“Non-traditional methods of material properties and defect ...€¦ · Workshop on Defect...

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


Outline:• Definition of aims• Photoconductivity kinetics• Free carrier diffusion and capture process

measurement • Photo-Hall and magnetoresistance• Photo-ionization spectroscopy


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.


Free carrier kinetics


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!


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)


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.


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.


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


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


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


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)


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



Delay time (ps)

Diff

ract

ion

effic

ienc

y. (a

. u.)

Delay time (ps)


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




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










Rτ

Grating period Λ = 5 µm (diffusion influence).


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)


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


( ) 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)


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


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)


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.


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


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!

“Non-traditional methods of material properties and defect ...€¦ · Workshop on Defect...

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