Electric field distribution in irradiated MCZ Si detectors

1

Electric field distribution Electric field distribution in irradiated MCZ Si detectorsin irradiated MCZ Si detectors

E. Verbitskaya, V. Eremin, I. IlyashenkoIoffe Physico-Technical Institute of Russian Academy of Sciences

St. Petersburg, Russia

Z. LiBrookhaven National Laboratory, Upton, NY, USA

J. Härkönen Helsinki Institute of Physics, CERN/PH, Geneva, Switzerland

Marko Mikuž, Vladimir CindroJožef Stefan Institute, Ljubljana

Chris ParkesGlasgow University

9 RD50 Collaboration WorkshopCERN, Geneva, Oct 16-18, 2006

2

OutlineOutline

1. Background: E(x) distribution in heavily irradiated detectors

2. Approach for simulation of detector Double Peak response and E(x) profile reconstruction with a consideration of electric field

in the “neutral” base

3. Comparison of experimental results on DP pulse response of MCZ Si detectors irradiated by 1 MeV neutrons and 24 GeV protons with F > 1014 cm-2 (detectors developed under “Technotest” sub-project)

4. Simulation of DP E(x) profile with a consideration of carrier trapping to midgap energy levels

5. Reconstruction of E(x) profiles in MCZ Si detectors

Conclusions

E. Verbitskaya et al., 9 RD50 Workshop, CERN, Geneva, Oct 16-18, 2006

3

Models for electric field distribution in irradiated Si detectors

Standard model

Neff = const, E(x) – linear, Vfd derived from C-V curves

Valid for F 5·1013 cm-2

p+ n+

-Neff

p+ n+

-Neff

n-type Sibeyond SCSI

-Neff


4

Models for electric field distribution in heavily irradiated Si detectors

Detector: Double Junction structure:

Two depleted regions at the sides of detectors irradiated beyond SCSI, peaks of E at p+ and n+ contacts

Z. Li, H. W. Kraner, IEEE TNS 39 (1992) 577

Two depleted regions and a neutral base in-between

D. Menichelli, M. Bruzzi, Z. Li, V. Eremin, NIM A 426 (1999) 135

Two depleted regions and a base in-between with electric field due to potential drop over high resistivity bulk

E. Verbitskaya et al. Operation of heavily irradiated silicon detectors in non- depletion mode. Pres. RESMDD’05, Nucl. Instr. and Meth. A 557 (2006) 528-539

p+ n+

V2

V1

pinch

-off

V>Vfd

Wb

p+ n+

V2

V1

pinch

-off

V>Vfd

Wb

Bulk Si: n-type converts to high resistivity p-type E. Borchi, M. Bruzzi et al, IEEE Trans. Nucl. Sci. 46 (1999) 834; M. Bruzzi, IEEE Trans. Nucl. Sci. 48 (2001) 960.


5

Experimental evidence of Double Peak electric field distribution

Measurements of OBIC and surface potential in non-irradiated and irradiated detectors

Existence of two depletion layers adjacent to the contacts and separated by a layer inverted to p-type Si (close to intrinsic)

Insignificant difference in E(x) near the p+ contact in non-irradiated and irradiated Si detectors

Model of DP E(x) distribution: ionization of DLs due to band bending near the contacts

A. Castaldini, A. Cavallini, L. Polenta, F. Nava, C Canali, NIM A476 (2002) 550


6

Origin of Double Peak (DP) electric field distribution

V. Eremin, E. Verbitskaya, Z. Li. NIM A 476 (2002) 556

Trapping of free carriers from detector reverse current to Deep Levels leads to DP E(x)

trapping

-V

midgap DLs:

DD: Ev + 0.48 eV

DA: Ec – 0.52 eV


7

Approach for pulse response simulation and E(x) reconstruction with a consideration of electric field in the base

Transient current:

eff

odr Ne

Neff, Ntr = f(F)

effto ed

EQti /

p+ n+

E1

Eb

E2

W1 Wb W2

h

111 trdreff

trthtr Nv

1

Three regions of heavily irradiated detector structure are considered Reverse current flow creates potential difference and electric

field in the neutral base

Goal: reconstruction of electric field profile from current pulse response, simulation of detector DP pulse response

E. Verbitskaya et al. Pres. RESMDD’05, NIM A 557 (2006) 528-539


8

i ~ exp(-t/eff)

p+ n+

Simulation of pulse response for carrier generation from one side of detector

Signal due to carrier drift in W1 is independent on the properties of Wb and W2

i = i1 ~ exp(-t/eff)

W1, Neff1, E1

tcol

tcol: depends on Eb and Wb Eb, Wb

Charge collected inside W2

QW2

QW2 = Qo(d – W1 –Wn)/d Wb, W2, E2, Neff2

Edx = V


9

Experimental tool for study of electric field distribution

Transient Current Technique

Pulse Laser for generation of nonequilibrium carriers

Short wavelength of laser (e or h generation from one side and transport through detector bulk)


10

Experimental observations of DP current pulse response

-2.0E-05

0.0E+00

2.0E-05

4.0E-05

6.0E-05

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1.2E-04

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time (ns)

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ent

(A)

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NeutronPti_cz_d11Fn = 5e14 cm-2before anneal p+ side, RT

-1.0E-05

0.0E+00

1.0E-05

2.0E-05

3.0E-05

4.0E-05

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1.0E-04

0 5 10 15 20 25 30

time (ns)

curr

ent

(A)

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NeutronPti_cz_d115e14n+ side, RT

• Electron collection (p+ side): second peak (H2) increases with V: H1/H2 • Major junction at n+ side: SCSI:

1. 1 MeV neutron irradiation MCZ Si, Fn = 51014 cm-2


11

2. 24 GeV proton irradiation MCZ n-Si, Fp = 11015 cm-2

0.0E+00

5.0E-05

1.0E-04

1.5E-04

2.0E-04

2.5E-04

3.0E-04

0 5 10 15 20 25 30time (ns)

cu

rre

nt

(A)

36 V

76 V

120 V

205 V

246 V

303 V

322 V

350 V

protons 1e15cm-2PTI_CZ-e4p+ side

0.0E+00

5.0E-05

1.0E-04

1.5E-04

2.0E-04

2.5E-04

3.0E-04

0 5 10 15 20 25 30time (ns)

curr

ent

(A)

42 V

88 V

134 V

205 V

250 V

294 V

357 V

395 V

417 V

protons 1e15cm-2BNL_114p+ side

0.0E+00

5.0E-05

1.0E-04

1.5E-04

2.0E-04

2.5E-04

3.0E-04

0 5 10 15 20 25 30time (ns)

curr

ent

(A)

40 V

75 V

120 V

205 V

245 V

303 V

322 V

350 V

protons 1e15cm-2HIP_62p+ side

Influence of processing:difference in H1/H2

Double Peak for all detectorsat V > 200 V1st peak dominates (H1/H2>1)


12

DP response under long term annealing MCZ Si, Fp = 11015 cm-2

-5.0E-06

0.0E+00

5.0E-06

1.0E-05

1.5E-05

2.0E-05

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Proton, 1e15 cm-2Pti_cz_e4

p+ sidebefore anneal

-5.0E-06

0.0E+00

5.0E-06

1.0E-05

1.5E-05

2.0E-05

2.5E-05

0 5 10 15 20

time, nscu

rren

t, A

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proton, 1e15 cm-2PTI-CZ-e42 anneal, 25 min, t_sum = 35 min

-5.0E-06

0.0E+00

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ent,

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proton, 1e15 cm-2PTI-CZ-e43 anneal, 50 min, t_sum = 85 min

-1.0E-05

0.0E+00

1.0E-05

2.0E-05

3.0E-05

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Proton, 1e15 cm-2Pti_cz_e45 anneal, 180 min, t_sum = 355 min

-2.0E-05

0.0E+00

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Proton, 1e15 cm-2Pti_cz_e46 anneal, 6 h t_sum = 715 min

-1.0E-05

0.0E+00

1.0E-05

2.0E-05

3.0E-05

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2 7 12 17 22

time (ns)

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ent

(A)

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Proton, 1e15 cm-2Pti_cz_e47 anneal, 6 ht_sum = 1075 min

Before anneal 2: 35 min (total tann)

Tann = 80C, 7 steps

3: ~1.5 h

5: 6 h 6: 12 h 7: 18 h

V = 40-440 V

PTI-CZ-e4

• H1 and H2 rise at each step• H1/H2 changes under annealing and 1


13

Evolution of Double Peak response under annealing,MCZ Si, Fp = 11015 cm-2

Annealing of DP response

0

0.2

0.4

0.6

0.8

1

1.2

0 5 10 15 20time (ns)

cu

rre

nt

no

rma

lize

d

0

10

35

85

175

355

715

1075

t_ann (min):BNL-114Fp = 1e15 cm-2V = 420 V

Normalized response


0

0.2

0.4

0.6

0.8

1

1.2

0 5 10 15 20 25 30time (ns)

curr

ent

no

rmal

ized

0

1: 10

2: 35

3: 85

4: 175

5: 355

6: 715

7: 1075

t_ann (min):

PTI_cz_e4Fp = 1e15 cm-2V = 300 V

eff doesn’t change under annealing


14

Amplitude ratio H1/H2 under annealingMCZ Si, Fp = 11015 cm-2

Annealing of DP response; Fp = 1e15 cm-2

0

1

2

3

4

5

6

0 200 400 600 800 1000 1200t_ann (min)

H1

/H2

PTI-CZ-e4, 300 V

BNL-CZ-114, 420 V

Stages of DP shape non-monotonous changes: 1. increase of H1

2. increase of H2

shape tends to single peak (E(x) linear) at tann = 1.5-6 h3. reduction of H2 and increase of pulse width


15

Comparison between n and p: amplitude ratio H1/H2 in DP response

0

5

10

15

20

25

0 100 200 300 400 500 600V (Volt)

H1/

H2

PTI-CZ-e4

BNL-CZ-114

PTI-CZ-d11

BNL-CZ-98

p

n

≤1

Fluence:Fn = 51014 cm-2

Fp = 11015 cm-2


16

Fn = 5e13 cm-2, PTI-Cz-c12, n+ side, RT

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

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0.9

1

1.1

0 100 200 300 400 500 600 700 800 900 1000V (Volt)

Q_n

orm

before anneal

6 min

16 min

36 min

76 min

PTI-Cz-d11, RT

0

0.2

0.4

0.6

0.8

1

1.2

0 200 400 600 800 1000V (Volt)

Q_n

orm

Q_total

Q(20 ns)

Q(10 ns)

Q_total

Q (20 ns)

Q(10 ns)

before anneal

156 min

5e14 cm-2

neutrons Q normalized total, Fp = 1e14 cm-2, before anneal

0

0.2

0.4

0.6

0.8

1

1.2

0 100 200 300 400 500 600

V (Volt)

Q n

orm

aliz

ed PTI_cz-d3BNL_101HIP_21PTI_FZ_b3

protons

Q normalized total, Fp = 1e15 cm-2, before anneal

0

0.2

0.4

0.6

0.8

1

1.2

0 100 200 300 400 500V (Volt)

Q n

orm

iliz

ed

PTI_cz-e4

BNL_114

HIP_62

# BNL-114, Fp = 1e15 cm-2, anneal 1075 min

0

0.2

0.4

0.6

0.8

1

0 100 200 300 400 500

V (Volt)

Q n

orm

aliz

ed

Q total

Q(20 ns)

Q(10 ns)

Comparison: MCZ Si, Q(V)

Single peak

Double peak

1e15 cm-2

5e13 cm-21e14 cm-2

annealing

17

for neutrons and protons, TCT data

FZ, n: 0.022

MCZ, n: 0.017MCZ, p: 0.0045 Z. Li et al. Radiation hardness of high

resistivity magnetic Czochralski silicon detectors after gamma, neutron,

and proton radiations, TNS- 51 (2004) 1901-1908

Experimental data on Neff(F) and Vfd dependence in MCZ Si detectors

0

50

100

150

200

250

300

1.0E+13 1.0E+14 1.0E+15

24 GeV/c Proton Fluence [p/cm2]

Vfd

[V

]

V_dep(QVe) V_dep(QVh)

A. Bates and M. Moll. A comparison between irradiated Magnetic Czochralski and Float Zone silicon detectors using the Transient Current Technique. NIM A 555 (2005) 113

Depletion voltage has passed its minimum value without type inversion


18

E(x) profile in MCZ Si detectors irradiated by 24 GeV protons (earlier results)

Pulse response fit and E(x) reconstruction basing on three region structure Fp = 2.21015 cm-2 Electron collection (p+ side) SMART detector

M. Scaringella et al. Localized energy levels generated in Magnetic Czochralski silicon by proton irradiation and their influence on the sign of space charge density. NIM A, in press; and N. Manna, pres. 8 RD50 Workshop, June 25-28, 2006, Prague

Wide region with positive space charge!

“Puzzle” – Space Charge Signin MCZ Si irradiated by 24 GeVprotons??


19

Simulation of DP E(x) profile with a consideration of carrier trapping to midgap energy levels:

E(x) and Neff(x) vs. V

Parameters:

introduction rate of generation centers mj

introduction rate of midgap deep levels, DA and DD concentration ratio k = NDA/NDD

bias voltage V temperature T detector thickness d initial resistivity (shallow donor concentration No)

midgap DLs: DD: Ev + 0.48 eV simulation is based on

DA: Ec – 0.52 eV Shockley-Read-Hall statistics


20

Simulation: Evolution of Double Peak E(x) at various NDA/NDD

Fn = 51014 cm-2

V: 100-1000 VNo = 11012 cm-3

d = 300 m, RT

0.0E+00

1.0E+04

2.0E+04

3.0E+04

4.0E+04

5.0E+04

6.0E+04

7.0E+04

0 0.005 0.01 0.015 0.02 0.025 0.03x (cm)

E(x

) (V

/cm

)

100 V

200 V

300 V

400 V

500 V

600 V

800 V

1000 V

k = 1.2

0.0E+00

1.0E+04

2.0E+04

3.0E+04

4.0E+04

5.0E+04

6.0E+04

7.0E+04

0 0.005 0.01 0.015 0.02 0.025 0.03x (cm)

E (

V/c

m)

100 V

200 V

300 V

400 V

500 V

600 V

800 V

1000 V

k = 1

0.0E+00

1.0E+04

2.0E+04

3.0E+04

4.0E+04

5.0E+04

6.0E+04

7.0E+04

0 0.005 0.01 0.015 0.02 0.025 0.03x (cm)

E (

V/c

m)

100 V

200 V

300 V

400 V

500 V

600 V

800 V

1000 V

k = 0.8


21

E(x) and Neff vs. VFn = 51014 cm-2

0.0E+00

1.0E+04

2.0E+04

3.0E+04

4.0E+04

5.0E+04

6.0E+04

7.0E+04

0 0.005 0.01 0.015 0.02 0.025 0.03x (cm)

E (

V/c

m)

100 V

200 V

300 V

400 V

500 V

600 V

800 V

1000 V

k = 1

-1.5E+13

-1E+13

-5E+12

0

5E+12

0 0.005 0.01 0.015 0.02 0.025 0.03

x (cm)

Ne

ff (

cm

-3)

200 V

300 V

400 V

500 V

600 V

800 V

1000 V

k = 1RT

Neff is vastly non-uniform and E is non-linear even at maximal V of 1000 V


22

Evolution of Double Peak E(x) vs. NDA/NDD

Fn = 51014 cm-2

MCZ Si No = 3.51012 cm-3 d = 300 mm, RT

0.0E+00

1.0E+04

2.0E+04

3.0E+04

4.0E+04

5.0E+04

6.0E+04

7.0E+04

8.0E+04

0 0.005 0.01 0.015 0.02 0.025 0.03x (cm)

E (

V/c

m)

100 V

200 V

300 V

400 V

500 V

600 V

800 V

1000 V

k = 1.5

E at p+ contact changes insignificantly: correlates to neutron irradiation

0.0E+00

1.0E+04

2.0E+04

3.0E+04

4.0E+04

5.0E+04

6.0E+04

7.0E+04

0 0.005 0.01 0.015 0.02 0.025 0.03x (cm)

E (

V/c

m)

100 V

200 V

300 V

400 V

500 V

600 V

700 V

800 V

k = 0.5

Major junction at p+ side:correlates to proton irradiation


23

Experimental results: current response fit and E(x) reconstruction in MCZ Si detectors

Goal:

simulation/fit of detector DP pulse response,

reconstruction of electric field profile from current pulse shape,

considering detector structure with three regions: W1, Wb and W2


24

E(x) reconstruction and adjustment to midgap level modelNeutrons, Fn = 51014 cm-2, MCZ Si

0

20

40

60

0 5 10 15 20time (ns)

Cu

rren

t (u

A)

experiment

fit

V = 285 V

Parameters derived by adjustment:

mj = 0.7 cm-1

DD Ev + 0.48 eV 5·1014 cm-3

DA Ec - 0.52 eV 6.75·1014 cm-3

k = 1.350.0E+00

5.0E+03

1.0E+04

1.5E+04

2.0E+04

2.5E+04

3.0E+04

3.5E+04

0 0.005 0.01 0.015 0.02 0.025 0.03x (cm)

E (

V/c

m)

E(x) reconstructionadjustment

285 V

E(x) reconstruction

0.0E+00

1.0E+04

2.0E+04

3.0E+04

4.0E+04

5.0E+04

0 0.005 0.01 0.015 0.02 0.025 0.03x (cm)

E (

V/c

m)

236 V

285 V

334 V

PTI-CZ-d11

At high Fn and V negative SCR extends inside detector bulk


25

Reconstruction of E(x) from DP response:influence of processing

p+ n+

E1

Eb

E2

W1 Wb W2

Electric field gradient dE/dx and Neff in the region adjacent to p+ contact are differentand sensitive to detector processing

HIP-CZ-66 PTI-CZ-C11

tau_e (ns) 4 5Neff1 (c m-3) 1.41E+11 1.09E+12Neff2 (c m-3) 9.46E+12 9.51E+12E_b (V/ c m) 500 1500

Fn = 51014 cm-2 p+


26

Reconstruction of E(x) from DP response:Protons, Fp = 11015 cm-2, MCZ Si + annealing

PTI-CZ-e4, Fp = 1e15 cm-2

0.0E+00

5.0E+03

1.0E+04

1.5E+04

2.0E+04

2.5E+04

3.0E+04

3.5E+04

4.0E+04

4.5E+04

0 0.005 0.01 0.015 0.02 0.025 0.03x (cm)

E (

V/c

m)

before anneal

35 min

715 min

1075 min

300 V


0

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1

1.2

0 5 10 15 20 25 30time (ns)

cu

rre

nt n

orm

aliz

ed

0

1: 10

2: 35

3: 85

4: 175

5: 355

6: 715

7: 1075

t_ann (min):

PTI_cz_e4Fp = 1e15 cm-2V = 300 V

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0.0E+00

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ent

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Proton, 1e15 cm-2Pti_cz_e4

p+ sidebefore anneal


0.0E+00

5.0E+03

1.0E+04

1.5E+04

2.0E+04

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3.0E+04

0 0.005 0.01 0.015 0.02 0.025 0.03x (cm)

E (

V/c

m)

200 V

360 V

200 V

360 V

annealing


27

E(x) reconstruction and adjustment to midgap level model Fp = 51014 cm-2, MCZ Si, PTI-CZ-e4


0.0E+00

5.0E+03

1.0E+04

1.5E+04

2.0E+04

2.5E+04

3.0E+04

0 0.005 0.01 0.015 0.02 0.025 0.03x (cm)

E (

V/c

m)

reconstruction

adjustment

360 V

mj = 0.7 cm-1 – like for neutrons

DD Ev + 0.48 eV 6.6·1014 cm-3

DA Ec - 0.52 eV 3·1014 cm-3

k = 0.45

Parameters derived by adjustment:

k(n)/k(p) 3

correlates to (n)/(p) 4


28

-2.0E-05

0.0E+00

2.0E-05

4.0E-05

6.0E-05

8.0E-05

1.0E-04

0 5 10 15 20 25 30

time (ns)

cu

rre

nt

(A)

43V

88V

135V

205V

275V

298V

321V

367V

404V

440V

Fp = 1e15 cm-2Pti_CZ_e4Annealing 1075 minLaser to p+ side

Protons, Fp = 11015 cm-2, MCZ Si, annealing

• In MCZ Si detectors irradiated by 24 GeV protons electric field extends over entire detector thickness. The major junction is at the p+ contact and SCR is charged positively.• Under annealing E(x) profile becomes more symmetric with increasing V.

PTI-CZ-e4, Fp = 1e15 cm-2, t_ann = 1075 min

0.0E+00

1.0E+04

2.0E+04

3.0E+04

4.0E+04

5.0E+04

0 0.005 0.01 0.015 0.02 0.025 0.03x (cm)

E (

V/c

m)

300 V

400 V


29

Conclusions

Approach of E(x) distribution with a consideration of electric field in the base region allows E(x) reconstruction in detectors irradiated by high F irrespective to the irradiation type.

In heavily irradiated detectors electric field distribution is vastly non-uniform and shows double peak shape with positively and negatively charged regions. Full depletion implies that electric field extends over entire detector bulk and carrier collection is drift process.

Different balance of DDs and DAs induced by neutrons and protons results in the essential difference of E(x) profile, pulse shape and collected charge at the same bias voltage.

In neutron irradiated MCZ Si detectors E at the major junction (n+ side)

decreases with voltage that is favorable for detector operation.

In MCZ Si detectors irradiated by 24 GeV protons the major space charge region is adjacent to the p+ contact and has a positive space charge.


30

Acknowledgements

This work was supported in part by:

• RD50 collaboration,• INTAS-CERN project # 03-52-5744,• RFBR project SS # 00-15-96750

Thank you for your attention!


Documents

Electric field distribution in irradiated MCZ Si detectors