Magnetic field-stimulated change of photovoltage in solar silicon crystals
The effect of static magnetic field (B = 0.17 T) on composition of defects and lifetime of charge carriers in solar silicon crystals has been investigated. Studied in this work was the character of changes in electrical characteristic of solar silicon. These changes are dependent on the time elap...
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| Cite this: | Magnetic field-stimulated change of photovoltage in solar silicon crystals / O.O. Korotchenkov, L.P. Steblenko, A.O. Podolyan, D.V. Kalinichenko, P.O. Tesel’ko, V.M. Kravchenko, N.V. Tkach // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2013. — Т. 16, № 1. — С. 72-75. — Бібліогр.: 10 назв. — англ. |
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Korotchenkov, O.O. Steblenko, L.P. Podolyan, A.O. Kalinichenko, D.V. Tesel’ko, P.O. Kravchenko, V.M. Tkach, N.V. 2017-05-26T06:03:50Z 2017-05-26T06:03:50Z 2013 Magnetic field-stimulated change of photovoltage in solar silicon crystals / O.O. Korotchenkov, L.P. Steblenko, A.O. Podolyan, D.V. Kalinichenko, P.O. Tesel’ko, V.M. Kravchenko, N.V. Tkach // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2013. — Т. 16, № 1. — С. 72-75. — Бібліогр.: 10 назв. — англ. 1560-8034 PACS 61.72.-y, 68.43.-h, 72.40.+w, 76.60.-k, 81.40.Rs https://nasplib.isofts.kiev.ua/handle/123456789/117665 The effect of static magnetic field (B = 0.17 T) on composition of defects and lifetime of charge carriers in solar silicon crystals has been investigated. Studied in this work was the character of changes in electrical characteristic of solar silicon. These changes are dependent on the time elapsed after the magnetic treatment. The results have been discussed in terms of spin-dependent processes in the subsystem of structural defects. en Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України Semiconductor Physics Quantum Electronics & Optoelectronics Magnetic field-stimulated change of photovoltage in solar silicon crystals Article published earlier |
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Magnetic field-stimulated change of photovoltage in solar silicon crystals |
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Magnetic field-stimulated change of photovoltage in solar silicon crystals Korotchenkov, O.O. Steblenko, L.P. Podolyan, A.O. Kalinichenko, D.V. Tesel’ko, P.O. Kravchenko, V.M. Tkach, N.V. |
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Magnetic field-stimulated change of photovoltage in solar silicon crystals |
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Magnetic field-stimulated change of photovoltage in solar silicon crystals |
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Magnetic field-stimulated change of photovoltage in solar silicon crystals |
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Magnetic field-stimulated change of photovoltage in solar silicon crystals |
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magnetic field-stimulated change of photovoltage in solar silicon crystals |
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Korotchenkov, O.O. Steblenko, L.P. Podolyan, A.O. Kalinichenko, D.V. Tesel’ko, P.O. Kravchenko, V.M. Tkach, N.V. |
| author_facet |
Korotchenkov, O.O. Steblenko, L.P. Podolyan, A.O. Kalinichenko, D.V. Tesel’ko, P.O. Kravchenko, V.M. Tkach, N.V. |
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2013 |
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English |
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Semiconductor Physics Quantum Electronics & Optoelectronics |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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Article |
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The effect of static magnetic field (B = 0.17 T) on composition of defects and
lifetime of charge carriers in solar silicon crystals has been investigated. Studied in this
work was the character of changes in electrical characteristic of solar silicon. These
changes are dependent on the time elapsed after the magnetic treatment. The results have
been discussed in terms of spin-dependent processes in the subsystem of structural
defects.
|
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1560-8034 |
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https://nasplib.isofts.kiev.ua/handle/123456789/117665 |
| citation_txt |
Magnetic field-stimulated change of photovoltage in solar silicon crystals / O.O. Korotchenkov, L.P. Steblenko, A.O. Podolyan, D.V. Kalinichenko, P.O. Tesel’ko, V.M. Kravchenko, N.V. Tkach // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2013. — Т. 16, № 1. — С. 72-75. — Бібліогр.: 10 назв. — англ. |
| work_keys_str_mv |
AT korotchenkovoo magneticfieldstimulatedchangeofphotovoltageinsolarsiliconcrystals AT steblenkolp magneticfieldstimulatedchangeofphotovoltageinsolarsiliconcrystals AT podolyanao magneticfieldstimulatedchangeofphotovoltageinsolarsiliconcrystals AT kalinichenkodv magneticfieldstimulatedchangeofphotovoltageinsolarsiliconcrystals AT teselkopo magneticfieldstimulatedchangeofphotovoltageinsolarsiliconcrystals AT kravchenkovm magneticfieldstimulatedchangeofphotovoltageinsolarsiliconcrystals AT tkachnv magneticfieldstimulatedchangeofphotovoltageinsolarsiliconcrystals |
| first_indexed |
2025-11-25T23:46:37Z |
| last_indexed |
2025-11-25T23:46:37Z |
| _version_ |
1850583664683909120 |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2013. V. 16, N 1. P. 72-75.
© 2013, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
72
PACS 61.72.-y, 68.43.-h, 72.40.+w, 76.60.-k, 81.40.Rs
Magnetic field-stimulated change of photovoltage
in solar silicon crystals
O.O. Korotchenkov, L.P. Steblenko, A.O. Podolyan, D.V. Kalinichenko, P.O. Tesel’ko,
V.M. Kravchenko, N.V. Tkach
Taras Shevchenko Kyiv National University, Physics Department,
4, prosp. Akademika Glushkova, Kyiv, Ukraine
Abstract. The effect of static magnetic field (B = 0.17 T) on composition of defects and
lifetime of charge carriers in solar silicon crystals has been investigated. Studied in this
work was the character of changes in electrical characteristic of solar silicon. These
changes are dependent on the time elapsed after the magnetic treatment. The results have
been discussed in terms of spin-dependent processes in the subsystem of structural
defects.
Keywords: magnetic field, solar silicon crystal, surface photovoltage, structure
relaxation, charged defects, adsorption.
Manuscript received 28.08.12; revised version received 19.11.12; accepted for
publication 26.01.13; published online 28.02.13.
1. Introduction
In recent years, weak magnetic field-stimulated
magnetosensitive phenomena in weak-magnetic crystals
are of increased interest. This kind of physical
phenomena is taken into account by the models
involving spin-dependent intercombination transitions in
pairs of non-equilibrium paramagnetic defects [1-4]. The
probability of decay of a structural complex containing
at least two radicals each of which has a spin angular
momentum depending on mutual orientation of the
spins. Magnetic field (MF) is believed to have an
influence on the probability of initiation of favourable
orientation and stimulates singlet-triplet transitions. Spin
conversion, in turn, shifts the chemical solid-state
reaction towards decay.
By now, a large amount of experimental data has
been accumulated, and a number of interesting effects
has been detected [5, 6] in systematic investigations of
the effect of weak magnetic fields (B ≤ 1 T) on
magnetically disorded (weak-magnetic) materials.
Taking into account the fact that silicon is the basic
structural material of microelectronics, the portion of
the mentioned studies on silicon crystals is
unwarrantably small.
Especially noticeable gaps exist in the knowledge
of magnetostimulated changes in the electrophysical
characteristics of silicon. The respective studies have not
been carried out on solar silicon (SS) crystals at all.
Meanwhile, that kind of studies is urgent and
worthwhile, since microelectronic devices, manufactured
on the SS basis, most often operate under extreme
conditions, including the action of magnetic fields.
Therefore, the operation of SS-based devices must be
predictable and reliable.
It should be noted that investigation of
electrophysical characteristics of SS such as
photovoltage makes it possible to obtain important
information on the electron subsystem of SS crystals.
That kind of studies also provide particular information
on interaction of charge carriers (photocarriers)
generated by absorption of electromagnetic radiation
(photons) with inhomogeneities caused by structural
peculiarities in SS crystals.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2013. V. 16, N 1. P. 72-75.
© 2013, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
73
A lack of studies concerning the action of magnetic
field on photovoltage in SS crystals and practical
necessity of such investigations make the present work
quite appropriate. The aim was to reveal changes in the
photovoltage magnitude and decay behaviour caused by
the action of a weak constant magnetic field.
2. Experimental
Boron-doped Czochralski-grown solar Si crystals with
the resistivity = 5 Ohmcm were studied. Magnetic
treatment (MT) of SS samples consisted in exposing
them to constant magnetic field with an induction of
B = 0.17 T during certain period of time lasting from
tMT = 5 to 30 days. Photovoltage measurements were
carried out by the contactless capacitance method. The
principles of this method are described in [7]. Charge
carriers were generated by light pulses from a LED with
emission spectrum peak at 650 nm and pulse duration of
a few microseconds. All this provided the surface
generation of charge carriers.
3. Results and discussion
The measured photovoltage decay kinetics show two
relaxation components: fast and slow ones (Fig. 1).
Using the method of approximation, we distinguished
fast (τ1) and slow (τ2) components of the charge carrier
lifetime in both the reference SS samples and the
magnetic-field-treated ones.
Fig. 2 illustrates a change in charge carrier lifetime
with duration of MT. One can see that magnetic
treatment for tMT = 5 days results in a decrease in both
fast (τ1) and slow (τ2) lifetime components. Both
components fall approximately 3 times. Further
prolongation of MT duration (tMT = 30 days) does not
affect τ1 and τ2.
10 100 1000
0,00
2,50x10-3
5,00x10-3
7,50x10-3
1,00x10-2
1,25x10-2
1,50x10-2
t, s
U
,
V
1
2
Fig. 1. Photovoltage decay kinetics in SS samples: the
reference sample (1) and the sample exposed to magnetic field
for 21 days (2).
In this work, we studied not only the effect of
lifetime change as a result of MT with varied duration,
which was detected directly after MT, but we also
examined the lifetime constancy. It was found that after
MT termination the slow photovoltage decay time
constant τ2 remains unchanged, while the fast one τ1
decreases slowly with time (Fig. 3). On the whole, the
time constant τ1 fell approximately 5 times for the first
30 days and then remained almost constant for 230 days.
0 4 8 12 16 20 24 28 32
21
28
35
42
49
56
63
70
77
84
91
98
105
s
t
MT
, days
s
s
1
2
100
150
200
250
300
350
400
450
500
550
600
650
700
750
800
s
Fig. 2. Dependence of fast (1) and slow (2) photovoltage decay
time constants on duration of magnetic treatment of SS
samples.
0 25 50 75 100 125 150 175 200 225 250
0
10
20
30
40
80
90
100
110
а)
value just after MT
s
t
MT
, days
value before MT
0 25 50 75 100 125 150 175 200 225 250
150
175
200
225
250
275
300
325
700
750
800
б)
value just after MT
value before MT
s
t
MT
, days
Fig. 3. Fast (a) and slow (b) photovoltage decay time constants
vs time that elapsed after MT termination.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2013. V. 16, N 1. P. 72-75.
© 2013, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
74
Explanation of the results obtained may be based
on the following considerations. A decrease in the time
constant after 5-day-long exposition to magnetic field
can be attributed to magnetic field-stimulated breakage
of chemical bonds in structural nanoclusters, first of all,
the bonds in oxide precipitates (SiOx) and hydride
groups (SiH), which predominate in silicon. Some
saturation observed on the dependence of on tMT
(Fig. 2) may be due to the fact that after 5 days the
process of spin-dependent decay of structural
nanoclusters in silicon had finished and further
prolongation of MT duration had no effect. Point defect
complex decay itself results in appearance of additional
defects in the form of dangling bonds. Among newly
formed defects, there are also electrically active defects
which act as recombination centers. In our opinion, in
addition to electrically active dangling bonds, the defects
of that kind may be defects in the form of non-bridge
oxygen. It is known from literature that in the system
“silicon – silicon oxide” (it is the system that we deal
with in our experiments) the Si-SiO2 interface contains
certain quantity of such defects as non-bridge silicon
(oxygen radicals that is not saturated by silicon) [8].
Non-bridge oxygen is a charged defect [8], it can
act as a recombination center and decrease the charge
carrier lifetime. Moreover, as shown in our previous
work [9], negative electric charge formed on the Si-SiO2
interface under action of magnetic field stimulates the
process of surface gettering the positive ions of alkali
metals K+, Na+, Ca+ and Al+ which are present in Si
bulk. These ions can also act as recombination centers
and decrease the charge carrier lifetime as a result of 5-
day-long MT.
Table 1. Distribution of carbon and oxygen impurities as
well as the host element silicon in the initial SS sample.
Spectrum No. C, wt.% O, wt.% Si, wt.%
1 1.43 0.19 98.57
2 1.79 0.31 98.21
3 1.59 0.33 98.41
4 5.82 0.03 93.72
5 1.65 98.35
Mean 2.45 0.21 97.45
Max. 5.82 0.33 98.57
Min. 1.43 0.03 93.72
Table 2. Distribution of carbon and oxygen impurities as
well as the host element silicon in the SS sample subjected
to MT.
Spectrum No. C, wt.% O, wt.% Si, wt.%
1 10.32 0.50 89.18
2 11.09 0.47 88.44
3 5.00 0.13 94.87
4 4.51 0.21 95.28
Mean 7.73 0.33 91.94
Max. 11.09 0.50 95.28
Min. 4.51 0.13 88.44
Our studies of impurity composition of the SS
samples by using X-ray spectroscopy have shown that
distribution of carbon and oxygen impurities as well as
the host element silicon in the near-surface layers of the
SS crystals is non-uniform (Table 1).
The MT somewhat increases the degree of non-
uniformity in the distribution of the above-mentioned
impurities (Table 2).
As already noted, MT-modified τ2 component
remains constant for a long time (230 days). Taking
into account the fact that barrier-layer photovoltage (it
is the type of photovoltage that we deal with) is
generated in chemically heterogeneous and non-
uniformly doped semiconductors, one can suppose that
the effect of long-lasting invariability of the τ2
component of photovoltage decay in SS after MT may
be due to existence of constant (invariable with time)
structural inhomogeneity in the bulk part of the SS
sample.
At the same time, the effect of long-lasting
decrease in the fast component τ1 after MT may be
attributed to not only structural inhomogeneity in the
bulk part of the SS but also structural inhomogeneity of
the surface. In our opinion, it is the defect and impurity
state of the surface that changes as time interval between
MT termination and measurement of photovoltage decay
kinetics rises. Let us dwell on this point in more detail. It
is known from literature [9, 10] that, in addition to the
process of chemical bond breakage in point defect
complexes, magnetic field also stimulates the processes
of adsorption and gettering the impurities on MT-
activated surface.
An adsorbed particle can be considered as a donor
or acceptor impurity. Adsorbed particles may be charged
or neutral and may exchange charge carriers with the
crystal. So, the process of adsorption can generate new
energy levels at the semiconductor interface. It is not
inconceivable that, under conditions of our experiment
on the MT-activated surface, adsorbed are hydroxyl
groups and oxygen from the ambient atmosphere. These
adsorbed centers, number of which rises with time,
generate additional surface electron states on the Si
surface and, consequently, cause a decrease in the charge
carrier lifetime during some 30 days after MT
termination.
An MT-induced increase in the degree of structural
inhomogeneity in SS led not only to changes in the
electro-physical characteristics (photovoltage decay
kinetics) but also to changes in internal stresses which
result in sample bending, i.e. to alteration of the radius
of curvature of atomic planes. Complementary studies of
sample deformation were carried out by X-ray
diffractometric measurements of the curvature of atomic
planes. It was found that MT decreases the radius of
curvature. The latter may be caused by MT-stimulated
process of structural relaxation, which is the reason of a
decrease in internal microstresses.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2013. V. 16, N 1. P. 72-75.
© 2013, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
75
References
1. Ya.B. Zeldovich, A.L. Buchachenko, E.L.
Frankevich, Magnetic-spin effects in chemistry and
molecular physics // Uspekhi Fiz. Nauk, 155(1),
p. 3-45 (1988), in Russian.
2. M.I. Molotskiy, Possible mechanism of the
magnetoplastic effect // Fizika Tverd. Tela, 33(10),
p. 3112 (1991), in Russian.
3. A.L. Buchachenko, Magnetoplasticity of diamagnetic
crystals in microwave fields // Zhurnal Eksperiment.
Teor. Fiziki, 132(3), p. 673-679 (2007), in Russian.
4. A.L. Buchachenko, Physical kinetics of
magnetoplasticity for diamagnetic crystals //
Zhurnal Eksperiment. Teor. Fiziki, 132(4), p. 827-
830 (2007), in Russian.
5. R.B. Morgunov, Spin micromechanics in the
physics of plasticity // Uspekhi Fiz. Nauk, 174(2),
p. 131-153 (2004), in Russian.
6. Yu.I. Golovin, Magnetoplasticity of solids
(Review) // Fizika Tverd. Tela, 46(5), p. 769-803
(2004), in Russian.
7. L. Kronik and Y. Shapira, Surface photovoltage
techniques: Theory, experiment, and applications //
Surf. Sci. Repts. 37(1-5), p. 1-206 (1999).
8. V.S. Vavilov, V.F. Kiselev, B.N. Mukashev,
Defects in Silicon and on its Surface. Nauka Publ.,
Moscow, 1990 (in Russian).
9. V.A. Makara, M.A. Vasilyev, L.P. Steblenko et al.
Magnetic-field-induced changes in the impurity
state and microhardness of silicon crystals // Fizika
Tekhnika Poluprovodnikov, 42(9), p. 1061-1064
(2008), in Russian.
10. M.N. Levin, A.V. Tatarintsev, O.A. Kostsov, A.M.
Kostsov, Semiconductor surface activation by the
action of pulsed magnetic field // Zhurnal
Tekhnich. Fiziki, 73(10), p. 85-87 (2003), in
Russian.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2013. V. 16, N 1. P. 72-75.
PACS 61.72.-y, 68.43.-h, 72.40.+w, 76.60.-k, 81.40.Rs
Magnetic field-stimulated change of photovoltage
in solar silicon crystals
O.O. Korotchenkov, L.P. Steblenko, A.O. Podolyan, D.V. Kalinichenko, P.O. Tesel’ko,
V.M. Kravchenko, N.V. Tkach
Taras Shevchenko Kyiv National University, Physics Department,
4, prosp. Akademika Glushkova, Kyiv, Ukraine
Abstract. The effect of static magnetic field (B = 0.17 T) on composition of defects and lifetime of charge carriers in solar silicon crystals has been investigated. Studied in this work was the character of changes in electrical characteristic of solar silicon. These changes are dependent on the time elapsed after the magnetic treatment. The results have been discussed in terms of spin-dependent processes in the subsystem of structural defects.
Keywords: magnetic field, solar silicon crystal, surface photovoltage, structure relaxation, charged defects, adsorption.
Manuscript received 28.08.12; revised version received 19.11.12; accepted for publication 26.01.13; published online 28.02.13.
1. Introduction
In recent years, weak magnetic field-stimulated magnetosensitive phenomena in weak-magnetic crystals are of increased interest. This kind of physical phenomena is taken into account by the models involving spin-dependent intercombination transitions in pairs of non-equilibrium paramagnetic defects [1-4]. The probability of decay of a structural complex containing at least two radicals each of which has a spin angular momentum depending on mutual orientation of the spins. Magnetic field (MF) is believed to have an influence on the probability of initiation of favourable orientation and stimulates singlet-triplet transitions. Spin conversion, in turn, shifts the chemical solid-state reaction towards decay.
By now, a large amount of experimental data has been accumulated, and a number of interesting effects has been detected [5, 6] in systematic investigations of the effect of weak magnetic fields (B ≤ 1 T) on magnetically disorded (weak-magnetic) materials. Taking into account the fact that silicon is the basic structural material of microelectronics, the portion of the mentioned studies on silicon crystals is unwarrantably small.
Especially noticeable gaps exist in the knowledge of magnetostimulated changes in the electrophysical characteristics of silicon. The respective studies have not been carried out on solar silicon (SS) crystals at all. Meanwhile, that kind of studies is urgent and worthwhile, since microelectronic devices, manufactured on the SS basis, most often operate under extreme conditions, including the action of magnetic fields. Therefore, the operation of SS-based devices must be predictable and reliable.
It should be noted that investigation of electrophysical characteristics of SS such as photovoltage makes it possible to obtain important information on the electron subsystem of SS crystals. That kind of studies also provide particular information on interaction of charge carriers (photocarriers) generated by absorption of electromagnetic radiation (photons) with inhomogeneities caused by structural peculiarities in SS crystals.
A lack of studies concerning the action of magnetic field on photovoltage in SS crystals and practical necessity of such investigations make the present work quite appropriate. The aim was to reveal changes in the photovoltage magnitude and decay behaviour caused by the action of a weak constant magnetic field.
2. Experimental
Boron-doped Czochralski-grown solar Si crystals with the resistivity ( = 5 Ohm(cm were studied. Magnetic treatment (MT) of SS samples consisted in exposing them to constant magnetic field with an induction of B = 0.17 T during certain period of time lasting from tMT = 5 to 30 days. Photovoltage measurements were carried out by the contactless capacitance method. The principles of this method are described in [7]. Charge carriers were generated by light pulses from a LED with emission spectrum peak at 650 nm and pulse duration of a few microseconds. All this provided the surface generation of charge carriers.
3. Results and discussion
The measured photovoltage decay kinetics show two relaxation components: fast and slow ones (Fig. 1). Using the method of approximation, we distinguished fast (τ1) and slow (τ2) components of the charge carrier lifetime in both the reference SS samples and the magnetic-field-treated ones.
Fig. 2 illustrates a change in charge carrier lifetime with duration of MT. One can see that magnetic treatment for tMT = 5 days results in a decrease in both fast (τ1) and slow (τ2) lifetime components. Both components fall approximately 3 times. Further prolongation of MT duration (tMT = 30 days) does not affect τ1 and τ2.
10
100
1000
0,00
2,50x10
-3
5,00x10
-3
7,50x10
-3
1,00x10
-2
1,25x10
-2
1,50x10
-2
t,
m
s
U, V
1
2
Fig. 1. Photovoltage decay kinetics in SS samples: the reference sample (1) and the sample exposed to magnetic field for 21 days (2).
In this work, we studied not only the effect of lifetime change as a result of MT with varied duration, which was detected directly after MT, but we also examined the lifetime constancy. It was found that after MT termination the slow photovoltage decay time constant τ2 remains unchanged, while the fast one τ1 decreases slowly with time (Fig. 3). On the whole, the time constant τ1 fell approximately 5 times for the first 30 days and then remained almost constant for 230 days.
048121620242832
21
28
35
42
49
56
63
70
77
84
91
98
105
s
t
MT
, days
s
s
1
2
100
150
200
250
300
350
400
450
500
550
600
650
700
750
800
s
Fig. 2. Dependence of fast (1) and slow (2) photovoltage decay time constants on duration of magnetic treatment of SS samples.
0
25
50
75
100
125
150
175
200
225
250
0
10
20
30
40
80
90
100
110
à
)
t
1
value just after MT
t
1
, m
s
t
MT
, days
t
1
value before MT
0
25
50
75
100
125
150
175
200
225
250
150
175
200
225
250
275
300
325
700
750
800
á
)
t
2
value just after MT
t
2
value before MT
t
2
, m
s
t
MT
, days
Fig. 3. Fast (a) and slow (b) photovoltage decay time constants vs time that elapsed after MT termination.
Explanation of the results obtained may be based on the following considerations. A decrease in the time constant after 5-day-long exposition to magnetic field can be attributed to magnetic field-stimulated breakage of chemical bonds in structural nanoclusters, first of all, the bonds in oxide precipitates (SiOx) and hydride groups (SiH), which predominate in silicon. Some saturation observed on the dependence of ( on tMT (Fig. 2) may be due to the fact that after 5 days the process of spin-dependent decay of structural nanoclusters in silicon had finished and further prolongation of MT duration had no effect. Point defect complex decay itself results in appearance of additional defects in the form of dangling bonds. Among newly formed defects, there are also electrically active defects which act as recombination centers. In our opinion, in addition to electrically active dangling bonds, the defects of that kind may be defects in the form of non-bridge oxygen. It is known from literature that in the system “silicon – silicon oxide” (it is the system that we deal with in our experiments) the Si-SiO2 interface contains certain quantity of such defects as non-bridge silicon (oxygen radicals that is not saturated by silicon) [8].
Non-bridge oxygen is a charged defect [8], it can act as a recombination center and decrease the charge carrier lifetime. Moreover, as shown in our previous work [9], negative electric charge formed on the Si-SiO2 interface under action of magnetic field stimulates the process of surface gettering the positive ions of alkali metals K+, Na+, Ca+ and Al+ which are present in Si bulk. These ions can also act as recombination centers and decrease the charge carrier lifetime as a result of 5-day-long MT.
Table 1. Distribution of carbon and oxygen impurities as well as the host element silicon in the initial SS sample.
Spectrum No.
C, wt.%
O, wt.%
Si, wt.%
1
1.43
0.19
98.57
2
1.79
0.31
98.21
3
1.59
0.33
98.41
4
5.82
0.03
93.72
5
1.65
98.35
Mean
2.45
0.21
97.45
Max.
5.82
0.33
98.57
Min.
1.43
0.03
93.72
Table 2. Distribution of carbon and oxygen impurities as well as the host element silicon in the SS sample subjected to MT.
Spectrum No.
C, wt.%
O, wt.%
Si, wt.%
1
10.32
0.50
89.18
2
11.09
0.47
88.44
3
5.00
0.13
94.87
4
4.51
0.21
95.28
Mean
7.73
0.33
91.94
Max.
11.09
0.50
95.28
Min.
4.51
0.13
88.44
Our studies of impurity composition of the SS samples by using X-ray spectroscopy have shown that distribution of carbon and oxygen impurities as well as the host element silicon in the near-surface layers of the SS crystals is non-uniform (Table 1).
The MT somewhat increases the degree of non-uniformity in the distribution of the above-mentioned impurities (Table 2).
As already noted, MT-modified τ2 component remains constant for a long time (230 days). Taking into account the fact that barrier-layer photovoltage (it is the type of photovoltage that we deal with) is generated in chemically heterogeneous and non-uniformly doped semiconductors, one can suppose that the effect of long-lasting invariability of the τ2 component of photovoltage decay in SS after MT may be due to existence of constant (invariable with time) structural inhomogeneity in the bulk part of the SS sample.
At the same time, the effect of long-lasting decrease in the fast component τ1 after MT may be attributed to not only structural inhomogeneity in the bulk part of the SS but also structural inhomogeneity of the surface. In our opinion, it is the defect and impurity state of the surface that changes as time interval between MT termination and measurement of photovoltage decay kinetics rises. Let us dwell on this point in more detail. It is known from literature [9, 10] that, in addition to the process of chemical bond breakage in point defect complexes, magnetic field also stimulates the processes of adsorption and gettering the impurities on MT-activated surface.
An adsorbed particle can be considered as a donor or acceptor impurity. Adsorbed particles may be charged or neutral and may exchange charge carriers with the crystal. So, the process of adsorption can generate new energy levels at the semiconductor interface. It is not inconceivable that, under conditions of our experiment on the MT-activated surface, adsorbed are hydroxyl groups and oxygen from the ambient atmosphere. These adsorbed centers, number of which rises with time, generate additional surface electron states on the Si surface and, consequently, cause a decrease in the charge carrier lifetime during some 30 days after MT termination.
An MT-induced increase in the degree of structural inhomogeneity in SS led not only to changes in the electro-physical characteristics (photovoltage decay kinetics) but also to changes in internal stresses which result in sample bending, i.e. to alteration of the radius of curvature of atomic planes. Complementary studies of sample deformation were carried out by X-ray diffractometric measurements of the curvature of atomic planes. It was found that MT decreases the radius of curvature. The latter may be caused by MT-stimulated process of structural relaxation, which is the reason of a decrease in internal microstresses.
References
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M.I. Molotskiy, Possible mechanism of the magnetoplastic effect // Fizika Tverd. Tela, 33(10), p. 3112 (1991), in Russian.
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A.L. Buchachenko, Magnetoplasticity of diamagnetic crystals in microwave fields // Zhurnal Eksperiment. Teor. Fiziki, 132(3), p. 673-679 (2007), in Russian.
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A.L. Buchachenko, Physical kinetics of magnetoplasticity for diamagnetic crystals // Zhurnal Eksperiment. Teor. Fiziki, 132(4), p. 827-830 (2007), in Russian.
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R.B. Morgunov, Spin micromechanics in the physics of plasticity // Uspekhi Fiz. Nauk, 174(2), p. 131-153 (2004), in Russian.
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Yu.I. Golovin, Magnetoplasticity of solids (Review) // Fizika Tverd. Tela, 46(5), p. 769-803 (2004), in Russian.
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L. Kronik and Y. Shapira, Surface photovoltage techniques: Theory, experiment, and applications // Surf. Sci. Repts. 37(1-5), p. 1-206 (1999).
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V.S. Vavilov, V.F. Kiselev, B.N. Mukashev, Defects in Silicon and on its Surface. Nauka Publ., Moscow, 1990 (in Russian).
9.
V.A. Makara, M.A. Vasilyev, L.P. Steblenko et al. Magnetic-field-induced changes in the impurity state and microhardness of silicon crystals // Fizika Tekhnika Poluprovodnikov, 42(9), p. 1061-1064 (2008), in Russian.
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M.N. Levin, A.V. Tatarintsev, O.A. Kostsov, A.M. Kostsov, Semiconductor surface activation by the action of pulsed magnetic field // Zhurnal Tekhnich. Fiziki, 73(10), p. 85-87 (2003), in Russian.
© 2013, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
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