Silicon carbide for UV, alpha, beta and X-ray detectors: results and ...

RESMDD06, Florence, 10-13 October 2006
Silicon carbide for UV, alpha,
beta and X-ray detectors: results
and perspectives
Francesco Moscatelli 1,2*
1
CNR- IMM di Bologna, via Gobetti 101, 40129 Bologna, Italy
2
INFN Perugia, via Pascoli 1 06123 Perugia, Italy
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RESMDD06, Florence, 10-13 October 2006
Outline
• Introduction on SiC properties
• α and β SiC detectors
• UV SiC detectors
• X-ray SiC detectors
• Conclusions
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RESMDD06, Florence, 10-13 October 2006
Wide Bandgap
E G
=3.2 eV
Low thermally
generated currents
Room temperature
operation
4
3
2
1
0
SiC properties
E g
λ th
Si
GaAs
4H-SiC
(eV)
E c
(MV/cm)
High Critical Field
E C
= 2 MV/cm
(W/cmK)
V s
(10 7 cm/s)
High thermal
conductivity
High saturation
velocity
v S = 200 μm/ns
High
frequency/speed
devices
Short transit time
Low trapping
probability
High Voltage
devices
High Power
devices
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RESMDD06, Florence, 10-13 October 2006
α and β SiC detectors
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RESMDD06, Florence, 10-13 October 2006
Schottky junctions
• Two samples
irradiated at
3 × 10 15 n cm -2
• Two samples
irradiated at
circular Schottky contact Ni 2
Si
n - , 4H – SiC, 40 ± 2 μm
epitaxial 4H-SiC
n + , 4H – SiC, 360 μm
substrate
7 × 10 15 n cm -2 Ohmic contact - Ti/Pt/Au
From : S. Sciortino et al. “Effects of heavy
proton and neutron irradiations on epitaxial SiC
Schottky diodes”, NIM A 552 (2005) 138-145.
(Technology: Alenia Marconi Systems - Rome)
(SiC wafers: CREE Inc., USA)
(epi:CREE, USA or IKZ, Berlin)
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RESMDD06, Florence, 10-13 October 2006
Schottky - Charge collection with ΜΙPs
Neutron irradiated sample
Collected charges [e - ]
1600
1200
800
400
Schottky diodes
300 e - at 600 V after
7x10 15 n/cm 2 !
0 2 4 6 8
Fluence [10 15 n/cm 2 ]
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RESMDD06, Florence, 10-13 October 2006
Schottky - Charge collection with α
particles: neutron irradiated samples
Fluence
S. Sciortino et al. “Effects of heavy proton and
neutron irradiations on epitaxial SiC Schottky
diodes”, NIM A 552 (2005) 138-145.
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RESMDD06, Florence, 10-13 October 2006
p + /n junction
terminated
Ti/Al
p +
4 x 10 19 cm -3 p -
0.4 μm
SiC Process: p + /n
(Technology: IMM-CNR – Bologna, Italy)
(SiC wafers: CREE Inc., USA)
(epi: IKZ, Berlin)
5 x 10 17 cm -3 55 μm
n -
2 x 10 14 cm -3
n +
Ion implantation: Al + @ 300°C
~10 18 cm -3
4H-SiC
Post implantation annealing: 1600°C
Ni
for 30 min 8° offin Argon
Annealing for the contacts: 1000°C for
2 min in vacuum
Area: 0.0078-0.015 cm 2
0.6 μm
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RESMDD06, Florence, 10-13 October 2006
p + n: CC measurements on reference
3000 e - @ 200 V and 3100 e - @ 600 V for diode with D=1 mm*
*F. Moscatelli et al., IEEE Transactions on Nuclear Science
Vol. 53, No. 3 (June, 2006) pp. 1557-1563
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RESMDD06, Florence, 10-13 October 2006
p + n: I - V after irradiation*
Reverse current
density decreases
after irradiation!
Diameter = 1 mm
*F. Moscatelli et al., IEEE Transactions on Nuclear Science
Vol. 53, No. 3 (June, 2006) pp. 1557-1563
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RESMDD06, Florence, 10-13 October 2006
p + n: C-V after irradiation
Capacitance is
constant. The
material turns to
intrinsic
Diameter = 0.4 mm
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RESMDD06, Florence, 10-13 October 2006
Diameter = 1 mm
p + n: CC vs fluence
*F. Moscatelli et al., IEEE Transactions on Nuclear Science
Vol. 53, No. 3 (June, 2006) pp. 1557-1563
• CC is high until
some 10 14 n/cm 2
• CC decreases
sharply after 10 15
n/cm 2 . Only 130
e - after 10 16
n/cm 2* .
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RESMDD06, Florence, 10-13 October 2006
p + n: Annealing analysis
Concentration of some defects produced by
neutrons decreases as a function of the
annealing temperature*. In particular defects:
-E i at E c -0.5 eV (decreases until 400°C then
vanishes)
-Z 1 /Z 2 at E c -0.62 /0.68 eV (decrease until
900°C then vanish)
- Effects on E c -1.16 and E c -1.5 eV?
We want to analyze annealing effects on current
and charge collection
* X. D. Chen et al. JAP 94 (5) pp. 3004-3010, Sep 2003.
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RESMDD06, Florence, 10-13 October 2006
p + n: I-V measurements after 80°C annealing
Average reverse current decreases after annealing at 80°C for
30 minutes and then remains almost constant.
*F. Moscatelli et al, presented at 8 th RD50 Workshop, Prague
June 25-28, 2006.
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RESMDD06, Florence, 10-13 October 2006
p + n: CC measurements after 80°C annealing
After annealing at 80°C the collected charge slightly
increases, in the range of the experimental error.
No recovery of the damage at 80°C (neither at RT!)
*F. Moscatelli et al, presented at 8 th RD50 Workshop, Prague
June 25-28, 2006.
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RESMDD06, Florence, 10-13 October 2006
p + n: I-V and CC after annealing at 200°C
• CC is 2200±50 e - . (Before
annealing CC=1800 e -)
increase of 400 e - of CC.
• J (@ 900 V) is 15 nA/cm 2
(before ann J= 23 nA/cm 2 )
• After an annealing at
200°C for 30 minutes we
have a partial recovery of
the damage.
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RESMDD06, Florence, 10-13 October 2006
p + n: I-V and CC after annealing at 400°C
After 30 min at 400°C the current further decreases and
the CC increases of 40% (from 1400 e - to 1900 e - )
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RESMDD06, Florence, 10-13 October 2006
Ultra-Violet (UV)
and Extreme Ultra-Violet (EUV)
detectors
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RESMDD06, Florence, 10-13 October 2006
QE and responsivity
Quantum efficiency is defined as the number
of carriers generated per incident photon
QE
=η =
J ph
q
Φ
i
J ph = photocurrent density
Responsivity (A/W) is the ratio of the photocurrent to the
incident optical power
Φ i
= incident flux
R
=
J
ph
=
J
ph
q
⋅
q
λ ⋅ =η
q
λ
P
i
Φ
i
hc
hc
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RESMDD06, Florence, 10-13 October 2006
4H-SIC visible blind UV avalanche
photodiode (APD)*
V BD = 96 V
positive temperature
coefficient for
avalanche
breakdown
*F. Yan, Y. Luo, J. H. Zhao and G.H. Olsen,
“4H-SiC visible blind UV avalanche
photodiode”, Electron. Lett. 35, 929 (1999).
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RESMDD06, Florence, 10-13 October 2006
Responsivity of APD*
6H-SiC non-avalanche,
R = 170 mA/W
V = −90V
R max =106 A/W at 270nm,
R drops rapidly with
increasing wavelength and
is comparable to the AC
noise limit at 370nm.
R 270nm /R 370 nm >20
*F. Yan, Y. Luo, J. H. Zhao and G.H. Olsen,
“4H-SiC visible blind UV avalanche
photodiode”, Electron. Lett. 35, 929 (1999).
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RESMDD06, Florence, 10-13 October 2006
Ni/4H-SiC Schottky EUV photodiodes (1)*
I–V measurement
I = 0.1 pA at −4 V
Ideality factor = 1.06.
*Jun Hu et al., OPTICS LETTERS , Vol. 31, No.
11 June 1, 2006
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RESMDD06, Florence, 10-13 October 2006
Ni/4H-SiC Schottky EUV photodiodes (2)*
• QE (0 V) > 50% from 230 to 295
nm, QE= 65% at 275 nm,
(internal QE ≈100%).
• The rejection ratio of UV to
visible light is higher than 1000.
• QE (EUV) > 100% for λ< 50
nm,
• QE (EUV) > 30 e/photon at 3
nm.
*Jun Hu et al., OPTICS LETTERS ,
Vol. 31, No. 11 June 1, 2006
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RESMDD06, Florence, 10-13 October 2006
4H-SiC single photon counting
avalanche photodiode SPAPD(1)*
V br ≈ 78 V.
The peak QE ≈ 20%
for λ= 270 - 280 nm.
The QE ⇓ when λ⇑for
λ>280 nm because of the
indirect bandgap of 4H-
SiC. At 385 nm, the band
edge of 4H-SiC, the photo
current is lower than the
system detection limit.
*X. Xin et al., ELECTRONICS LETTERS
17th February 2005 Vol. 41 No. 4
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RESMDD06, Florence, 10-13 October 2006
4H-SiC SPAPD (2)
At 350 nm QE=1.6%, flux=280
photons/ μs
photon count rate is about 4.5 MHz
(89 signal pulses in 20 μs), n p of
photons absorbed per μsby the SPAD
is 6. The probability for n p to be
counted is 75%
The average photon counting
efficiency is therefore 1.2%.
At the peak λ = 353 nm, the photon
counting efficiency is estimated to be
2.6% (3.5% QE times 75% counting
probability).
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RESMDD06, Florence, 10-13 October 2006
X-ray detectors
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RESMDD06, Florence, 10-13 October 2006
Soft X-ray Absorption length
10mm
Absorption Length, λ
1mm
100µm
10µm
1µm
Diamond
SiC≡Si
SiC = Si
0.1 1 10 30
Photon Energy [ keV ]
λ SiC ≤λ Si
Can SiC compete with Si Si ? (!)
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RESMDD06, Florence, 10-13 October 2006
Electron-hole pairs : Signal !
Semiconductor Semiconductor E GAP GAP
εε
e-h e-h pairs pairs
@ 10 10 keV keV
Ge Ge 0.7 0.7 3.0 3.0 3.3 3.3 k
Si Si 1.1 1.1 3.7 3.7 2.7 2.7 k
GaAs GaAs 1.4 1.4 4.2 4.2 2.4 2.4 k
CdTe CdTe 1.5 1.5 4.5 4.5 2.2 2.2 k
4H-SiC 3.3 3.3 7.8 7.8 1.3 1.3 k
What about the SiC detector noise ?
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RESMDD06, Florence, 10-13 October 2006
Run of SiC X-Ray Detectors
(Technology: Alenia Marconi Systems - Rome)
(SiC wafers: CREE Inc., USA)
Schottky contact - Au
n - epilayer 5x10 14 - 70 μm
n+ buffer 1 μm
n+ substrate - 320 μm
ohmic contact - Ti/Pt/Au
G. Bertuccio, “Prospect for energy resolving X-ray
imaging with compound semiconductor pixel
detectors, NIM A 546 (2005) 232-241
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RESMDD06, Florence, 10-13 October 2006
Leakage Current Density
State of the art detectors
Current density [ A / cm 2 ]
10 -8
10 -10
10 -12
10 -6 10 -14
CdTe
Room Temperature
GaAs (SI LEC)
CdZnTe
Silicon
GaAs (VPE)
200
200
4H-SiC (Epi)
10 -6
Si
1 nA/cm 2
10 -8
SiC
5 pA/cm 2
10 -10
10 -12
10 -14
0,1 1 10 100
Mean electric field [ kV / cm ]
G. Bertuccio et al., IEEE Trans. Nucl. Sci. 50 (2003), pp. 175-185
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RESMDD06, Florence, 10-13 October 2006
Temperature effect: SiC vs. Si
10 -8
10 -9
10 -10
10 -11
10 -7 1000
67 °C
Current density [ A/cm 2 ]
Silicon
47 °C
27 °C
200
4H-SiC
67 °C
47 °C
27 °C
10 -12
1 10 100
Mean Electric Field [ kV/cm ]
Higher performance of SiC with respect to Silicon is significant above
room temperature, especially for relatively large area detectors in which the
leakage current constitutes the main noise source*.
*G. Bertuccio et al.,” A new generation of X-ray
detectors based on silicon carbide”, NIM A 518 (2004)
433–435
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RESMDD06, Florence, 10-13 October 2006
Experimental Results on SiC Detectors*
• 4 x 4 matrix
*G. Bertuccio, “Prospect for energy resolving X-
ray imaging with compound semiconductor pixel
detectors, NIMA 546 (2005) 232-241
• Pixel size: 400 μm x 400 μm
Sub-electron noise at RT!!!
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RESMDD06, Florence, 10-13 October 2006
SiC pixel detector: from 27 °C to 100°C
T = 100°C
797 eV FWHM
13.9 keV
17.8 keV
241 Am
*G. Bertuccio,
NIMA 546
(2005) 232-241
Counts
T = 27°C
315 eV FWHM
26.3 keV
Np L X-rays
0 5 10 15 20 25 30
Photon Energy [ keV ]
At high T the resolution is limited by the
Front-end, NOT by the detector!!!
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RESMDD06, Florence, 10-13 October 2006
Front-end noise
Necessity of a new
front-end with noise
of few electrons
New CMOS integrated charge
preamplifier with ENC=3.9 e - + 6.2 e - /pF
for detectors with 0.5 pF capacitance and
for power consumption of 2.3 mW*.
* courtesy of G. Bertuccio and S. Caccia, ”Progress in ultra low
noise ASIC’s for radiation detectors” to be published on NIM
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RESMDD06, Florence, 10-13 October 2006
Conclusions α and β
• Current
– Currents @ 500 V are very low even after fluences of the order of
10 16 n/cm 2 .
– Currents decrease after annealing at 80°C, 200°C and 400°C.
• Capacitance
– Capacitance is constant. The material turns to intrinsic
• CC
– CCE is 100% before irradation. CC is good until fluences of the
order of some 10 14 n/cm 2 . Before annealing , for fluences of the
order of 10 15 -10 16 n/cm 2 the CC for α and β is very low.
– After annealing at 80°C a slight increase of the collected charge is
observed, in the range of the experimental error. No recovery of the
damage!
– After annealing at 400°C for 30 min an increase of the CC of the
order of 40% is obtained.
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RESMDD06, Florence, 10-13 October 2006
Conclusion UV detectors
• 4H-SiC visible blind UV avalanche detectors with V BD =96 V
and R max =106 A/W at 270nm. At 370 nm R is equal to noise
limit
• EUV detectors: QE (0 V) > 50% from 230 to 295 nm, QE=
65% at 275 nm, (internal QE ≈100%). The rejection ratio of UV
to visible light is higher than 1000. QE (EUV) > 100% for λ<
50 nm, QE (EUV) > 30 e/photon at 3 nm.
• SPAPD detectors:V br ≈ 78 V. The peak QE ≈ 20% for λ= 270 -
280 nm. At 370 nm QE is equal to noise limit. Photon count rate
is about 4.5 MHz (89 signal pulses in 20 μs), n p of photons
absorbed per μs by the SPAD is 6. The average photon counting
efficiency is therefore 1.2%. At the peak λ = 353 nm, the photon
counting efficiency is estimated to be 2.6%.
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RESMDD06, Florence, 10-13 October 2006
Conclusion X-ray
• SiC has the same absorption length as Si
• SiC can give superior resolution at certain T and Areas
• Pixel and pad detectors have been fabricated
• SiC pixel detector: 315 eV FWHM @ 27 ° C
797 eV FWHM @ 100 °C
(due to Front-end)
• SiC pixel : sub-electron noise at RT
• New front-end with ENC=3.9 e - + 6.2 e - /pF
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RESMDD06, Florence, 10-13 October 2006
Acknowledgements
• Prof. A. Scorzoni, University of Perugia, Italy
• Dott. R. Nipoti, IMM-CNR of Bologna , Italy
• Dott. A Poggi, IMM-CNR of Bologna , Italy
• Ing. P. Maccagnani, IMM-CNR of Bologna , Italy
• Dott. S. Sciortino, Dipartimento di Energetica and INFN of Florence , Italy.
• Dott. S. Lagomarsino, Dipartimento di Energetica and INFN of Florence , Italy.
• Prof. Mara Bruzzi, Dipartimento di Energetica and INFN of Florence , Italy.
• Prof. G. Bertuccio, Politecnico of Milano , Italy
• IKZ institute of Berlin (Germany) for the epilayer growth,
• The clean room staff of “CNR-IMM Sezione di Bologna , Italy” for the device
realization
• The Jozef Stefan Institute (Ljubljana, Slovenia) for the neutron irradiation.
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RESMDD06, Florence, 10-13 October 2006
Appendix
AXUV
Photodiodes ,
International
Radiation
Detectors Inc.
39