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The Sixth International “Hiroshima” Symposium on the Development and Application of Semiconductor Tracking Detectors. Cryogenic Si detectors for Ultra Radiation Hardness in SLHC Environment Zheng Li (BNL) On behalf of CERN RD39 Collaboration. - PowerPoint PPT Presentation
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Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006
The Sixth International “Hiroshima” Symposium on the Development and
Application of Semiconductor Tracking Detectors
Cryogenic Si detectors for Ultra
Radiation Hardness in SLHC Environment
Zheng Li (BNL)
On behalf of CERN RD39 Collaboration
Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006
CERN RD39 Collaboration: Cryogenic Tracking Detectors
Outline
o Trapping effect on Charge Collection Efficiency (CCE) in SLHC
LHe temperature TCT setup
Operation of current-injected-detectors (CID)
CCE measurements on CID
Summary
Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006
Trapping effect on CCE in S-LHC
CCEGF is a geometrical factor
fdeff V
V
d
w
eN
Vw and
2 0
CCEt is related with trapping
For fluence less than 1015 n/cm2, the trapping term CCEt is insignificantFor fluence 1016 n/cm2, the trapping term CCEt is a limiting factor of detector operation !
Depletion term
Trapping term
CERN RD39 Collaboration: Cryogenic Tracking Detectors
tdrttGF e
d
wCCECCECCE /
Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006
CEE Vs. V/Vfd & Trapping
CCE=Zta*(1-Eta)
0.00
0.100.20
0.300.40
0.500.60
0.700.80
0.90
Z-ta (V/Vfd)
0.000.10
0.200.30
0.400.50
0.600.70
0.800.90
1.00 E-ta (Tr
apping)
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
CC
E
c/modeling-98/cce-VfdV-trapping.tc
ImproveNeff Reduce
trapping
Combined effect (RD39)
To get better CCE:
>1015 n/cm2
)
1(
/ tdrt
e
1/2
Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006
TRAPPING
tth Nvt 1
The thermal velocity vth 107cm/s
1016cm-2 irradiation produces NT3-5*1016 cm-3 with 10-14cm2
Even in highest E-field (Saturation velocity, 107 cm/s), carrier drifts only 20-30 m before it gets trapped regardless whether the detector is fully depleted or not !
In S-LHC conditions, about 90% of the volume of d=300m detector is dead space !
CERN RD39 Collaboration: Cryogenic Tracking Detectors
On average (e and h) it gives a t 0.2 ns!
Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006
• Trapping time: t
• 1/ t = n
• e = 7.5010-7 cm2/s
• h = 3.75 10-7 cm2/s
• for 1016 neq/cm2:
te = 0.13 ns
th = 0.26 ns
t = 0.20 ns as average
Trapping distance (or effective charge collection distance) is:
deff ≤ t Vs = 20 μm << d, the detector thickness or depletion depth
The main limiting factor is trapping for SLHC!
CERN RD39 Collaboration: Cryogenic Tracking Detectors
H.W. Kraner et al., Nuclear Instruments and Methods in Physics Research A326 (1993) 350-356
Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006
SiO2
Al
Effective CCE thickness d : thickness (200- 300 μm)
w: depletion depth ( ≤ d)
t: trapping distance (20-50 µm)
d
W substrate
p-type
AlAlAl
p+
n+ n+ n+
t
Thickness d
Q(t) = Q(w) t/w
Q(w) = W/d Q0
Q(t) = Q0 t/d
Thickness t (fully depleted, t = w)
Q(t) = Q(w) t/w = Q(w)
Q(w) = w/d Q0 = t/d Q0
Q(t) = Q0 t/dThe same!
Effective thickness = t
e
Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006
Solution CCE improvement due to Technology/
implementation difficulties
Replacement every 1-2 years New detectors Hard to access the inner region
3D Si detectors Small Vfd
Small drift distance t
Complicated processing technology
Column spacing t should be < 40 m
Possible surface damage problem to ionizing radiation
Cryogenic Si detectors Fixed electric field (small bias)
Freezing traps (low trapping)
Low leakage current
Difficult to implement cryogenic system
Elevated temp annealing
(DRIVE)
(MCZ Si only, 400 ºC)
Annealing out of defect levels related to:
Leakage current, space charges
And trapping
Difficult to implement annealing in a full detector system
Possible Si detector solutions for SLHC’s most inner region
Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006
DETRAPPING
The detrapping time-constant depends exponentially on T
kTECth
td eNv /
1
If a trap is filled (electrically non-
active) the detrapping time-constant is crucial
For A-center (O-V at Ec-0.18 eV with 10-15 cm2 )
CERN RD39 Collaboration: Cryogenic Tracking Detectors
T(K) 300 150 100 77 60 55 50 48 47 46
d 3.7 ns 3.9 s 4 ms 2 s 1.22 hrs
1.2 days
53 days
302 days
2.1 years
5.47
years
Hole trap
Electron trap
T> 77K
Hole trap
T< 77K
filled
filled
Electron trap
EC
EV
EC
EV
Fill Freeze
Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006
• A fast TCT setup at CERN with sub-LN2 temp for CCE measuements
• All components of the setup have been made• The electical part (TCT with ps laser) and the He
cryostat are now operational• The final calibration and actual CCE measurements at
sub-LN2 temperatures are now underway
CERN RD39 Collaboration: Cryogenic Tracking Detectors
LHe Temp TCT Setup
First TCT signal of a Si detector He cryostat, to 40 K in 2 hours
He cryostat
Signal recording
Sample chamber
295 K
160 K
250 K
Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006
CERN RD39 Collaboration: Cryogenic Tracking Detectors
Current injected detector (principle of operation)
P+ P+
+Jp
Jp = epμE
divJ=0
divE=ptr
E(x=0) = 0 (SCLC: Space Charge Limited Current mode)
The key advantage: The shape of E(x) is not affected by fluence
x
d
x
d
VxE
2
3)(
d
VEm
2
3
E(x)
Em
V. Eremin, RD39, CERN, November 11, 2005
Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006
E(x) E(x)E(x)
x x x
“Diode” mode
p>ptr
E(x) ~ E(0) + ax
Deep Level saturation p >> ptr E(x) = ax
SCLC mode
Ndl>ptr
E(x) ~ SQR(x) J ~ V2
Evolution of E(x) in CID with the injected current
Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006
log J
log V
Ohmic, J ~ V
SCLC, J ~ V2
DL saturation
“Diode”
I-V characteristic of CID
Proof of CID concept: – observation of SCLC and DL saturation behavior
Problem: - optimal range of V for CID operation
Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006
CID I-V simulation
Sample parameters Physical constants Calculated valuesd [cm] 0.035 eps0[F/m] 8.85E-14 mu [cm2/V*s]
Uc[V] 0 eps 11.7 VsN0[cm-3] 0.00E+00 q[C] 1.60E-19 Vth*Nc 4.13E+26Operation parameters k[J/K] 1.38E-23 Vth*Nv 1.25E+26
Ub [V] 30 oe [cm 2̂/Vs] 2.08E+03 Nc[cm-3] 2.1741E+19Temperature 250 vse [cm/s] 1.12E+07 Nv[cm-3] 8.6963E+18
dX [cm] 1.00E-04 be[T] 7.82E-01 ni[T],cm-3 7.23E+07
injected current oh [cm 2̂/Vs] 8.17E+02
Egen, eV 0 vsh [cm/s] 8.14E+06 IntN(d) 0.00E+00
Sig(e), cm2 0.00E+00 bh[T] 9.87E-01 Vth(e),cm/s 1.90E+07
Sig(h), cm2 0.00E+00 Eg (eV0 1.12 Vth(h),cm/s 1.44E+07
M, cm-3 0.00E+00 Parameter Ef, eV 0.56Jn [A/cm2] 0.00E+00 Calculated Ef, eV 0.01 DL #
Jp [A/cm2] 1.00E+00 D/A, 0/1 0 1 0 1electrons holes electrons holes electrons holes electrons holes
Et=Edl-Ev 1.117 0.6 0.48 0.64 0.55 0.57
E(x) calculation sig/e[cm2] 1.00E-15 1.00E-17 1.00E-15 5.00E-15
Iterations 2 Imin, A/cm2 1.00E-12 sig/h[cm2] 1.00E-15 1.00E-15 1.00E-15 5.00E-15
Kdesipaiton 0.8 points 50 Ndl[cm-3] 0.00E+00 0.00E+00 2.80E+12 0.00E+00
Imax, A/cm2 1.00E+00 Sig*Vth 1.90E-08 1.44E-08 1.90E-10 1.44E-08 1.90E-08 1.44E-08 9.49E-08 7.19E-08
detrap.prob. 3.59E+11 3.97E-12 1.39E-01 1.03E-01 5.31E-02 2.69E+01 6.82E+00 5.23E+00
Row X E0(x) E1(x) n(x) p(x) Ff(x) Neff(x) Ff(x) Neff(x) Ff(x) Neff(x) Ff(x) Neff(x)
# cm V/cm v/cm cm-3 cm-3
I-V calculationMACRO
shallow donors deep acceptor deepdonor shallow acceptors
0.0E+0
5.0E+3
1.0E+4
1.5E+4
2.0E+4
2.5E+4
3.0E+4
0 0.01 0.02 0.03 0.04 0.05
E(x)
0.0E+005.0E+121.0E+131.5E+132.0E+132.5E+133.0E+13
0.00 0.02 0.04 0.06
Neff
1.E+001.E+021.E+041.E+061.E+081.E+101.E+121.E+14
0.00 0.02 0.04 0.06
n(x)p(x)
start
CID I-V simulation software
Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006
CERN RD39 Collaboration: Cryogenic Tracking Detectors
I-V characteristics of CID
A12, Cz(PTI), P+- N - N+, Fn=1015cm-2
1.E-10
1.E-09
1.E-08
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1 10 100 1000
Bias, V
Cu
rren
t, A
/cm
2
180k
200k
220k
250k
Fit 180K
Fit 200K
Fit 220K
Fit 250K
Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006
I-V characteristics of CID
1.E-10
1.E-09
1.E-08
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1 10 100 1000 10000
Voltage (V)
Cu
rre
nt
de
nc
ity
(A
/cm
2)
5e14 cm-2
1e15 cm-2
3e15 cm-2
Fit
Fit
Fit
Fit, 1e16 cm-2
CERN RD39 Collaboration: Cryogenic Tracking Detectors
220 K
Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006
SLHC fluencec
-65 C
Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006
CERN RD39 Collaboration: Cryogenic Tracking DetectorsMain advantages CID over standard PN detectors
1. The detectors are always fully depleted
2. The electric field profile does not change with fluence
3. Much lower bias voltage is needed
4. The higher the radiation fluence, the lower the operation current at given bias and temperature
5. The operation bias range increases with fluence
6. No breakdown problem due to self-adjusted electric field by space charge limited current feedback effect
7. Simple detector processing technology (single-sided planar technology)8. Injection can also be used to deactivate trapping centers --- CCE
Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006
CCE to 90Sr source at various temperatures for CID
CID Mode
Forward bias (250 V)
Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006
Φn = 11015 cm-2, T = 180 K, MIPs (1050 nm laser)
CID mode
Standard mode
Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006
0.00E+00
5.00E-13
1.00E-12
1.50E-12
2.00E-12
2.50E-12
0 50 100 150 200 250 300 350
Forward voltage [V]
Co
llect
ed C
har
ge
[arb
.]
0.0E+00
5.0E-03
1.0E-02
1.5E-02
2.0E-02
2.5E-02
3.0E-02
3.5E-02
4.0E-02
4.5E-02
0 1E-09 2E-09 3E-09 4E-09 5E-09 6E-09 7E-09 8E-09
Time [s]
TC
T s
ign
al [
arb
]
-300 V
-250V
-200V
-150V
Measurements from He cryostat, at 60K
CID mode
P-type MCZ, red laser1x1015/cm2
Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006
Charge Injected Diode
high p : continuous (DC) illumination of n+ side by red laser:
nn++
changing Neff (DC)
probing pulse (holes)
probing pulse (elec.)
0evS
Ip
h
Increase of leakage current due to illumination
drift time of holes through the detector
Neff controlled by:
•illumination intensity ( p )•operation voltage ( p )•temperature (trapping -detrapping process)
pp++
Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006
Charge Injected Diode
A significant reduction of VFD in case of continuous hole injection!
electron current pulseelectron current pulse hole current pulsehole current pulse
eqeq=5x10=5x101313 cm cm-3 -3 (after ~10 days at 20(after ~10 days at 20ooC)C)
Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006
CCE Measurements on CID CERN RD39 Collaboration: Cryogenic Tracking Detectors
DC injection with a red laser (electrons or holes)
Or current injection (forward bias)
OK for T<173K
OK for T<173K
OK for T<173KOK for T<173K
0.25 cm2
OK for T<173K
OK for T<173K
OK for T<173KOK for T<173K
0.25 cm2
0.25 cm2
SLHC fluencec
Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006
CCE to 90Sr source at various temperatures for CID
CCE to 90Sr source at various temperatures for CI D
Best for forward injection
0.25 cm2CCE to 90Sr source at various temperatures for CI D
Best for forward injection
0.25 cm2
0.25 cm2
Close to 0 at RT!
SLHC fluencec
Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006
CERN RD39 Collaboration: Cryogenic Tracking Detectors
Summary
o To increase CCE for SLHC, cryogenic operation of Si detectors at cryogenic temps may be necessary
Trapping can be frozen at such low temps
CID can stablize the detector electric field and increase the detector CCE
CCE measurements on CID at crogenic temperatures with laser and forward current injection have shown significant increase in CCE
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