Radiation Degradation of Photodiodes
Ping-Shine Shaw
Laser Applications Group, NIST
0.16
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
7.5
2
0
5.0
X (mm)
8
6
4
2.5 Y (mm)
0.0
Solar Spectral Irradiance Variations Workshop 02/29/2012
Detector Degradation
How? And Why?
Detectors: Solid state photodiodes, PMT
Low intensity tunable
radiation from 120 to
320 nm for spectral
characterization
Excimer
Laser
Radiation damage study of photodetectors
Pulsed irradiation
at 157 nm with
1mJ/cm2 per shot
SURF III
2-m monochromator
Detector under
test
Detector Radiation Damage by 157 nm Laser
Relative Responsivity at 157 nm
1.2
GaP
1.0
PtSi
0.8
SiC
0.6
S5227
0.4
UVG-100
GaAsP
GaAsP
AXUV100G
0.2
0.0
10
100
1000
10000
Specific Fluence (mJ/cm2)
100000
1000000
Responsivity degradation of a S5227 photodiode
S(H) / S(0) for S5527
1.0
0.9
β = 0.92, k = 0.0005
0.8
0.7
β = 1.40, k = 23.93
0.6
λ = 193 nm
λ = 135 nm
0.5
0.4
0.3
β = 0.81, k = 1.82
0.2
λ = 157 nm
0.1
0.0
10-5
10-4
10-3
10-2
10-1
100
101
Radiant Exposure H (J / cm 2)
102
103
Degradation of a Si photodiode can be modeled
S1337
AXUV-100G
S5227
UVG-100
Spectral responsivity recovery of an S1337 Si photodiode
exposed to 157 nm radiation of 0.8 J/cm2
Before exposure
6 months after
exposure
Right after exposure
What causes Si photodiode to degrade?
Reflected beam
Incident beam
Front Entrance
SiO2 Window
en+ Region
h+
n-Type Silicon
p+ Region
p-Type Silicon
Internal Quantum Efficiency degradation of a Si
photodiode after EUV exposure
Reduction in Internal QE
0
-0.02
-0.04
-0.06
-0.08
-0.1
-0.12
-0.14
300
350
400
450
500
Wavelength (nm)
550
600
Penetration depth of radiation inside silicon substrate
Incident
Radiation
Front Entrance
Window
n+ Region
Penetration depth in Si (nm)
p+ Region
Doped n–Type
Region
p-Type Silicon
10000
1000
100
10
1
200
300
400
500
Wavelength (nm)
600
Comparison of radiation degradation and penetration depth
Relative responsivity
1.00
0.95
0.90
Silicon photodiode damaged
by 157 nm radiation
0.85
0.80
0.75
Penetration depth in Si (nm)
0.70
10000
1000
Penetration depth in silicon
100
10
1
200
300
400
500
600
Wavelength (nm)
Radiation causes changes near the interface (trap states) between
the front window and silicon substrate.
Detector Radiation Damage by 157 nm Laser
Modification of front window strengthens radiation hardness
Relative Responsivity at 157 nm
1.2
GaP
1.0
PtSi
0.8
SiC
0.6
S5227
0.4
UVG-100
GaAsP
GaAsP
AXUV100G
0.2
0.0
10
100
1000
10000
Specific Fluence (mJ/cm2)
100000
1000000
Responsivity and reflectance of a Si photodiode with PtSi window
Internal QE (electrons/photon)
Internal Quantum Efficiency of
a pristine Si Photodiode with PtSi Front Window
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
200
300
400
500
600
Wavelength (nm)
Substantial recombination of electron-hole pair near interface.
Summary
1. Degradation of a silicon photodiode depends on the
wavelength the photodiode exposed to.
2. After exposure to radiation, the spectral responsivity
of a silicon photodiode decreases in the short
wavelengths but not in the long wavelengths.
3. Partial responsivity recovery of a degraded silicon
can occur over a long time.
4. Similarity between the change in spectral
responsivity and penetration depth indicates that Si
photodiode degradation is caused by radiation
induced trap states near front window interface.
Silicon Photodiodes
1.
2.
3.
4.
5.
Wide spectral range (EUV to NIR)
Large active area
Good spatial uniformity
Stable in the near UV – NIR
Inexpensive and easy to use
Measured and calculate reflectance from Si photodiodes with
different oxide thickness