“non-traditional methods of material properties and defect ...€¦ · workshop on defect...
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![Page 1: “Non-traditional methods of material properties and defect ...€¦ · Workshop on Defect Analysis in Radiation Damaged Silicon Detectors, Hamburg, 23./24. August 2006 J. Vaitkus](https://reader036.vdocuments.us/reader036/viewer/2022071016/5fcfb963f2fc73688e6e9112/html5/thumbnails/1.jpg)
Workshop on Defect Analysis in Radiation Damaged Silicon Detectors, Hamburg, 23./24. August 2006 J. Vaitkus
“Non-traditional methods of material properties and defect parameters
measurement
Juozas Vaitkus on behalf of a few Vilnius groups
Vilnius University, Lithuania
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Workshop on Defect Analysis in Radiation Damaged Silicon Detectors, Hamburg, 23./24. August 2006 J. Vaitkus
Outline:• Definition of aims• Photoconductivity kinetics• Free carrier diffusion and capture process
measurement • Photo-Hall and magnetoresistance• Photo-ionization spectroscopy
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Workshop on Defect Analysis in Radiation Damaged Silicon Detectors, Hamburg, 23./24. August 2006 J. Vaitkus
A few general words:
• Profile of our group “self-formed” 40 years ago as: “measurement of properties of high resistivity and wide bandgap materials”.
• These materials have many different type of local levels and, usually, different non-uniformities.
• Therefore it was developed or modified a few of methods for exclusion or activation of a definite level or non-uniformity.
• The modification of methods was oriented on:– Exclusion of an origins of nonlinearities;– Avoiding an influence of contacts;– Creation of scenario that allows to understand the process.
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Workshop on Defect Analysis in Radiation Damaged Silicon Detectors, Hamburg, 23./24. August 2006 J. Vaitkus
Free carrier kinetics
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Workshop on Defect Analysis in Radiation Damaged Silicon Detectors, Hamburg, 23./24. August 2006 J. Vaitkus
Direct measurement of trapping and recombination:photoconductivity decay (short pulse excitation)
1 23
4
EC
EV
EM
ER
1 τM=1/γnM(M-m)2 τN=1/γnMΝCM
ΘI = 1/[γnMΝCM + γnM(M-m)]ΘII = 1/[γnMΝCM]
3 τR=1/γnR(R-r)4 τP=1/γpR r
( ) ⎟⎟⎠
⎞⎜⎜⎝
⎛
+−
+= 20
01nN
mM
CMRasymp ττ
Measurement of this dependence:
E.Gaubas talk!
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Workshop on Defect Analysis in Radiation Damaged Silicon Detectors, Hamburg, 23./24. August 2006 J. Vaitkus
Limitations and possibilities
• Excitation pulse duration: ~10 ps, ~10 ns and longer pulses or mosulated dc light.
• Generation of carriers – direct band-band or extrinsic (via deep levels or from/to deep level)
• Problems appears in high quality samples due to influence of the recombination at the surface (if the diffusion is significant)
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Workshop on Defect Analysis in Radiation Damaged Silicon Detectors, Hamburg, 23./24. August 2006 J. Vaitkus
Transient gratings
• Free carriers change the refractive index of semiconductor, therefore if the excitation is by the light interference pattern, then semiconductor become as a periodical grating.
• The incident or probe beam pulse will diffract in it.
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Workshop on Defect Analysis in Radiation Damaged Silicon Detectors, Hamburg, 23./24. August 2006 J. Vaitkus
Transient gratings - contactless, non-destructive semiconductor
homogeneity controlparameters (D, S, τ and etc.) measurement method
Iλ sampleI-1
I
Λ I+1
I0
Also allows to indicate the internal electric field related to impurities if the optical symmetry allows the effect.
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Workshop on Defect Analysis in Radiation Damaged Silicon Detectors, Hamburg, 23./24. August 2006 J. Vaitkus
![Page 10: “Non-traditional methods of material properties and defect ...€¦ · Workshop on Defect Analysis in Radiation Damaged Silicon Detectors, Hamburg, 23./24. August 2006 J. Vaitkus](https://reader036.vdocuments.us/reader036/viewer/2022071016/5fcfb963f2fc73688e6e9112/html5/thumbnails/10.jpg)
Workshop on Defect Analysis in Radiation Damaged Silicon Detectors, Hamburg, 23./24. August 2006 J. Vaitkus
Two step excitation spectroscopy: generation of carriers via deep centers
0 50 100 150 200 250 300
10-5
10-4
10-3
10-2
10-1
Ι0 = 0.7 mJ/cm2
-p 17 (irradiated) -p 17 Reference
Ι0 = 0.7 mJ/cm2
-p 17 (irradiated) -p 17 Reference
Diff
. Eff
icie
ncy
a. u
.
Temperature, K
SiG.G.Macfarlane et al, J.Phys.Chem.Solids8,(1959) 388-392.
Identification if the centre is localized or Hydrogen-type
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Workshop on Defect Analysis in Radiation Damaged Silicon Detectors, Hamburg, 23./24. August 2006 J. Vaitkus
Free carrier lifetime (trapping time and diffusion) measurement by transient grating method
Iλ sampleI-1
I
Λ I+1
I0
DRG
⋅Λ⋅
+= 2
2411 πττ
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Workshop on Defect Analysis in Radiation Damaged Silicon Detectors, Hamburg, 23./24. August 2006 J. Vaitkus
0 500 1000 1500
10-2
10-1
100
0 500 1000 1500Delay (ps)
Λ = 4.0 µmτ
G = 1900 ps
Λ = 4.4 µmτ
G = 740 ps
Λ = 4.9 µmτ
G = 480 ps
Λ = 5.8 µmτ
G = 400 ps
Λ = 9.5 µmτ
G = 300 ps
Iexcitation = 5 mJ/cm2
Diff
ract
ion
effic
ienc
y (a
. u.)
Delay (ps)
Λ = 4.0 µmτ
G = 1310 ps
Λ = 4.4 µmτ
G = 640 ps
Λ = 4.9 µmτ
G = 440 ps
Λ = 5.8 µmτ
G = 370 ps
Λ = 9.5 µmτ
G = 300 ps
Si (CE2419) Si (CH2259)Iexcitation = 5 mJ/cm2
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Workshop on Defect Analysis in Radiation Damaged Silicon Detectors, Hamburg, 23./24. August 2006 J. Vaitkus
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Workshop on Defect Analysis in Radiation Damaged Silicon Detectors, Hamburg, 23./24. August 2006 J. Vaitkus
200 400 600 800 1000 1200
0,1
1
200 400 600 800 1000 1200
0,1
1
CE 2419, ( phi_p [cm-2] 1.06 x 1014), τR > 15 ns
CE 2437, ( phi_p [cm-2] 1.84 x 1014), τR > 15 ns
CE 2458, ( phi_p [cm-2] 4.25 x 1014), τR = 11 ns
Delay time (ps)
Diff
ract
ion
effic
ienc
y. (a
. u.)
Delay time (ps)
CE 2459, ( phi_p [cm-2] 6.36 x 1014), τR = 9 ns CH 2259, ( phi_p [cm-2] 9.80 x 1014), τR = 6 ns
CH 2253, ( phi_p [cm-2] 6.36 x 1014), τR = 7 ns
CH 2237, ( phi_p [cm-2] 4.25 x 1014), τR = 9 ns
CH 2219, ( phi_p [cm-2] 1.84 x 1014), τR > 15 ns
CH 2210, ( phi_p [cm-2] 1.06 x 1014), τR > 15 ns
I0 = 0.2 mJ/cm2, grating period Λ = 60 µm (decay time ~ recombination (trapping) time)
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Workshop on Defect Analysis in Radiation Damaged Silicon Detectors, Hamburg, 23./24. August 2006 J. Vaitkus
200 300 400 500 600 700
0,01
0,1
1
200 300 400 500 600 700 800 900 1000 1100 1200
1E-3
0,01
0,1
1
CE 2419,( phi_p [cm-2] 1.06 x 1014),τG = 370 ps, D = 17.6 cm2/s
CE 2437,( phi_p [cm-2] 1.84 x 1014),τG = 395 ps, D = 16.5 cm2/s
CE 2458,( phi_p [cm-2] 4.25 x 1014),τG = 390 ps, D = 16.3 cm2/s
Delay time (ps)
Diff
ract
ion
effic
ienc
y. (a
. u.)
Delay time (ps)
CE 2459,( phi_p [cm-2] 6.36 x 1014),τG = 390 ps, D = 16.2 cm2/s
I0 = 0.12 mJ/cm2 I0 = 0.25 mJ/cm2
CE 2419,( phi_p [cm-2] 1.06 x 1014),τ
G = 450 ps, D = 14.4 cm2/s
CE 2437,( phi_p [cm-2] 1.84 x 1014),τG = 455 ps, D = 14.2 cm2/s
CE 2458,( phi_p [cm-2] 4.25 x 1014),τG = 445 ps, D = 14.2 cm2/s
CE 2459,( phi_p [cm-2] 6.36 x 1014),τG = 440 ps, D = 14.2 cm2/s
200 300 400 500 600 700 800
1E-3
0,01
0,1
1
100 200 300 400 500 600 700 800 900 1000 1100 1200 1300
1E-3
0,01
0,1
1
I0 = 0.12 mJ/cm2
Delay time (ps)
Diff
ract
ion
effic
ienc
y. (a
. u.)
Delay time (ps)
I0 = 0.25 mJ/cm2
CH 2259,( phi_p [cm-2] 9.80 x 1014),τG = 380 ps, D = 16.2 cm2/s
CH 2253,( phi_p [cm-2] 6.36 x 1014),τG = 360 ps, D = 17.4 cm2/s
CH 2237,( phi_p [cm-2] 4.25 x 1014),τG = 385 ps, D = 16.4 cm2/s
CH 2219,( phi_p [cm-2] 1.84 x 1014),τG = 400 ps, D = 16.2 cm2/s
CH 2210,( phi_p [cm-2] 1.06 x 1014),τG = 400 ps, D = 16.3 cm2/s
CH 2259,( phi_p [cm-2] 9.80 x 1014),τG = 440 ps, D = 13.9 cm2/s
CH 2253,( phi_p [cm-2] 6.36 x 1014),τG = 430 ps, D = 14.4 cm2/s
CH 2237,( phi_p [cm-2] 4.25 x 1014),τG = 445 ps, D = 14.1 cm2/s
CH 2219,( phi_p [cm-2] 1.84 x 1014),τG = 470 ps, D = 13.7 cm2/s
CH 2210,( phi_p [cm-2] 1.06 x 1014),τG = 460 ps, D = 14.1 cm2/s
Rτ
Grating period Λ = 5 µm (diffusion influence).
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Workshop on Defect Analysis in Radiation Damaged Silicon Detectors, Hamburg, 23./24. August 2006 J. Vaitkus
1 2 3 4 5 60
1
2
3
1/τ G
(ps-1
)
1/Λ (µm-2)
Si (CE2419) D = 13.6 cm2/s (∆D = 0.1 cm2/s) τR > 30 ns
Si (CH2259) D = 12.5 cm2/s (∆D = 0.1 cm2/s) τR = 5.7 ns (∆τR = 0.3 ns)
Iexcitation = 5 mJ/cm2
Excitation Si (CE2419) Si (CE2459) Si (CH2259) (mJ/cm2) 1.06 1014cm-2 6.36 1014cm-2 9.80 1014cm-2
0.7 D (cm2/s) 16 (± 0.1) 15.7 (± 0.1) 17.2 (± 0.1)
τR (ns) > 30 >30 20 (± 2)
5.0 D (cm2/s) 13.6 (± 0.1) 13.1 (± 0.1) 12.5 (± 0.3)
τR (ns) > 30 > 30 5.7 (± 0.3)
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Workshop on Defect Analysis in Radiation Damaged Silicon Detectors, Hamburg, 23./24. August 2006 J. Vaitkus
Photo-Hall effect• An influence of impurities on free
carrier mobility.• The indications of scattering on
impurities, clusters and etc.:– According the scattering
coefficient value– According the different
dependence on temperature
I
t
Digital processing:High input impedance, small capacitance !
BMagnetic field up to 2 T
Intense laser pulse
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Workshop on Defect Analysis in Radiation Damaged Silicon Detectors, Hamburg, 23./24. August 2006 J. Vaitkus
( ) x
iiii
iiiii
H BEttne
tAtnetE
∑∑ −
=)()(
)()()1( 2
µ
µ
( ) ( )[ ] wEBrBtEEwtU HHHH ⋅∆=−=∆ µ0
1. Basic relationships:
(3)(5)
(6)
(1)
(2)
(4)
Transient Photo-Hall and photo-magnetoresistance effects
2
2
><><
=ττ m
Hr
2)()( BTt MB
B µρρ
=∆
4
223
><><−>><<
=m
mmmMT
ττττ
eff
m
me ><
=τµ
( ) ( ) ( )tNtvStH
βµµ
+=0
11∑ ><>=<
i imm ττ11
Matthiessen’s rule
(7) (8)
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Workshop on Defect Analysis in Radiation Damaged Silicon Detectors, Hamburg, 23./24. August 2006 J. Vaitkus
Transient Photo-Hall and photo-magnetoresistance effects
2. Practical considerations:
( ) ( ) ( )tNtvStH
βµµ
+=0
11
( ) ( )
10
0000 1111
−
⎟⎟⎠
⎞⎜⎜⎝
⎛∆±
+=⎟⎟⎠
⎞⎜⎜⎝
⎛−∆=−=∆
H
H
H UU
vUwBE
tvSNNSSN
βµµβ ( )1
01−
⎟⎟⎠
⎞⎜⎜⎝
⎛∆
+=H
H
UUtY
( ) ( )[ ] ( )tYconsttNtS ⋅=∆ (12)
(9)(10) (11)
(8)
Further analyze depends on the model and a number of re-chargeable centers
23
.. ~ Tiionµ
( ) 12/1*2−
⎥⎦⎤
⎢⎣⎡= SkTmNe ss
µ
1. ~ −Tbarrµ
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Workshop on Defect Analysis in Radiation Damaged Silicon Detectors, Hamburg, 23./24. August 2006 J. Vaitkus
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Workshop on Defect Analysis in Radiation Damaged Silicon Detectors, Hamburg, 23./24. August 2006 J. Vaitkus
Photo-Hall effect
• If the sample has micro/nano non-uniformities, then the signal is more complex dependent on parameters.
(That should be in a case of change of conductivity type)
• It changes an effective active volume therefore changes the effective Hall-mobility (a lot of models, quite complicated expressions)
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Workshop on Defect Analysis in Radiation Damaged Silicon Detectors, Hamburg, 23./24. August 2006 J. Vaitkus
Photo-ionization spectrumMeasurement of photoconductivity (possible effect also: quenching of
photoconductivity, if additional excitation is used), photo-voltage, short circuit current.
Possible regime of constant signal: varying of excitation. It excludes different non-linearities.
Determination of defect optical ionization energy.
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Workshop on Defect Analysis in Radiation Damaged Silicon Detectors, Hamburg, 23./24. August 2006 J. Vaitkus
Si photoconductivity spectrumSample from Hamburg:
Example of data from literature:
0,8 1,0 1,2 1,4 1,6 1,810-9
10-8
10-7
10-6
I (A
)
ε (eV)
Si CH22374,25e+14pT=79K
2006.06.24
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Workshop on Defect Analysis in Radiation Damaged Silicon Detectors, Hamburg, 23./24. August 2006 J. Vaitkus
Conclusions:
1. It exists additional (time consuming)methods for carrier capture processes and defect parameters measurement.2. It is most important to have the samples, that are interesting for supplier.
Thank You for Your attention!