fermi National Accelerator Laboratory, October 2006
Photon detection efficiency of the SiPM devices developed at ITC-irst
Two experimental methods:• DC & pulses counting• very good agreement in between the two methods (λ=550nm)
Photon detection efficiency:• Depends of three factors:
• geometrical efficiency: ~15-30% (e.g. function of the layout design)• quantum efficiency: > 95% in the blue region (optimized for 420nm)• triggering probability: Pe > Ph
• Maximum in the range 500-600 nm :• ~ 16% @ 4V overvoltage for a device of εgeom= 22%• for low λ it is reduced by the Ptriggering (only holes trigger the avalanche)• for high λ it is reduced by the QE (optimized for blue region)
• Increases linearly with the overvoltage (at least up to 4V overvoltage)
Summary