Photoresponse spectrum in differently irradiated and annealed S i

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


Outline:

• Photoconductivity spectra in differently irradiated and annealed (according the WODEAN

plan) samples

• Model of photoconductivity (the cluster properties included)


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


Non-annealed PCMost surprising: non-monotonous change the contribution of different deep levels: it is an evidence of the random processes in defect generation


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


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


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)


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

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

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


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 @ 1800C


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 @ 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 @ 1800C


15 h @ 1800C

W337-Q6

1e16 cm-2

18 K50 V

Annealing increase the lifetimeAnnealing caused the complicate influence on deep level concentration


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.


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:


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)


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.


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:


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


Thanks for Your attention !


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.


Other series samples

Photoresponse spectrum in differently irradiated and annealed S i

Documents

Transcript of Photoresponse spectrum in differently irradiated and annealed S i