i. pintilie a , e. fretwurst b , a. junkes b , g. lindström b
DESCRIPTION
Radiation induced point- and cluster-related defects with strong impact to damage properties of silicon detectors. I. Pintilie a , E. Fretwurst b , A. Junkes b , G. Lindström b. a National Institute of Materials Physics, Bucharest, Romania - PowerPoint PPT PresentationTRANSCRIPT
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
NSS, 21 October 2008, Dresden 2
Outline
Motivation Goals Electrically active centers in SCR Techniques Material & Irradiations Results
Point defects Extended defects
Summary & Conclusions
NSS, 21 October 2008, Dresden 3
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)
NSS, 21 October 2008, Dresden 4
• 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
NSS, 21 October 2008, Dresden 5
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
NSS, 21 October 2008, Dresden 6
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
NSS, 21 October 2008, Dresden 8
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
NSS, 21 October 2008, Dresden 9
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
NSS, 21 October 2008, Dresden 10
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
NSS, 21 October 2008, Dresden 11
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
NSS, 21 October 2008, Dresden 12
- 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
NSS, 21 October 2008, Dresden 13
- 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
NSS, 21 October 2008, Dresden 14
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
NSS, 21 October 2008, Dresden 15
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
NSS, 21 October 2008, Dresden 16
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
NSS, 21 October 2008, Dresden 17
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 !
NSS, 21 October 2008, Dresden 18
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
NSS, 21 October 2008, Dresden 19
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!
NSS, 21 October 2008, Dresden 20
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
NSS, 21 October 2008, Dresden 21
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
NSS, 21 October 2008, Dresden 22
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
NSS, 21 October 2008, Dresden 23
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)