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Photoresponse spectrum in differently irradiated and annealed S i. Juozas Vaitkus Vilnius University, Lithuania On behalf of PC spectra group: V.Kalendra, V.Kazukauskas and N.Vainorius, and the lifetime group: E.Gaubas. Outline:. - PowerPoint PPT Presentation
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J.Vaitkus. WODEAN Workshop,13-15 May, 2010, Bucurest
Photoresponse spectrum in differently irradiated and
annealed Si
Juozas Vaitkus
Vilnius University, LithuaniaOn behalf of PC spectra group: V.Kalendra, V.Kazukauskas and N.Vainorius,
and the lifetime group: E.Gaubas
J.Vaitkus. WODEAN Workshop,13-15 May, 2010, Bucurest
Outline:
• Photoconductivity spectra in differently irradiated and annealed (according the WODEAN
plan) samples
• Model of photoconductivity (the cluster properties included)
J.Vaitkus. WODEAN Workshop,13-15 May, 2010, Bucurest
Photoconductivity spectrum gives information:
• Constant excitation:– Intrinsic region – the signal related to the free carrier
lifetime, i.e. recombination efficiency.– Extrinsic region – the signal gives information about
the deep levels• Pulse excitation (40 fs) (microwave measurement)
– Photo-ionization rate– Recombination (capture) time constant
J.Vaitkus. WODEAN Workshop,13-15 May, 2010, Bucurest
Non-annealed PCMost surprising: non-monotonous change the contribution of different deep levels: it is an evidence of the random processes in defect generation
J.Vaitkus. WODEAN Workshop,13-15 May, 2010, Bucurest
1e13 cm-2
0,6 0,8 1,0 1,210-1
100
101
102
103
104
105
106
initial
tretaed @ 80o 4min
treated @ 80o 15val
itreated @ 120oC 15val
1E13
abs
I (pA
)
h, eV
T=18KU= -50V
1,10 1,15 1,20 1,25 1,30
0,2
0,4
0,6
0,8
1,0
initial
tretaed @ 80o 4min
treated @ 80o 15val
itreated @ 120oC 15val
1E13
abs
I (A
)
h, eV
T=18KU= -50V
0,75 0,80 0,85 0,90 0,95 1,00 1,05 1,10 1,15
200
400
initial
tretaed @ 80o 4min
treated @ 80o 15val
itreated @ 120oC 15val
1E13
abs
I (p
A)
h, eV
T=18KU= -50V
1) Annealing influences the lifetime (at the beginning the increase, later – decrease)
2) Annealing decrease the level at the valence band concentration (Eopt~0.9 eV)
J.Vaitkus. WODEAN Workshop,13-15 May, 2010, Bucurest
1e14 cm-2
0,5 0,6 0,7 0,8 0,9 1,0 1,1 1,2 1,3 1,41E-13
1E-12
1E-11
1E-10
1E-9
1E-8
1E-7
1E-6
1E-5
1E-4
W3371e14
I. re
l.u.
, nm
non-treated
4 min @ 800C
15 h @ 800C
15 h @ 1200C smoothing
15 h @ 1200C
15 h @ 1800C
1,1 1,2 1,30
5
10
15
20
25
30
W3371e14
I, A
, nm
non-treated
4 min @ 800C
15 h @ 800C
15 h @ 1200C smoothing
15 h @ 1200C
15 h @ 1800C
0,7 0,8 0,9 1,0 1,10
20
40
W3371e14
I, nA
.
, nm
non-treated
4 min @ 800C
15 h @ 800C
15 h @ 1200C smoothing
15 h @ 1200C
15 h @ 1800C
1) Annealing influences the lifetime (at the beginning the increase, later – decrease)
2) Annealing decrease the the level at the valence band concentration (Eopt~0.9 eV), but at higher T – the defect system reconstruction
J.Vaitkus. WODEAN Workshop,13-15 May, 2010, Bucurest
1e16 cm-2
0,5 0,6 0,7 0,8 0,9 1,0 1,1 1,2 1,310-13
10-12
10-11
10-10
10-9
10-8
10-7
10-6
10-5
I, re
l.u.
h, eV
non-treated
4 min @ 800C
15 h @ 800C
15 h @ 1200C smoothing
15 h @ 1800C
15 h @ 1200C smoothing
15 h @ 1800C
W337-Q6
1e16 cm-2
18 K50 V
0,7 0,8 0,9 1,0 1,1 1,20,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8
2,0
I, A
.
h, eV
non-treated
4 min @ 800C
15 h @ 800C
15 h @ 1200C smoothing
15 h @ 1800C smoothing
15 h @ 1800C
W337-Q6
1e16 cm-2
18 K50 V
1,0 1,1 1,2 1,3
0,5
1,0
1,5
2,0
2,5
I, r
el.u
.
h, eV
non-treated
4 min @ 800C
15 h @ 800C
15 h @ 1200C smoothing
15 h @ 1800C
15 h @ 1200C smoothing
15 h @ 1800C
W337-Q6
1e16 cm-2
18 K50 V
Annealing increase the lifetimeAnnealing caused the complicate influence on deep level concentration
J.Vaitkus. WODEAN Workshop,13-15 May, 2010, Bucurest
40 fs pulse excitation, RTThe difference of dc 18 K and pulse @ RT: more shallow levels are observed
the quenching is more significant.Annealing reduced quenching by 0.41 eV and the contribution of most deep levels (probably disorder origin), but enhanced level at 0.82 eV.
J.Vaitkus. WODEAN Workshop,13-15 May, 2010, Bucurest
1) the kick off by neutron Si atom creates the vacancy-interstitials cluster (Huhtinen – track consisting vacancies and Si disorder).2) the generation-recombination induced phonons and low temperature annealing leads to the cluster reconstruction to the different vacancy clusters and the gettering of other defects.
J.L. Hastings, S.K. Estreicher, P.A. Fedders. Vacancy aggregates in silicon. Phys. Rev. B, Vol. 56 (16), p. 10215-10220 (1997).
J. Dong, D. A. Drabold. Atomistic Structure of Band-Tail States in a-Si. Phys. Rev. Lett. Vol. 80 (9) p. 1928-1931 (1998). The valence tail is primarily due to structural disorder, while the conduction tail is much more sensitive to temperature and originates in thermal disorder.
All results can be understood by the cluster transform model:
J.Vaitkus. WODEAN Workshop,13-15 May, 2010, Bucurest
Simulation review:
Initial distribution of vacancies produced by 1 MeV neutron in Si, a – a result of kick of Si atom, and b – if a fluence was 1014 cm-2, according M.Huhtinen. NIMA 491 (2002) 194–215
0.05 m
G.Davies, presentation at the WODEAN workshop in Bucharest: reconstructions inside 100 nm size volume (all inside the Debye sphere)
J.Vaitkus. WODEAN Workshop,13-15 May, 2010, Bucurest
Photo-ionization of the clusterDifferent deep levels onside the volume surrounded by a single potential barrier.
E
x
Annealing change the compensation in the bulk, i.e., barrier, and the structure (i.e., properties) of deep levels inside the cluster.
J.Vaitkus. WODEAN Workshop,13-15 May, 2010, Bucurest
The talk of Gordon Davies in Bucharest demonstrated that the main transforms during self-annealing and different treatment are going inside the
cluster where different random processes happens.
Our results show that by photoconductivity a the changes in the deep level system can be controlled.
The positive and negative contribution on the photoconductivity allow to recognize the levels that influence the carrier capture by the cluster.
Conclusion 1:
J.Vaitkus. WODEAN Workshop,13-15 May, 2010, Bucurest
Conclusion 2:
Irradiation and low T annealing effect demonstrate:• Extrinsic photoconductivity reveals a few deep
levels that are directly related to the irradiation.• Low T annealing allows to propose the random
transforms in the defect system
J.Vaitkus. WODEAN Workshop,13-15 May, 2010, Bucurest
Thanks for Your attention !
J.Vaitkus. WODEAN Workshop,13-15 May, 2010, Bucurest
The comparison of the acting quantities confirming the model
1) Fermi level location determined from the free carrier concentration (proposing the existence of the conductivity channels, the error related to the indefinite of the volume participating in the percolation)
2) Local level energy is determined from the temperature dependence of the free carrier concentration.
3) The Debye radius is evaluated neglecting the ionized defects between the clusters. (If it would be included, the overlap would be less)
4) The cluster separation distance evaluated using the approximation of linear dependence of the cluster concentration on the fluence.
J.Vaitkus. WODEAN Workshop,13-15 May, 2010, Bucurest
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