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Avalanche Photodiodes from the Start. R. Rusack The University of Minnesota. Early History. Avalanche Photodiodes were invented by R. McIntyre at RCA in Canada in the late sixties. First considered in HEP at an Isabel meeting. - PowerPoint PPT Presentation
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Snowmass 2001 1
Avalanche Photodiodes
from the Start.R. Rusack
The University of Minnesota
Snowmass 2001 2
Early History
•Avalanche Photodiodes were invented by R. McIntyre at RCA in Canada in the late sixties.
•First considered in HEP at an Isabel meeting.
•Considered at the SDC for the readout of the EM shower max detector.•RCA ( GE EG&G) •API•RMD
Snowmass 2001 3
How they work
+
-
h+
eSi
Ar coating
Contact layer
Collection Region
Avalanche region
Drift
Substrate
Contact layer
Electric Field
p
n
n++
Electrons generated by the incident light are multiplied in the high field region at the junction.
Snowmass 2001 4
Why CMS selected APD’s
Snowmass 2001 6
APD’s with crystals
High side tail suppressed by APD.
Snowmass 2001 7
APD’s in the CMS detector
PbWO4 crystal
Snowmass 2001 8
Light Output from PbWO4
0
20
40
60
80
100
350 400 450 500 550 600 650
Wavelength (nm)
Rel
ativ
e ap
litu
de(%
)
Output is peaked at 420 nm.
~50 photons/MeV from the
Light out from Bogorodisk PbWO4 crystal.
Snowmass 2001 9
APD’s for CMS
Manufacturer:•Hamamatsu Photonics, Japan.
Quantity:•Two APD’s per crystal– 124,000 APD’s
with spares.
Accessibility during operation:•None.
Radiation levels:•Maximum expected dose 200 kGy and
2 1013 neutrons/cm2.
Crystal Light Outout:•~ 50 photons/MeV on a 4.5 cm2 area.
Snowmass 2001 10
Basic APD Structure:
APD is grown epitaxially on an n++ wafer.
Junction
Si2N4 AR coating
Groove to minimize
surface leakage current.
5 5 mm2
active area
Snowmass 2001 11
APD properties
Active area 5x5 mm2
Operating voltage (Vr) ~380 V
Capacitance 70 pF
Serial resistance 3
Dark Current <10 nA
Quantum efficiency 72% @ 420 nm
1/M*dM/dV (M=50) 3.3 %
1/M*dM/dT (M=50) -2.3%
Excess Noise Factor (M=50) 2 Distance to break-down (Vb-Vr) 30-40V Effective Thickness (M=50) 5m Gain range up to 1000
Snowmass 2001 12
APD parameters I
APD#303
0.1
1
10
100
1000
10000
0 100 200 300 400 500
Bias [V]
Gai
n
0
10
20
30
40
50
60
0 500 1000 1500 2000
Gain
1/M
*dM
/dV
[%
]
-30
-25
-20
-15
-10
-5
0
0 500 1000 1500 2000Gain
1/M
*dM
/dT
[%
]
Snowmass 2001 13
1
3
5
7
9
11
13
15
0 500 1000 1500 2000
Gain
Exc
ess
Noi
se F
acto
r
APD parameters II
10
100
1000
10000
0 50 100 150 200 250 300 350 400
Voltage [V]
Ca
pa
cit
an
ce
[p
F]
0
10
20
30
40
50
60
70
80
90
100
300 400 500 600 700 800 900 1000Wavelength [nm]
Qu
antu
m E
ffic
ien
cy [
%]
9.25
11.25
13.25
15.25
X distance in mm
9.25
11.25
13.25
15.25
Y distance in mm
0
1´10-7
2´10-7
3´10-7
A
9.25
11.25
13.25
15.25
X distance in mm
Response uniformity at 420 nm.
Quantum Efficiency
Capacitance v Bias
Excess Noise Factor v Gain
Snowmass 2001 14
Problems Solved
Radiation Damage:•Neutron • Ionizing radiation.•API effect.
Quantum efficiency drift.•Change to epoxy
Lifetime:•Failure due to poor surface
connectivity.
Electrical Characteristics.•High Capacitance.
Snowmass 2001 15
Irradiation Tests.
Irradiation with protons:•All irradiation so far has been with an 70
MeV protons beam at PSI – Switzerland.•2 1013 neutrons/cm2 in ~ 1 hour.
Irradiation with gammas.•All irradiation with 60C0 source.
Irradiation with neutrons.•Setting up a Californium source (252Cf) for
irradiation at the University of Minnesota.•2 1013 neutrons/cm2 in ~ 2 days.
Snowmass 2001 16
Device failure
0
5
10
15
20
25
30
35
0 1000 2000 3000 4000 5000 6000 7000 8000Time (s)
Da
rk C
urr
en
t (
A)
Irradiation in a 70 MeV proton beam.
Snowmass 2001 17
Diagnosis
Breakdown at this point when irradiated. High current at the SiO2-
Al interface.
Solution: increase spacing of Al deposit.
n++
nn++
Al SiO2/SiN
p
p++
Snowmass 2001 18
Lessons
To bring a new technology to reality requires:• Time 1987 to 1996.• Early resources. TNLRC/SSC to show viability.
To go from a possibility to an established technology takes:• Time 1996 to 2001.• Resources ~ $500k.• A manufacturer who sees this technology as a future money earner and does not expect to
recover all costs of development from the experiment.
Expect the unexpected.