vertex 2001 brunnen, switzerland phil allport gianluigi casse ashley greenall salva marti i garcia...

Vertex 2001 Brunnen, Switzerland

Phil AllportGianluigi Casse

Ashley GreenallSalva Marti i Garcia

Charge Collection Efficiency Studies with Irradiated Silicon

Detectors

Evaluation of trapping effects

The influence of ballistic deficit

Fits to the Charge Collection Efficiency

Discussion and Conclusions


Evaluation of Trapping Effects

Radiation damage to silicon detectorsincreases reverse currents, creates interface trapped charge, introduces traps reducing charge collection efficiencieschanges the effective doping concentrations

Studies of the latter effect have shown significant improvements under charged hadron irradiation when high concentrations of interstitial oxygen are introduced

However, unlike in the case of n-side read-out detectors, the charge collection efficiencies for p-side read-out detectors do not plateau with voltage until well above the depletion voltage

This is usually assigned to the effect of trapping


Old ATLAS Irradiated n-in-n Results

21014p/cm2


Detectors Studied

Studies carried out with SCT miniature (cmcm) p-side read-out micro-strip detectors (processed as test structures on ATLAS prototype wafers) using wide bandwidth (Phillips 6954) current amplifier

Comparisons with the large area devices using SCT-128 analogue read-out have demonstrated good agreement (G. Casse et al.)



Capacitance – Voltage Derived Depletion Voltage

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

0.0014

0.0016

0 50 100 150 200 250 300 350

Bias [V]

1/C

2 [p

F-2

]

1.90.11014p/cm2

Oxygenated MiniatureMicro-strip Detector

VFD = 100 7 V from fitting C(V)



Corresponding Charge Collection Efficiency vs Voltage

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0 200 400 600 800

Bias [V]

No

rma

lis

ed

co

lle

cte

d c

ha

rge

Q (10 ns)

Q (25 ns)

Q (40 ns)

Q (80 ns)

100 V



The effects of trapping can be parameterized in terms of effective trapping time (Kramberger et al.) or, equivalently, velocity dependent attenuation length (Marti i Garcia et al.)

In both cases, trapping is highest where the field is lowest

These parameterizations assume timescales such that the total untrapped charge is collected, integrating over transient effects.

No influence of ballistic deficit is included

Both analyses give values of (averaged over e and h) that agree. e,h eq = 1/eff e,h (trapping flux)


Influence of Ballistic Deficit

Since at the LHC electronics response times are close to charge collection times, signal loss due to incomplete charge integration must also be considered, which will also depend on the field within the detector.

Non-irradiated p-strip Detector



Oxygenated and non-oxygenated detectors have been studied which were irradiated in the CERN-PS and annealed to the minimum of the Neff vs time annealing curve



Detector label Fluence [p cm-2]Oxygenation[~2·1017 at. Cm-3]

NI Non-irradiated NoSO1 1.90.1 ·1014 YesSN1 1.90.1 ·1014 NoSO2 2.90.2 ·1014 YesSN2 2.90.2 ·1014 NoSO3 5.10.4 ·1014 YesSN3 5.10.4 ·1014 No

Several miniature detectors have been studied after irradiation and annealing.



0.00

0.20

0.40

0.60

0.80

1.00

1.20

0 200 400 600 800

Bias [V]

No

rmal

ise

d c

olle

cte

d c

har

ge

Q (10 ns)

Q (25 ns)

Q (40 ns)

Q (80 ns)

Miniature detectors irradiated to 1.91014p/cm2

Non-Oxygenated Oxygenated

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0 100 200 300 400 500 600 700 800

Bias [V]

No

rmal

ise

d c

olle

cte

d c

har

ge

Q (10 ns)

Q (25 ns)

Q (40 ns)

Q (80 ns)





0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 200 400 600 800

Bias [V]

Nor

mal

ised

col

lect

ed c

harg

e

Q (10 ns)

Q (25 ns)

Q (40 ns)

Q (80 ns)

0

0.2

0.4

0.6

0.8

1

1.2

0 200 400 600 800

Bias [V]

Nor

mal

ised

col

lect

ed c

harg

e

Q (10 ns)

Q (25 ns)

Q (40 ns)

Q (80 ns)





0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 200 400 600 800 1000

Bias [V]

No

rma

lise

d c

oll

ect

ed

ch

arg

e

Q (10 ns)

Q (25 ns)

Q (40 ns)

Q (80 ns)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 200 400 600 800

Bias [V]

No

rmal

ise

d c

olle

cte

d c

har

ge

Q (10 ns)

Q (25 ns)

Q (40 ns)

Q (80 ns)


Non-Oxygenated Detectors: Relative Ballistic Deficit

Oxygenated

0

0.2

0.4

0.6

0.8

1

1.2

0 100 200 300 400 500 600

Bias [V]

QV/Q

V(8

0 n

s)

Q (10 ns)

Q (25 ns)

Q (40 ns)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 200 400 600 800

Bias [V]

QV/Q

V(8

0 n

s)

Q (10 ns)

Q (25 ns)

Q (40 ns)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 200 400 600 800

Bias [V]

QV/Q

V(8

0 n

s)

Q (10 ns)

Q (25 ns)

Q (40 ns)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 200 400 600 800 1000

Bias [V]

QV/Q

V(8

0 n

s)Q (10 ns)

Q (25 ns)

Q (40 ns)

5.11014 p/cm22.91014 p/cm2

1.91014 p/cm2Non-irradiated


Oxygenated Detectors: Relative Ballistic Deficit

5.11014 p/cm2

2.91014 p/cm21.91014 p/cm2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 200 400 600 800

Bias [V]

QV/Q

V(8

0 n

s)

Q (10 ns)

Q (25 ns)

Q (40 ns)

0

0.2

0.4

0.6

0.8

1

1.2

0 200 400 600 800

Bias [V]

QV/Q

V(8

0 n

s)

Q (10 ns)

Q (25 ns)

Q (40 ns)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 200 400 600 800

Bias [V]

QV/Q

V(8

0 n

s)

Q (10 ns)

Q (25 ns)

Q (40 ns)



The above results suggest that, particularly at high doses, the ballistic deficit is not a major factorfor LHC speed operation

In the following fits, sufficient integration time has anyway been allowed such that the only charge loss is due to trapping

Free parameters: attenuation length ,depletion voltage VFD total generated charge Q0

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 200 400 600 800 1000

Bias [V]

Q/Q

0

Oxygenated

Non-oxygenated

1.91014 p/cm2



2.91014 p/cm2

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 200 400 600 800 1000

Bias [V]

Q/Q

0

Oxygenated

Non-oxygenated

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 200 400 600 800 1000Bias [V]

Q/Q

0 Oxygenated

Non-oxygenated

5.11014 p/cm2



Detector label

Fluence[p cm-2]

Oxygenenrichme

nt

VFD [V](From C-V)

VFD [V](From CCE)

[m]

NI Non irr. No 49 2 50 2

SO1 1.90.1 · 1014 Yes 100 7 90 2 1338 15

SN1 1.90.1 · 1014 No 150 8 137 2 1407

220

SO2 2.90.2 · 1014 Yes 121 7 130 2 1224

138

SN2 2.90.2 · 1014 No 218 15 214 4 1313

122

SO3 5.1 0.4 · 1014 Yes 181 15 196 3 731 84

SN3 5.10.4 · 1014 No 320 20 348 7 781 55



The fitted values of VFD agree with each other and with oxygenated data from RD48 (CERN LHCC 2000-009) taking account of the proton damage factor

The fitted values of Q0:18.10.3, 18.20.3, 17.70.3, 18.10.6, 18.20.4 and 18.30.4 are all consistent and agree with the pre-irradiation value 17.90.3



The dependence of Q/Q0 and therefore on leads to a value of eff = 5.60.610-16cm2/nsAssuming this value allows extrapolation of CCE to high

0

0.2

0.4

0.6

0.8

1

1.2

0 1E+14 2E+14 3E+14 4E+14 5E+14 6E+14

Fluence [p cm-2]

Q/Q

0

(Charge collected at VFD)/Q0 - Ox. detectors

(Maximum collected charge)/Q0 - Ox. detectors

(Charge collected at VFD)/Q0 - Non-ox. detectors

(Maximum collected charge)/Q0 - Non-ox. detectors



Because for p-strip read-out, the trapping significantly affects the CCE(V), the improvements in VFD due to oxygenation do not give correspondingly large effects in terms of CCE The trapping dependence on the field leads to CCE(VFD) being higher for non-oxygenated than oxygenated detectors by ~5%

Read-out from the high-field n-side gives less dependence on trapping leading to the CCE(V) V behaviour below VFD

This would imply that for high doses, n-side readout should benefit more from oxygenation of the substrate



The LHC-b vertex detector is proposed to use oxygenated n-strip detectors for which the first prototypes have just been delivered to Liverpool and are currently being irradiated in the CERN PS



LHC-b uses back-to-back thinned disks for r and plus double-metal routing



LHC-b and the pixel systems of ATLAS and CMS need to maximise their survival; n-side readout oxygenated detectors look to offer the best possibilities

Super-LHC with factor of 10 increased luminosity could also need such technology



Detectors produced with n-side read-out do suffer from the disadvantage of requiring potentially expensive double-sided processing

Use of p-type substrates does provide a viable alternative where cost is of paramount importance

Comparison of p-type and n-type detectors after 31014 p/cm2

vertex 2001 brunnen, switzerland phil allport gianluigi casse ashley greenall salva marti i garcia...

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