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Paradoxes Paradoxes of steadyof steady--state and pulse operational modestate and pulse operational mode

characteristics of silicon detectorscharacteristics of silicon detectorsirradiated by ultrairradiated by ultra--high doses of high doses of γγ--raysrays

E. Verbitskaya1, Z. Li2, E. Fretwurst3, V. Eremin1, I Ilyashenko1, J. Kierstead2, C. Wilburn4, R. Röder5

1Ioffe Physico-Technical Institute of Russian Academy of Sciences, Russia2Brookhaven National Laboratory, USA

3Institute for Experimental Physics, Hamburg University, Germany4Micron Semiconductor, UK

5CiS Institute for Microsensors, Germany

1st RD50 Workshop on radiation-hard semiconductor devicesfor very high luminosity colliders

CERN, 2-4 October 2002

E. Verbitskaya et al, 1st RD50 Workshop, CERN, 2-4 October 2002

OutlineOutline1. Motivation and earlier results2. Experimental

Steady-state characteristics3. Dependences of Vfd and Neff vs. dose in detectors from standard

and oxygen-rich Si:• experimental C-V dependencies;• space charge sign verification using TCT• modeling of Neff vs. D dependencies4. Changes of I-V characteristics with dose accumulation5. Temperature dependencies of the reverse current

Characteristics of pulse operational mode6. Distortions of current pulse response shapes in detectors from standard

and oxygen-rich Si irradiated by ultra-high dose of γ-rays7. Room temperature polarization in detectors from oxygenated Si

8. DiscussionConclusions

Motivation and earlier resultsMotivation and earlier resultsHigh doses of γ- rays play a significant role in a linear collider

0

50

100

150

200

250

300

0 100 200 300 400

Dose (Mrad)

Vfd

(V) n

orm

alis

ed to

300

µm

1.1 kOhm cm, Oxygenated1.1 kOhm cm, Standard1.2-3 kOhm cm,Oxygenated1.2-3 kOhm cm, Standard

B. Dezillie et al, IEEE Trans. NS-47(2002) 1892

Standard Si: gradual Vfd reduction till the SCSI

Si oxygen-rich (Si HTLTprocessed at BNL):

no SCSI up to 575 Mrad


ExperimentalExperimental

BNL detectors: n-Si Wacker; ρ = 1 kOhm⋅cm; orientation <111>; Oxygenation: BNL High Temperature Long Time process

+ Thermal Donors: Si HTLT(TD)CIS detectors: n-Si Wacker; ρ = 4 kOhm⋅cm; orientation <111> and <100>;

Oxygenation: CIS Diffusion Oxygen Float Zone (DOFZ) process;oxygenation time: 24, 48, 72 h

MS detectors: n-Si Wacker; ρ = 15 kOhm⋅cm; orientation <111>;Oxygenation: MS DOFZ process + TD

Experimental technique1. C-V and I-V measurements;2. TCT measurements with a red laser (λ = 660 nm); 3. I-T measurements

Irradiation: BNL, 60Co source


Detectors irradiated up to ultraDetectors irradiated up to ultra--high Dhigh D


producer # material orientation D (Mrad)

904-96 standard 339904-100 -“- 1647906-97 oxygenated + TDs 947

BNL

906-101 -“-

<111>

9471940-18-5 standard 3391940-18-6 -“- 8352015-11-5 oxygenated + TDs 1758

MS

2015-11-6 -“-

<111>

947CA0749 standard 1647CB0249 oxygenated 1758CC1549 -“- 947

CIS

CD2040 -“-

<111>

1758CE1549 standard 1260CF0449 oxygenated 947CG1049 -“- 947

CIS

CH2149 -“-

<100>

1758

SteadySteady--state characteristics of state characteristics of γγ--irradiated detectorsirradiated detectorsCC-- V characteristicsV characteristics

SiSi standard, standard, Ultra-high dose: D = 0-1.65 Grad CIS <111> CA0749

1 10 100

10

100

C (

pF)

V (Volt)

D (Mrad): 42.7 190 338 519 835 1050 1260 1647

Standard Si:• Vfd changes

non-monotonically (similar to n/p)

• “bump” in C-V characteristicsmay appear after Vfd minimumwas reached


f = 10 kHz


SCSI in detectors from standard SCSI in detectors from standard SiSi

D = 338 Mrad BNL 904-100

650 660 670 680 690 700

-3

-2

-1

0

1

2

3

4

Sig

nal (

arb.

uni

ts)

Time (ns)

V (Volt): 20 35 45 50 55 60 70 80 90 100 120 150

SCSISCSI is observed in all detectorsfrom standard Si

Di is different

Laser illuminationon the p+ side:electron collection


CC--V characteristics: V characteristics: SiSi oxygenatedoxygenated

Ultra-high dose: D = 0-1.76 Grad MS # 2015-11-5

1 10 100

10

f = 10 kHz

C (

pF)

V (Volt)

D (Mrad): 42.7 96.2 190 947 1160 1370 1758

Si oxygenated:Vfd increases slowly and monotonicallywith D


SiSi oxygenated: positive space charge detectorsoxygenated: positive space charge detectors

Ultra-high dose D = 1.76 Grad CIS <111> CB0249

400 420 440 460

-2

0

2

4

Sig

nal (

arb.

uni

ts)

Time (ns)

V (Volt): 110 120 130 140 150 170 200 230 250 300

hole collectionhole collection(laser illumination on the n+ side)

Space charge is positivepositive!

Full depletion voltage in detectors from standardFull depletion voltage in detectors from standard SiSi


0 200 400 600 800 1000 1200 1400 1600 18000

100

200

300

400

500

D (Mrad)

Vfd

Vfd (

Vol

t) 904-100 1940-18-6 CA0749 CE1549

Vfd as-measured:difference in thickness~5.5%


Standard Standard SiSi: : QQ--V dependenciesV dependencies

0 100 200 300 400 500 600 700

1

Vp-off

= 487 V

VQsat

= 595 V

Q (

arb.

uni

ts)

V (Volt)

D, Mrad: 338.7 392.2 461.2 510 620.4 719.8 835 1050 1259 1647

Vp-off – pinch-off occurs

VQsat – E(x) is linear, Q-V dependence is close to saturation

Vp-off

p+ n+

V2

V1

pinch

-off

VQsat>Vfd

Standard Standard SiSi: : comparison of Ccomparison of C--V and QV and Q--V data on V data on VVfdfd


0 200 400 600 800 1000 1200 1400 1600 18000

100

200

300

400

500

600

16%

V

fd (V

olt)

D (Mrad)

Vfd (C-V)

Vp-off

(Q-V) V

Qsat (Q-V)

BNL 904-100

• Vfd derived from C-V is close to Vp-off

• Vfd derived from Q-Vdependencies (VQsat)

corresponds to Vat which E is closeto linear and >Vfd(C-V)

Results are similar to earlier data in detectors irradiated by p/n

[V. Eremin et al, 6th ROSE Workshop on Rad. Hard. Silicon Det., CERN/LEB 2006-006, Oct 2000, pp. 387-390]

The difference betweenVfd (C-V) and VQsat

increases with dose


Space charge concentration NSpace charge concentration Neffeff in detectors from standard in detectors from standard SiSi

0 200 400 600 800 1000 1200 1400 1600 1800

-8

-6

-4

-2

0

2

4

Nef

f (10

12 c

m-3)

D (Mrad)

experiment: BNL <111> 904-100 MS <111> 1940-18-6 CIS <111> CA0749 CIS <100> CE1549

fit: lines

Neff = Nd0⋅exp(-γD) -βD

# orientation Nd0 (cm-3) γ (Mrd-1) β (cm-3Mrd-1) Di (Mrd)904-100 <111> 3.86⋅1012 2.47⋅10-3 4.8⋅109 325

1940-18-6 <111> 7.23⋅1011 (7.0⋅10-5)? 8.1⋅109 88CA0749 <111> 8.91⋅1011 1.88⋅10-3 2. 7⋅109 190CE1549 <100> 9.36⋅1011 7.2⋅10-4 4.5⋅109 190

γ - donor removal rateβ - acceptor introduction rate


VVfdfd and Nand Neffeff in detectors from standard and oxygenated in detectors from standard and oxygenated SiSi

0 200 400 600 800 1000 1200 1400 1600 1800

-6

-4

-2

0

2

Neff

Nef

f (10

12 c

m-3)

D (Mrad)

0 200 400 600 800 1000 1200 1400 1600 18000

100

200

300

400

500

Vfd

Vfd (

Vol

t)

Si stand., 1940-18-6 Si oxyg., 2015-11-6 -"- 2015-11-5

In contrast to standard Siin oxygenated detectorsVfd increases slowlyand monotonically with dose

Positive space chargeis accumulated with Dup to ultra-high dose of 1.75 Grad

Donor type defect introductionin oxygenated Si is uniquefor γ-irradiation


Modeling NModeling Neffeff vs. D dependencies in detectors from oxygenatedvs. D dependencies in detectors from oxygenated SiSi

0 200 400 600 800 1000 1200 1400 1600 1800 20000.0

0.5

1.0

1.5

2.0

2.5

Nef

f (10

12 c

m-3)

D (Mrad)

experiment: CIS CB0249 CIS CD2049 CIS CH2149 MS 2015-11-5

fit: CB0249 (0-1.76 Grd) -"- (0-1.37 Grd) CD2049 CH2149 2015-11-5

# oxygen.time (h)

dose rangeGrad

Nd0cm-3

Nd1cm-3/Mrd

m

2015-11-5 <111> ? 0-1.76 1.625⋅1012 1.48⋅107 1.449CB0249 <111> 24 0-1.76 1.13⋅1012 5.24⋅104 2.27CB0249 <111> 24 0-1.37 1.09⋅1012 1.52⋅107 1.47CD2049 <111> 72 0-1.76 1.038⋅1012 2.54⋅108 1.125CH2149 <100> 72 0-1.76 7.89⋅1011 7.89⋅107 1.266

Model: Nd0 + Nd1⋅Dm -

• donor type defect introduction• superlinear dependence on D

The power in superlinear dependence decreases withoxygenation time?


II--V V characteristicscharacteristics

1 10 100

10-3

10-2

10-1

100

101

pinch-off

SCSI

I (µA

)

V (Volt)

D (Mrad): 0 42.7 190 284 392.2 720 1260 1647

1 10 100

10-2

10-1

100

I (µA

)

V (Volt)

D (Mrad): 42.7 96.2 190 392.2 947 1160 1370 1760

SiSi oxygenatedoxygenated, MS 2015, MS 2015--1111--55Si standard, BNL 904-100

• Current values are different at the same D• Standard Si, beyond SCSI: at V<Vfd edge current on the n+-side,different from stabilization of the reverse current in detectorsas-irradiated by high F of neutrons/protons


Reverse current density on dose dependenciesReverse current density on dose dependencies

0 200 400 600 800 1000 1200 1400 1600 18000.0

0.5

1.0

1.5

2.0

2.5

I fd (µ

A)

D (Mrad)

Si stand., CA0749 Si oxygenated

CB0249 CC1549 CD2049

Comparison of standard and oxygenatedComparison of standard and oxygenated SiSi

0 200 400 600 800 1000 1200 1400 1600 18000.0

0.5

1.0

1.5

2.0

sublinearlinear:

(1-1.5)x10 -15 A/cm2rd

jfd(D)

j fd (µ

A/c

m2 )

D (Mrad)

MS 2015-11-5 CB0249 <111> CD2049 <111> CH2149 <100> linear fit:

2015-11-5

Oxygenated Oxygenated SiSi

Standard Si:reverse current density at Vfd shows

superlinear increase with dose

Oxygenated Si:D < 1 Grad: linear increasedamage coefficient of 10-15A/cm2⋅radD > 1 Grad: sublinear increase

j at Vfd

stand.

oxygen.


Reverse current vs. temperature dependencesReverse current vs. temperature dependences

0.0035 0.0040 0.0045 0.0050

10-4

10-3

10-2

10-1

100

101

stand.

oxygen

j (µA

/cm

2 )

T-1 (K-1)

Micron Semicond. Si stand., 1940-18-6; 835 Mrd Si oxyg., 2015-11-6; 947 Mrd

CIS <111>: Si stand., CA0749; 16470 Mrd Si oxyg., CC1549; 957 Mrd Si oxyg., CB0249; 1759 Mrd

D: 0.84-1.76 GradT: 295 to 200 KBulk generation currentis analyzed: I at V >I at V > VVfdfd

Model: Shockley-Read-Hall statistics

I-T analysis: [E. Verbitskaya et al., 5th ROSE Workshop, March 2000, CERN LEB 2000-005, p.300]

Si standard: various slope at different TEffective generation level: Ej = 0.64-0.68 eVtwo gen. levels: midgap level ~0.57 eV (lower T); and Ej ≈ 0.8 eV

Si oxygenated: single slope, Ej = 0.77-0.79 eV

Detector characteristics in pulse operational modeDetector characteristics in pulse operational mode


400 410 420 4300

5

10

15

20D = 519 Mrad

laser illuminationof the p+ side

Sig

nal (

arb.

uni

ts)

Time (ns)

V (Volt): 110 115 120 125 130 135 140 145 150 160 170 180 200 220

400 420 440 460

-2

0

2

4

Sig

nal (

arb.

uni

ts)

Time (ns)

V (Volt): 110 120 130 140 150 170 200 230 250 300

Si oxygenated CB0249

electron collectionelectron collection

hole collectionhole collection

D = 1.76 Grad

Si standard BNL 904-100

DJ effect –– non-uniform double peak E(x)in heavily irradiated detectors originated from free carrier trapping from detector reverse current [V. Eremin et al, NIM A476 (2002) 556-564]

• no initial fast rise of response• abnormal increase of the slope

• time dependent Neff (+Neff ↑)• E at the n+ contact drops to zero


Room temperature polarization in detectors from oxygenated Room temperature polarization in detectors from oxygenated SiSi

• Initially: collection in fully depleted detector, E > 0• Holes are trapped during drift and increase positive Neff

• difference between Emin and Emax increases in time• pulse response degradation occurs due to polarization

640 650 660 670 680 690

0

5

10

15

in darkness

laser illuminationof n+ side

15 min

12 min

sign

al (

arb.

uni

ts)

t (ns)

D = 1.76 Grad; V = 300 V (V ≈ 2 Vfd)

hole collection: degradation of pulse response

0 200 400 600 800 1000 12000.0

0.2

0.4

0.6

0.8

1.0

Q n

orm

aliz

ed

t (s)

V (Volt): 150 200 300

0 200 400 600 800 1000 12000.0

0.2

0.4

0.6

0.8

1.0

Q n

orm

aliz

ed

t (s)

Dependence of CCE degradation on reverse bias voltageDependence of CCE degradation on reverse bias voltage

CCEh degradation is sharp• E (at the n+ contact) drops to 0,• neutral base region evolves at n+

• holes can’t be collected• the higher is V, the larger is top

hole collection

CCEe degradation is gradual• CCE ~ w/d,• initially: w = d,• at t>top gradual reduction of w

electron collection


at V fixed top is thesame

for e and h

640 650 660 670 680 690

0

5

10

15

0 100 200 300 400 500 6000.0

0.2

0.4

0.6

0.8

1.0

electron drift:

laser illuminationof p+ side

Q n

orm

aliz

ed

t (s)

laser switched on in all measurem

laser switched off between the measurem.

colored lines: bias on, laser onblack lines: bias on, laser off30 s between measurements

sign

al (

arb.

uni

ts)

t (ns)


Polarization controlled by trapping of thermally generated holesPolarization controlled by trapping of thermally generated holes

detector is permanently biased;• laser is switched on and off -

no difference in top, no influencefrom laser generated e/h

Holes are trapped from detector reverse current

Polarization: observed earlier in Sidetectors irrad. by neutrons and operated at cryogenic T[B. Dezillie et al, NIM A452 (2000) 440]

Paradox for γ-irradiated detectors:• polarization is observed at RT;

• hole trapping in SCR with +Neff

Possible reason for RT polarization:new defects in oxygenated Si induced by γ-rays:Ej = 0.8 eV, larger τdetr

Electron collection


DiscussionDiscussion 1.1. Paradoxes of Paradoxes of γγ--irradiatedirradiated SiSi detectorsdetectors

• Defects responsible for radiation damage and different introduction rate?• Oxy-Si: DD or SD? ∆Neff = (0.8-1.1) ⋅1012 cm-3; NSD = 3⋅1011 cm-3 (low T data)

Si standard Si oxygenated

PPaarraaddooxx: positivesuperlinear: Nd0 + Nd1⋅D

m

m = 1.1-1.5Neff

Neff = Nd0⋅exp(-γD) -βD

negative after SCSI

linear: β ~ 109 cm-3Mrd-1 D > 0.6 Grd:linear

β+ ~ 108 cm-3Mrd-1

sublinearI (Vfd):

PPaarraaddooxxsuperlinear D < 0.7 Grd:

linear:α ~ 10-9

A/cm2⋅MrdPulse

operationmode

D > 0.5 Grd:

distortions due to DJ effect

PPaarraaddooxx:- RT polarization at D ≥ 1 Grd;

- hole trapping in SCR with +Neff

DiscussionDiscussion


2. Radiation hardness improvement in oxygenatedRadiation hardness improvement in oxygenatedSiSi detectorsdetectors

Vfd0 – full depletion voltage before irradiation;VfdF – full depletion at the range border (D = 0.95 or 1.65 Grad)jF – reverse current density at VfdF;R = VfdF/Vfd0 – Vfd increase ratio within the dose range;GGFF == RRstst//RRoxyoxy - gain in thegain in the VVfdfd reductionreduction in oxygenated detectors with respect to detectors from standard Si irradiated to the same border dose

* Vfd0 is smaller for CIS <100>

The difference in GFand current ratio betweenthe dose ranges arises from different dependenciesof Vfd and j on D

# range,Grad

GF jF st/ jF oxy

MS 0-0.84 22.5 4.4CIS

<111>0-0.950-1.75

2.0* 2.7

3.64.6

CIS<100>

0-0.950-1.75

3* 4

3.23.3


ConclusionsConclusions

1. The radiation hardness improvement of detectors from oxygenated Si irradiated by γ-rays actually extends now up toultra-high dose range of 1.75 Grad

2. The gain in the Vfd reduction in oxygen rich detectors with respect to detectors from standard Si is ~2 in the range of 1 Grad and increases to ~3 in the ultra-high dose range 1-1.75 Grad

3. ParadoxParadox of oxygenated Si: • inhibited degradation of steady-state characteristics even at ultra-high dose;• collapse at D ~ 1 Grad due to RT polarization in pulse operational mode!

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