I. Pintilie a , E. Fretwurst b , A. Junkes b , G. Lindström b

NSS, 21 October 2008, Dresden 1

Radiation induced point- and cluster-related defects with strong impact to damage

properties of silicon detectors

I. Pintiliea, E. Fretwurstb, A. Junkesb, G. Lindströmb

a National Institute of Materials Physics, Bucharest, Romania

b Institute for Experimental Physics, University of Hamburg, Hamburg, Germany


Outline

Motivation Goals Electrically active centers in SCR Techniques Material & Irradiations Results

Point defects Extended defects

Summary & Conclusions


Motivation

“Defect engineering” needed for SLHC application in the tracking area to improve the detectors radiation tolerance

0 0.5 1 1.5 2 2.5 3 3.5eq [1014cm-2]

1

2

3

4

5

6

7

|Nef

f| [1

012 c

m-3]

100

200

300

400

Vde

p [V

] (

300

m)

neutronsneutrons

neutronsneutronspionspionsprotonsprotons

pionspionsprotonsprotons

oxygen rich FZ

standard FZstandard FZ

(CERN-RD48)


• None of the detected defects could explain the macroscopic behaviour of the irradiated diodes• The defect models attributed the oxygen effect to the formation of a deep acceptor (V2O complex), suppressed in oxygen rich silicon

Radiation damage – radiation induced defects

M. Moll, PhD-thesis 1999


Goals

Search for still undetected defects responsible for the radiation damage, as seen at operating temperatures Point defects, predominant after gamma and electron irradiation Extended defects (clusters), responsible for hadron damage

Understand their formation and find ways to optimize the device performance


Defect´ signature – emission rates

2) Contribution to the leakage current

1) Contribution to Neff - given by the steady state ocupancy of the defect levels in SCR

p+

n+

Electrons in the conduction band

Holes in the valence band

n

NA

ND(+)

(-)/0

Electrical properties of Point Defects in the Space Charge Region (SCR)

Tk

ETETTe

b

VCTpnpn

,,,

)(exp*)(~)(

acceptorT

donorTeff

pn

nT

donorT

pn

pT

acceptorT

nnN

TeTe

TeNTn

TeTe

TeNTn

)()(

)()(;

)()(

)()(

EC

EV

ET

))(*)()(*)((***)( 0 TnTeTnTedAqTI donorTp

acceptorTndep

NSS, 21 october 2008, Dresden 7

Charge state of electrically active defects at room temperature

Donors (+/0)

+ + + + + + + + + + + + + + + + + + + + +

EC

EV

? + + + + + + + + + + + +

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

• traps for electrons• show Poole-Frenkel effect• Contribute with (+) to Neff at RT

• traps for holes• show no Poole-Frenkel effect• do not contribute to Neff at RT unless are near the midgap

P

CiOi

Ei


Acceptors (0/-)

? - - - - - - - - - - - -

EC

EV

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

• traps for electrons• show no Poole-Frenkel effect• do not contribute to Neff at RT unless are near the midgap

• traps for holes• show Poole-Frenkel effect• contribute with (-) to Neff at RT

B

VO, V2

Charge state of electrically active defects at room temperature

Ei


Techniques

W(0) x0

0

metal n-semiconductorq qVbi

q(V -V)b iq

E FM

E FMECEFnETEV

ECEFETEVenergy

x

W(0)-without biasthermal equilibrium

with reverse biastransition from a nonstationary state to a stationary oneW(V)W(V)- W'W'-

I) Deep Level Transient Spectroscopy - for NT < 10% Nd

- based on measuring capacitance transients: ΔC = ΔC0 exp(-en,pt)

► emission rates - en,p(T) - position in the bandgap - ΔET - capture cross sections - n , p ► defect concentration: NT ~ 2·Nd·ΔC/C0

II) Thermally Stimulated Currents Method – improved for NT > Nd and for centers with enhanced field emission

- based on measuring the current due to emission from the filled traps

► emission rates - en,p(T) - position in the bandgap - ΔET - apparent capture cross sections - n , p ► defect concentration: NT


Material & Irradiations

Irradiations• Co60 -source at BNL, dose range 1 to 500 Mrad• 6 -15 MeV electrons: irradiation facility at KTH Stockhom, Sweden • 23 GeV protons: irradiation facility at CERN- 1 MeV neutrons: TRIGA reactor in Ljubljana/Slovenia

Material• Float zone- Silicon wafers: <111>, 300 μm, 3-4 kcm, Nd~1012 cm-3

- standard Oxidation (STFZ) - Nd~8x1011 cm-3 - difussion oxygenated (72 h at 1150 C) (DOFZ) Nd~1.2x1012 cm-3

• MCz-Silicon wafers: <100>, 300 μm, 870 cm, Nd = 4.94x1012 cm-3

• EPI-Silicon wafers: <111>• 25 and 50 μm on 300 μm Cz-substrate, 50 cm, Nd~7.2x1013 cm-3 • 75 μm on 300 μm Cz-substrate, 169 cm

- standard Oxidation (EPI-ST), Nd = 2.66x1013 cm-3

- diffusion oxygenated for 24 h/1100°C (EPI-DO) Nd = 2.48x1013 cm-3


0 200 400 600 800 1000dose [Mrad]

0

50

100

150

Vde

p [V

]

0

5

10

15

20

25

Nef

f [10

11 c

m-3

]

CA: FZ standardCA: FZ standardCB: DOFZ 24 h/11500CCB: DOFZ 24 h/11500CCC: DOFZ 48 h/11500CCC: DOFZ 48 h/11500CCD: DOFZ 72 h/11500CCD: DOFZ 72 h/11500C

Results – Point Defects (Ref. 1-6)

Co60- irradiation – only point defects are generated

Very pronounced beneficial effect of oxygen on both I and Vdep

Close to midgap acceptor correlated with [O] responsible ?

STFZ

DOFZSTFZ

DOFZ


- Low irradiation doses (but already high for DLTS)

Ip center

deep acceptor (-/0)

Ea = Ec – 0.545 eV n = (1.70.2)x10-15 cm2

- direct measurement p = (91)x10-14 cm2

- from NTDLTS(T)

~ 90% occupied with (-) at RT

220 230 240 250 260 270 280 290 300

0

2

4

6

8

10 TW

= 200 ms

IE

42.55 Mrad dose STFZ DOFZ

DLT

FS s

igna

l - b

1 co

ef. (

fF)

Temperature (K)

STFZ

DOFZ


- Higher irradiation doses (TSC)

20 40 60 80 100 120 140 160 180 200

0

10

20

30

40

Ip

+/0

CiO

i

+/0

VO-/0 + CiC

s

Ip

0/-

96 Mrad 190 Mrad 245 Mrad 284 Mrad 360 Mrad 500 Mrad

TS

C s

igna

l (pA

)

Temperature (K)

Ip

Ip centers – Two levels in the gap: - a donor Ev+0.23eV (+/0) & an acceptor Ec-0.545 eV (0/-) - Supressed in Oxygen rich material and Quadratic dose dependence generated via a 2nd order process ( V2O?) 1) V+O VO

2) V+VO V2O

DOFZ

STFZ

STFZ


BD center – bistability and donor activity

20 40 60 80 100 120 140 160 180 200

0.1

1

10

100 BD

Ip

/-CiOi+/0

BD(98K)

VO-/0

E(50K)H(42K)

DOFZ - 245 Mrad: Cooling from RT under 0 V after: exposure to day light keeping in dark at RT for 2 days

TSC

sig

nal (

pA)

Temperature (K)

BD center – donor in the upper part of the gap (+ at RT)- generated in oxygen rich material - after C060- irradiation, can even overcompensate the effect of deep acceptors!

• In low doped n-type DOFZ

20 40 60 80 100 120 140 160 180 2000

2

4

6

8

10

12

14

[BD] = 8x1011 cm-3

EPI-DO, 5x1013 cm-2 (1MeV neutrons)

(0/++)(+/++)

BD

TS

C s

ign

al (

pA

)

Temperature (K)

as irradiated 3 h at 295K

• In medium doped n-type EPI-DO

Ei BD(98K) = Ec- 0.225 eV (0/++ ) ; Ei

BD(50K) = Ec- 0.15 eV (+/++ )

The bistability, donor activity and energy levels associate the BD centers with TDD2 oxygen dimers are part of the defect structure


Impact of Ip and BD defects on detector properties

0 50 100 150 200 250 300 350 400 450 500 550

0

100

200

300

400

500

600

700

800

900

1000293Kfrom I - V

DOFZ STFZ

calculated (I level) DOFZ (errors > 5%) STFZ (errors < 5%)

I (

nA

)Co60- gamma irradiation dose

)()( TnTN Teff

0 50 100 150 200 250 300 350 400 450 500 550 600

-2.0x1012

-1.5x1012

-1.0x1012

-5.0x1011

0.0

from C-V DOFZ STFZ

calculated (Ip and BD)

DOFZ (errors > 5%) STFZ (errors < 5%)

Nef

f (c

m-3)

Co60- gamma irradiation dose

VolTnTeqTI Tn )()()( 0

first breakthrough in understanding the damage effects

STFZ

DOFZ

DOFZ

STFZ

change of Neff and leakage current well described


Results – Extended Defects (clusters) (Ref. 7) After irradiation with 1 MeV neutrons, Ф= 5x1013 cm-2

1 10 100 1000 100000

1x1012

2x1012

3x1012

4x1012

5x1012

6x1012

Def

ect c

once

ntra

tions

cm

-3

Annealing time at 80 0C

H(116K) H(152K) H(140K) all H centers E(30K)

• H(116K), H(140K) and H(152K) traps for holes• E(30K) trap for electrons

• H(116K) was detected previously• H(152K) ~ was attributed so far to CiOi

0 20 40 60 80 100 120 140 160 180 200

0

5

10

15

20

25

H(140K)

BDB

EPI-DO

H(40K) H(116K)BDA

V2+?

H(152K)

VO

E(30K)

E(28K)

TS

C s

ign

al (

pA)

Temperature (K)

Forward injection at 5K, RB=150V as irradiated 20min@80C 80min@80C 1370min@80C 34270min@80C

Electron injection at 5K 1370min@80C

Independent on the material


23 GeV protons

1 10 100 1000 10000

0.0

3.0x1012

6.0x1012

9.0x1012

1.2x1013

1.5x1013

1.8x1013

2.1x1013

2.4x1013

2.7x1013

3.0x1013

3.3x1013

De

fect

Con

cen

trat

ion

(cm

-3)

Annealing time at 80 0C (min)

H116K H140K H152K acceptors E30K

EPI-DO 75 m, eq=2.33x1014 cm-2

EPI-DO, 75 m, Фeq= 2.33x1014 cm-2

0 20 40 60 80 100 120 140 160 180 200

0

30

60

90

120

H(152K)

H(140K)

TS

C s

ign

al (

pA

)

Temperature (K)

EPI-DO 75 m Fw- as irradiated Fw - 20min Fw - 80 min Fw - 160 min Fw - 320 min Fw - 640 min Fw - 1280 min Fw - 2810 min Fw - 5700 min Fw - 11460 min Fw - 16980 min

H(116K)

?V2

BDA

0/++

VO

H(40K)

E(30K)

The generation of E(30K) center is much enhanced relative to of the H centers !


H(116K), H(140K), H(152K) and E(30K) - cluster related traps with enhanced field emission

90 100 110 120 130 140 150 160 170 180 190

0

5

10

15Forward injection at 5K

T = 3.5K

H(140K)0/-BD0/++

H(116K)0/-

T = 2.5K T = 5.3K

EPI-DO irradiated with 1 MeV neutrons, = 5x1013cm-2

T = 6K

H&E trapsH(152K)0/-

TS

C s

ign

al (

pA

)

Temperature (K)

250V 200V 150V 100V 70V 3D-PF, 250 V 3D-PF, 200V 3D-PF, 150V 3D-PF, 100V 3D-PF, 70V

Ei116K = Ev + 0.33eV, p

116K =410-14 cm2

Ei140K = Ev + 0.36eV, p

140K =2.510-15 cm2

Ei152K = Ev + 0.42eV, p

152K =2.310-14 cm2

Ei30K = Ec - 0.1eV, n

30K =2.310-14 cm2

0 10 20 30 40 50 60 70 800

20

40

60

80

100

120

140

BDB

+/++

EPI-DO 75 m, irradiated with 23GeV protonseq=2.33x1014 cm-2

TS

C s

ign

al (

pA

)

Temperature (K)

11460min@80C 50 V 100 V 150 V 200 VE(30K)

VO

•The 3D-Poole Frenkel effect formalism describes the experiments

Are acceptors in the lower part of the gap and contribute with (-) space charge at RT

Are donors in the upper part of the gap and contribute with (+) space charge at RT


EPI-ST: Nd = 2.66x1013 cm-3; EPI-DO: Nd = 2.48x1013 cm-3; MCz: Nd = 4.94x1012 cm-3

The impact of BD, E(30K), H(116K), H(140K) and H(152K) on Neff

1 10 100 1000 10000-5.0x1012

0.0

5.0x1012

1.0x1013

1.5x1013

2.0x1013

2.5x1013 from C-V at RT from TSC

1 MeV neutrons, Ф= 5x1013 cm-2

0.1 1 10 100 1000 100004x1011

5x1011

6x1011

7x1011

8x1011

9x1011

[BD

] (c

m-3)

Annealing time at 80 0C (minutes)

EPI-DO EPI-ST MCz

Differences between materials given by the initial doping (Nd) and [BD], only!

These are the defects responsible for the annealing of Neff at RT!


75 µm EPI-DO, 23 GeV p-irradiation, eq = 2.3E14/cm²

0.0E+00

5.0E+12

1.0E+13

1.5E+13

2.0E+13

2.5E+13

1.0E-01 1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05

annealing time @ 80°C [min]

Nef

f =

Nef

f0-N

eff(

,t)

[1/

cm³]

macr. measured (C/V)

macr. predicted (TSC)

donor generation large:2.1E13/cm³, g = 9.0E-2/cm

75 µm EPI-DO, 1 MeV-eq. n-irradiation, eq = 5.0E13/cm²

0.0E+00

2.0E+12

4.0E+12

6.0E+12

8.0E+12

1.0E+13

1.0E-01 1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05

annealing time @ 80C [min]

N

eff =

Nef

f0 -

Nef

f(

,t)

[1/c

m³]

macr. measured (C/V)

macr. predicted (TSC)

donor generation small:9.0E11/cm³, g = 1.8E-2/cm

Larger donor generation (E(30K) and BD) after 23GeV protons than after 1 MeV neutrons (~4.5 times) !

EPI-DO 75 m: Nd = 2.48x1013 cm-3

23GeV protons, Фeq= 2.33x1014 cm-21 MeV neutrons, Ф = 5x1013 cm-2


Summary – defects with strong impact on the device properties at operating temperature

Point defects

EiBD = Ec – 0.225 eV

nBD =2.310-14 cm2

EiI = Ec – 0.545 eV n

I =2.310-14 cm2

pI =2.310-14 cm2

Cluster related centers

Ei116K = Ev + 0.33eV

p116K =410-14 cm2

Ei140K = Ev + 0.36eV

p140K =2.510-15 cm2

Ei152K = Ev + 0.42eV

p152K =2.310-14 cm2

Ei30K = Ec - 0.1eV

n30K =2.310-14 cm2

V2 -/0

VO -/0 P 0/+

H152K 0/-

H140K 0/-

H116K 0/-CiOi

+/0

BD 0/++

Ip 0/-

E30K 0/+

B 0/-

0 charged at RT

+/- charged at RT

Point defects extended defects


Conclusions Direct correlation between defect investigations

and device properties can be achieved!

Point defects – dependent on the material defect engineering does work

Cluster related defects – independent on the material Possibility of compensation with point defects via defect engineering


Acknowledgements

Alexander von Humboldt Foundation University of Hamburg Zheng Li for Co60 - gamma irradiations at BNL Gregor Kramberger for 1 MeV neutron irradiations

at Triga reactor Ljubljana Maurice Glasser for 23GeV proton irradiations CiS, Erfurt, for processing the diodes

References

1) I. Pintilie, E. Fretwurst, G. Lindstroem and J. Stahl, APPL. PHYS. LETT. 81 (1): 165-167 JUL 1 (2002)2) I. Pintilie, E. Fretwurst, G. Lindstroem and J. Stahl, APPL. PHYS. LETT. 83 (15): 3216-3216 OCT 13 (2003) 3) I. Pintilie, E. Fretwurst, G. Lindstroem and J. Stahl, NUCL. INSTR. & METH. IN PHYS. RES. 514 (1-3): 18-24 (2003) 4) I.Pintilie, E. Fretwurst, G. Kramberger, G. Lindstroem, Z. Li, J. Stahl, PHYSICA B-CONDENSED MATTER 340: 578, (2003)5) I. Pintilie , M. Buda, E. Fretwurst, G. Lindstroem and J. Stahl, NUCL. INSTR. & METH. IN PHYS. RES. 556 (1): 197-208 (2006) 6) E. Fretwurst, et al NUCL. INSTR. & METH. IN PHYS. RES. 583 (1), 58-63, (2007)7) I. Pintilie, E. Fretwurst, G. Lindstroem, Appl. Phys. Lett. 92, 024101 (2008)

Documents

I. Pintilie a , E. Fretwurst b , A. Junkes b , G. Lindström b