Complex characterization of defect centres in neutron irradiated MCz silicon by PITS, photoluminescence and EPR methods Institute of Electronic Materials

Complex characterization of defect centres in neutron irradiated MCz silicon by PITS, photoluminescence and EPR methods

Institute of Electronic Materials Technology

Joint Laboratory for Characterisation of Defect Centres in Semi-Insulating Materials

Paweł Kamiński, Roman Kozłowski, Jarosław Żelazko, Barbara Surma, and Mariusz Pawłowski

Workshop on Defect Analysis in Radiation-Damaged Silicon Detectors, Vilnius, 2-3 June 2007

Institute of Electronic Materials Technology, 133 Wólczyńska Str. 01-919 Warszawa, Poland

Outline

Samples

HRPITS images of spectral fringes for radiation defects in neutron MCz silicon – effect on the neutron fluence on the defect structure of as-irradiated material

Photoluminescence spectra

Results of EPR measurements

Conclusions

Samples

Starting material:

Okmetic MCz <100> silicon wafers, n-type, 1 kcm, 300 m thick

[O] = 5.5x1017 cm-3

[C] = 2.5x1016 cm-3

Neutron irradiation:

TRIGA reactor in Ljubljana, 1-MeV, fluences: 1x1012, 1x1013, 1x1014, 3x1014, 1x1015, 3x1015, 1x1016, and 3x1016 cm-2

Effect on neutron fluence on the material resistivity

HRPITS images (1)

MCz Si <100> Sample 8556-14-5

Temperature [K]

log(

e T [

s-1])

Am

plit

ude

[a.u

.] T1_1E12

VO

1-MeV neutron fluence 1x1012 cm-2

Laser: 650 nm, 5mW; UA= 3V;Gain: 1x106 V/A; Line width [samples]: 50000; Time Resolution [us]: 10Period [ms]: 505; Average: 150; Illumination pulse width: 50 ms

Trap labelEa

[meV]A

[s-1K-2]e1

[s-1]

Ampe1

[a.u]

e2

[s-1]

Ampe2

[a.u]Identification

T1_1E12 233 (2-3)x104 1x103 0.22 3.2x104 0.40 V22-/-

Two broad spectral fringes obtained by two-dimensional correlation procedure applied to analysis of the photocurrent relaxation waveforms. The left-hand side fringe is due to a number of closely spaced shallow levels with similar concentrations. The right-hand side fringe results from thermal emission of charge carriers from two or three levels including the dominant center T1_1E12.

VO - Ea= 0.17 eV; A= 9.6x106 s-1K-2

HRPITS images (2)

MCz Si <100> Sample 8556-14-6

Temperature [K]

log(

e T [

s-1])

Am

plit

ude

[a.u

.]

T1_1E13

T2_1E13

T3_1E13

T4_1E13

T5_1E13

VO


Trap label Ea[meV] A [s-1K-2] e1 [s-1] Ampe1[a.u] E2 [s

-1] Ampe2[a.u] Identification

T1_1E13 25±2 (2-5)x102 1x103 0.048 3.2x104 0.41 shallow donor


T3_1E13 115±5 (8-20)x105 1x103 0.12 3.2x104 0.46 CiCs(B)-/0 or self-interstitials related

T4_1E13 315±10 (2-4)x106 1x103 0.018 3.2x104 0.091 V22-/- + CiOi

0/+

T5_1E13 470±20 (1-5)x107 1x103 0.024 3.2x104 0.11 V2-/0 + X -/0

Five well separated spectral fringes due to the thermal emission from shallow defect centers T1_1E13, T2_1E13, and T3_1E13, as well as from deep defect centers T4_1E13 and T5_1E13. The shallow levels are predominant.

HRPITS images (3)1-MeV neutron fluence 1x1014 cm-2

MCz Si <100> Sample 8556-14-7

Temperature [K] lo

g(e T

[s-1

])

Am

plit

ude

[a.u

.]

T1_1E14

T2_1E14

T3_1E14

T4_1E14

T5_1E14

VO

Trap label Ea[meV] A[s-1K-2] e1[s-1] Ampe1[a.u] e2[s

-1] Ampe2[a.u] Identification


T2_1E14 60±5 (9-20)x104 1x104 0.022 3.2x104 0.053 CiCs(B)+/0 or self-interstitials related

T3_1E14 103±5 (2-5)x103 1x103 0.04 3.2x104 0.37 CiCs(B)-/0 or self-interstitials related

T4_1E14 324±10 (1-5)x106 3.2x103 0.033 3.2x104 0.125 V22-/- + CiOi

0/+

T5_1E14 505±20 (8-30)x107 1x103 0.049 3.2x104 0.249 V2-/0 + X -/0

Five well separated spectral fringes due to the thermal emission from shallow defect centers T1_1E13, T2_1E13, and T3_1E13, as well as from deep defect centers T4_1E13 and T5_1E13. The concentrations of shallow and deep levels are of the same order of magnitude.


MCz Si <100> Sample 8556-14-8

Temperature [K]

log(

e T [

s-1])

Am

plit

ude

[a.u

.]

T1_3E14

T2_3E14 T3_3E14

T4_3E14

T5_3E14

VO

Trap label Ea [meV] A [s-1K-2] e1 [s-1] Ampe1 [a.u] e2 [s

-1] Ampe2 [a.u] Identification



T3_3E14 240±7 (1-4)x107 1x103 0.06 3.2x104 0.23 V22-/-

T4_3E14 333±10 (2-6)x106 1x103 0.09 3.2x104 0.25 CiOi 0/+

T5_3E14 490±20 (6-9)x107 1x103 0.044 3.2x104 0.25 V2-/0 + X -/0


Trap label Ea [meV] A [s-1K-2] e1 [s-1] Ampe1 [a.u] e2 [s




T3_1E15 74±5 (2-4)x104 1x103 0.008 3.2x104 0.109 self-interstitials related

T4_1E15 325±10 (1-5)x107 3.2x103 0.011 3.2x104 0.042 V22-/- + CiOi

0/+

T5_1E15 420±20 (1-3)x107 1x103 0.047 3.2x104 0.218 V2-/0

MCz Si <100> Sample 8556-14-9

Temperature [K]

log(

e T [

s-1])

Am

plit

ude

[a.u

.]

T2_1E15

T1_1E15

T3_1E15

T4_1E15 T5_1E15

VO

HRPITS images (6)


Trap label Ea [meV] A [s-1K-2] e1 [s-1]

Ampe1

[a.u]e2 [s



T2_3E15 325±10 (1-5)x106 3.2x103 0.08 3.2x104 0.207 V22-/- + CiOi

0/+

T3_3E15 500±20 (3-8)x107 1x103 0.083 3.2x104 0.247 V2-/0 + X -/0

MCz Si <100> Sample 8556-14-10

Am

plit

ude

[a.u

.]

T2_3E15

T1_3E15

T3_3E15

Temperature [K]

log(

e T [

s-1])

VO


Trap labelEa

[meV]A

[s-1K-2]e1

[s-1]

Ampe1

[a.u]

e2

[s-1]

Ampe2

[a.u]Identification


T2_1E16 325±10 (1-5)x107 1x103 0.039 3.2x104 0.141 V22-/- + CiOi

0/+

T3_1E16 455±15 (1-5)x107 1x103 0.114 3.2x104 0.424 V2-/0 + X -/0

MCz Si <100> Sample 8556-14-11

Am

plit

ude

[a.u

.] T2_1E16

T1_1E16

T3_1E16

Temperature [K]

log(

e T [

s-1])

VO


Trap labelEa

[meV]A

[s-1K-2]e1

[s-1]

Ampe1

[a.u]

e2

[s-1]

Ampe2

[a.u]Identification


T2_3E16 320±10 (1-5)x106 1x103 0.11 3.2x104 0.22 V22-/- + CiOi

0/+

T3_3E16 420±15 (5-9)x106 1x103 0.18 3.2x104 0.446 V2-/0 + X -/0

MCz Si <100> Sample 8556-14-12

Am

plit

ude

[a.u

.] T2_3E16

T1_3E16

T3_3E16

Temperature [K]

log(

e T [

s-1])

VO

Effect of neutron fluence on the concentration midgap centres and Fermi level position

Effect of fluence on the concentration of midgap centres

Effect of fluence on the Fermi level position determined from temperature dependence of dark current (TDDC)

Photoluminescence spectra (1)

1.2 1.1 1.0 0.9 0.8 0.7

1.13

8

1.03

7

T=4K

exc. 50W/cm2

488nm Ar*

boun

d ex

cito

ns(T

O)

EH

D

37_E12 #4766 non irradiated

Energy (eV)

PL

(arb

itrar

y un

its)

Si n-irrad

Comparison of photoluminescence spectra taken at the same excitation intensity for a non-irradiated sample (CERN#4766, resistivity 380 Ohmcm) and a MCz-Si sample irradiated with neutrons with a fluence of 1x1012 cm-2 (sample 8556-14-37).

Comparison of photoluminescence spectra for MCz Si samples irradiated with neutron fluences of 1x1012, 1x1013 and 1x1014 cm-2. The decrease in the radiative recombination efficiency with increasing the fluence is seen.

The PL measurements were done using Ar+ laser operated at 488 nm focused to a spot of about 400 micrometers. The luminescence at 4.0-4.3 K was detected using lock-in technique and Hamamatsu photomultiplier type R5509-72 with InGaAsP cathode. The spatial resolution was 1.5 nm for 1 m. The samples were placed on a cool finger and cooled down by using the closed-cycle cooling system.

1.2 1.1 1.0 0.9 0.8 0.7

0.78

9

bound e

xcito

ns(

TO

)

1.13

8

37_E12 38-E13 47_E14

Energy (eV)

PL

(a

rbitr

ary

un

its)

Si n-irradresistivity 2 kcm

T=4K

exc. 50W/cm2

488nm Ar+

1.03

7

CiO

i

line C

Photoluminescence spectra (2)

Comparison of the photoluminescence spectra for a sample of MCz Si irradiated with the neutron fluence of 1x1012 cm-2 and a sample of FZ Si irradiated with the fluence of 5x1016cm-2. The significant differences in the defect structure of the materials are seen.

1.2 1.1 1.0 0.9 0.8 0.7

0.84 0.82 0.80 0.78 0.76

0.7

75

0.7

94

0.7

98

Energy (eV)

(TA

rep

lica

s)

1.15

Si MCZ:O E12n/cm2

resistivity 2000ohmcm

boun

d ex

cito

ns(T

O)

1.13

8

Energy (eV)

PL

(a

rbitr

ary

un

its)

T=4K

exc. 50W/cm2

488nm Ar+

1.03

7

P(N

FL

)

C

1.2 1.1 1.0 0.9 0.8

Si FZ:O 5*e16n/cm2

resistivity 800ohmcmas irradiated

Energy (eV)

PL

(a

rbitr

ary

un

its)

T=6K

exc. 50W/cm2

488nm Ar+

W

C

Results of EPR measurementsThe EPR spectra were measure using Bruker ESP-300 X-band (~9.4 GHz) spectrometer with 100 kHz magnetic field modulation and phase sensitive detection. A helium gas-flow Oxford Instruments cryostat was used for measurments in the temperature range 6–200 K.

EPR spectra measured at T=6 K for MCZ Si irradiated with various fluence of 1-MeV neutrons.

Red line – reference sample. One defect with axis symmetry along <100> directions and with S=1/2. To establish the microscopic structure of the defect, further investigations are needed. Green line – sample irradiated with the fluence of 1x1015 cm-2. Two weak broad lines of unknown origin. Change of the defect structure compared to the reference sample. Blue line - sample irradiated with the fluence of 3x1015 cm-2. The isotropic line (g=2.40) is observed similarly as in the sample irradiated with the lower fluence. The new anisotropic line (g=1.90) is seen.

50 100 150 200 250 300 350

-6

-4

-2

0

2

4

6

g=10,42

defect relatedanisotropic line

Am

plit

ud

e E

PR

[a

rb.u

.]

B [mT]

reference sample

CZ6-3 1e15 cm-2

CZ6-6 3e15 cm-2

g=12,9

g=4,757g=2,40

g=2,0056surface defect

defect relatedanisotropic line

marker

(Al2O

3:Cr3+)

T = 6 KB II <100>

Conclusions (1)

High-resolution photoinduced transient spectroscopy (HRPITS), photoluminescence (PL) and electron paramagnetic resonance (EPR) measurements have been used to studying the effect of neutron fluence on defect structure of as-irradiated MCz-Si. In the HRPITS method, a new approach involving imaging the temperature changes of the amplitudes and time constants of the photocurrent relaxation waveforms resulting from the thermal emission of charge carriers from defect centres has been implemented. The midgap centres V2

-/0 + X -/0, controlling the Fermi level position in the as-irradiated material have been found to arise at the neutron fluence of 1x1013 cm-2. The concentration of the centres generated by this fluence is, however, five times lower than that of the shallow defect centres with the activation energy of 115 meV. For the neutron fluence of 1x1014 cm-2, the concentration of the midgap centres V2

-/0 + X -/0 becomes approximately equal to the concentration of shallow centres with the activation energy of 103 meV. The increase of the fluence to 3x1014 cm-2 results in substantial increasing (threefold) the concentration of defects related to carbon interstitials: the shallow traps with activation energy of 62 meV (CiCs(B)+/0) and the traps with activation energy of 330 meV (CiOi

0/+).

Conclusions (2)

For the neutron fluences ranging from 3x1015 to 3x1016 cm-2, the concentration of the midgap centres V2

-/0 + X -/0 significantly increases. On the other hand, the concentration of the shallow defect centres decreases. The activation energy of the shallow defects also decreases from 43 meV to 31 meV. The PL spectra indicate that the non-radiative recombination rate strongly increases with increasing the fluence from 1x1012 to 1x1014 cm-2. A line at 1.037 eV, related to point defects produced by neutron irradiation, has been observed for low fluences 1x1012 and 1x1013 cm-2. The results of EPR measurements show the changes in the material defect structure resulting from the neutron irradiation. However, establishing the atomic configurations of the detected defects requires further investigations.

Acknowledgement

The authors want to thank Prof. Gunnar Lindstroem for his effort put into the coordination of research within the framework of the WODEAN project.

We would like also to thank Gregor Kramberger for performing the neutron irradiations.

This work was carried out within the framework of the RD 50 project with financial support of the Polish Ministry of Science and Higher Education under grant No. CERN/15/2007.

Documents

Complex characterization of defect centres in neutron irradiated MCz silicon by PITS, photoluminescence and EPR methods Institute of Electronic Materials