Self-purification effect in CdTe:Gd crystals
The temperature dependences (T = 80 – 420 K) of the concentration of charge carriers and the Hall mobility in undoped CdTe and CdTe:Gd single crystals grown by the Bridgman method are studied. It is found that the conductivity type of CdTe:Gd crystals changes with increase in the impurity concent...
Збережено в:
| Дата: | 2008 |
|---|---|
| Автори: | , , , , , , |
| Формат: | Стаття |
| Мова: | English |
| Опубліковано: |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2008
|
| Назва видання: | Semiconductor Physics Quantum Electronics & Optoelectronics |
| Онлайн доступ: | http://dspace.nbuv.gov.ua/handle/123456789/118666 |
| Теги: |
Додати тег
Немає тегів, Будьте першим, хто поставить тег для цього запису!
|
| Назва журналу: | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| Цитувати: | Self-purification effect in CdTe:Gd crystals / E.S. Nikonyuk, V.L.Shlyakhovyi, M.O. Kovalets, M.I. Kuchma, Z.I. Zakharuk, A.I. Savchuk, I.M. Yuriychuk // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2008. — Т. 11, № 1. — С. 40-42. — Бібліогр.: 7 назв. — англ. |
Репозитарії
Digital Library of Periodicals of National Academy of Sciences of Ukraine| id |
irk-123456789-118666 |
|---|---|
| record_format |
dspace |
| spelling |
irk-123456789-1186662017-05-31T03:05:53Z Self-purification effect in CdTe:Gd crystals Nikonyuk, E.S. Shlyakhovyi, V.L. Kovalets, M.O. Kuchma, M.I. Zakharuk, Z.I. Savchuk, A.I. Yuriychuk, I.M. The temperature dependences (T = 80 – 420 K) of the concentration of charge carriers and the Hall mobility in undoped CdTe and CdTe:Gd single crystals grown by the Bridgman method are studied. It is found that the conductivity type of CdTe:Gd crystals changes with increase in the impurity concentration in the melt: n-conductivity at 5.10¹⁷ – 3.10¹⁸ cm⁻³ and p-conductivity at 3.10¹⁸ – 10¹⁹ cm⁻³. The concentrations and ionization energies of A₁ (EA₁ = 0.05 eV) and A₂ (EA₂ = 0.12-0.15 eV) acceptors are determined from the temperature dependences of the Hall coefficient and the mobility of carriers. A long-term thermal treatment of gadolinium-doped p-CdTe crystals in the range 663 – 713 K is accompanied by the “self-purification” of the material from A₂- acceptors and compensating donors. The Gd impurity at C₀ > 3.10¹⁸ cm⁻³ is shown to bring no new electrical active centers into the CdTe lattice, by reducing, at the same time, the background of residual impurities. It is suggested that Te precipitates and Te inclusions serve as sinks for the above defects. 2008 Article Self-purification effect in CdTe:Gd crystals / E.S. Nikonyuk, V.L.Shlyakhovyi, M.O. Kovalets, M.I. Kuchma, Z.I. Zakharuk, A.I. Savchuk, I.M. Yuriychuk // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2008. — Т. 11, № 1. — С. 40-42. — Бібліогр.: 7 назв. — англ. 1560-8034 PACS 61.72.Vv, 71.55.-i http://dspace.nbuv.gov.ua/handle/123456789/118666 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| language |
English |
| description |
The temperature dependences (T = 80 – 420 K) of the concentration of charge
carriers and the Hall mobility in undoped CdTe and CdTe:Gd single crystals grown by
the Bridgman method are studied. It is found that the conductivity type of CdTe:Gd
crystals changes with increase in the impurity concentration in the melt: n-conductivity at
5.10¹⁷ – 3.10¹⁸ cm⁻³ and p-conductivity at 3.10¹⁸ – 10¹⁹ cm⁻³. The concentrations and
ionization energies of A₁ (EA₁ = 0.05 eV) and A₂ (EA₂ = 0.12-0.15 eV) acceptors are
determined from the temperature dependences of the Hall coefficient and the mobility of
carriers. A long-term thermal treatment of gadolinium-doped p-CdTe crystals in the
range 663 – 713 K is accompanied by the “self-purification” of the material from A₂-
acceptors and compensating donors. The Gd impurity at C₀ > 3.10¹⁸ cm⁻³ is shown to
bring no new electrical active centers into the CdTe lattice, by reducing, at the same time,
the background of residual impurities. It is suggested that Te precipitates and Te inclusions
serve as sinks for the above defects. |
| format |
Article |
| author |
Nikonyuk, E.S. Shlyakhovyi, V.L. Kovalets, M.O. Kuchma, M.I. Zakharuk, Z.I. Savchuk, A.I. Yuriychuk, I.M. |
| spellingShingle |
Nikonyuk, E.S. Shlyakhovyi, V.L. Kovalets, M.O. Kuchma, M.I. Zakharuk, Z.I. Savchuk, A.I. Yuriychuk, I.M. Self-purification effect in CdTe:Gd crystals Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Nikonyuk, E.S. Shlyakhovyi, V.L. Kovalets, M.O. Kuchma, M.I. Zakharuk, Z.I. Savchuk, A.I. Yuriychuk, I.M. |
| author_sort |
Nikonyuk, E.S. |
| title |
Self-purification effect in CdTe:Gd crystals |
| title_short |
Self-purification effect in CdTe:Gd crystals |
| title_full |
Self-purification effect in CdTe:Gd crystals |
| title_fullStr |
Self-purification effect in CdTe:Gd crystals |
| title_full_unstemmed |
Self-purification effect in CdTe:Gd crystals |
| title_sort |
self-purification effect in cdte:gd crystals |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| publishDate |
2008 |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/118666 |
| citation_txt |
Self-purification effect in CdTe:Gd crystals / E.S. Nikonyuk, V.L.Shlyakhovyi, M.O. Kovalets, M.I. Kuchma, Z.I. Zakharuk, A.I. Savchuk, I.M. Yuriychuk // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2008. — Т. 11, № 1. — С. 40-42. — Бібліогр.: 7 назв. — англ. |
| series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
| work_keys_str_mv |
AT nikonyukes selfpurificationeffectincdtegdcrystals AT shlyakhovyivl selfpurificationeffectincdtegdcrystals AT kovaletsmo selfpurificationeffectincdtegdcrystals AT kuchmami selfpurificationeffectincdtegdcrystals AT zakharukzi selfpurificationeffectincdtegdcrystals AT savchukai selfpurificationeffectincdtegdcrystals AT yuriychukim selfpurificationeffectincdtegdcrystals |
| first_indexed |
2025-07-08T14:25:02Z |
| last_indexed |
2025-07-08T14:25:02Z |
| _version_ |
1837089112767594496 |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2008. V. 11, N 1. P. 40-42.
© 2008, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
40
PACS 61.72.Vv, 71.55.-i
Self-purification effect in CdTe:Gd crystals
E.S. Nikonyuk1, V.L.Shlyakhovyi1, M.O. Kovalets1, M.I. Kuchma1, Z.I. Zakharuk2,
A.I. Savchuk2, I.M. Yuriychuk2
1 National University of Water Management and Conservation, 11, Soborna str.,
35011 Rivne, Ukraine; phone(0362)230420; e-mail: semirivne@mail.ru
2 Chernivtsi National University, 2, Kotsyubynsky str., 58012 Chernivtsi, Ukraine
Phone (0372)584875; e-mail: microel@chnu.cv.ua
Abstract. The temperature dependences (T = 80 – 420 K) of the concentration of charge
carriers and the Hall mobility in undoped CdTe and CdTe:Gd single crystals grown by
the Bridgman method are studied. It is found that the conductivity type of CdTe:Gd
crystals changes with increase in the impurity concentration in the melt: n-conductivity at
5.1017 – 3.1018 cm–3 and p-conductivity at 3.1018 – 1019 cm–3. The concentrations and
ionization energies of A1 (EA1 = 0.05 eV) and A2 (EA2 = 0.12-0.15 eV) acceptors are
determined from the temperature dependences of the Hall coefficient and the mobility of
carriers. A long-term thermal treatment of gadolinium-doped p-CdTe crystals in the
range 663 – 713 K is accompanied by the “self-purification” of the material from A2-
acceptors and compensating donors. The Gd impurity at C0 > 3.1018 cm–3 is shown to
bring no new electrical active centers into the CdTe lattice, by reducing, at the same time,
the background of residual impurities. It is suggested that Te precipitates and Te inclu-
sions serve as sinks for the above defects.
Keywords: semiconductors, cadmium telluride, doping, electron conduction, Hall effect.
Manuscript received 31.10.07; accepted for publication 07.02.08; published online 31.03.08.
1. Introduction
Cadmium telluride has been intensively studied lately as
a promising material for numerous applications
including photonics [1]. Optical and magnetooptical
studies of CdTe doped with Gd reveal several
characteristic properties of the material such as a large
enhancement of the Faraday rotation [2, 3]. To be
integrable in industrial components, semiconductors
need to contain charged scattering centers in low
concentrations. The doping of semiconductor crystals, in
particular of semiconductors of the III-V and IV-VI
groups, with rare-earth elements is accompanied by their
purification from uncontrolled impurities (it is the so-
called “self-purification” effect) [4]. A similar effect is
observed in doped cadmium telluride crystals and has
practically not been studied yet. This paper presents the
electrophysical characterization of CdTe crystals doped
with gadolinium. The effect taking place when the
doping level of CdTe is greater than 3.1018 сm–3 is
discussed.
2. Experimental procedure
Undoped CdTe and CdTe:Gd single crystals were grown
by using the Bridgman method under the same
technological conditions. The doping of cadmium
telluride single crystals with the Gd impurity was carried
out according to the Cd-Te-Gd pattern without excess
tellurium. To avoid the reaction of Gd with quartz even
protected with a pyrolytic graphite layer at high
temperatures, the doping was made during the synthesis.
The master alloy concentration in the melt (C0) varied
from 3.1017 to 3.1019cm–3. The doped crystals have the n-
type conductivity at C0 < 3.1018 сm–3 and the p-type one
at C0 > 3.1018 сm–3. Exactly the p-CdTe-Gd crystals will
be discussed in the present paper. The Gd-doped p-CdTe
crystals were heated (during 24 – 120 h) in evacuated
quartz ampoules.
The temperature dependences (T = 80 – 400 K) of
the concentration of holes (p) and their Hall mobility
(µр) were studied by measuring the Hall coefficient and
the electrical conductivity of samples as functions of the
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2008. V. 11, N 1. P. 40-42.
© 2008, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
41
Table. Long-term thermal treatment (LTT) of CdTe-Gd crystals.
LTT conditions Parameters after LTT
Sample C0, сm–3 g T, K τ, h EA2, eV µ80/µ300 [A2].10–15, сm–3 [A1].10–16, сm–3
1 3.1018 0.33 723 48 0.114 8.4 7.3 3.6
2 3.1018 0.47 693 100 0.135 14.5 7.7 0.3
3 3.1018 0.47 713 72 0.120 11.0 7.3 1.6
4 3.1018 0.47 753 24 0.040 7.3 – 19.0
5 3.1018 0.68 673 100 0.139 13.4 12.0 0.7
6 3.1018 0.68 693 90 0.137 13.0 11.0 1.0
7 3.1018 0.68 753 24 0.043 5.7 – 33.0
8 1019 0.38 673 90 0.150 10.5 7.0 1.3
9 1019 0.86 673 90 0.144 10.0 21.0 1.6
10 3.1019 0.72 673 120 0.152 11.1 15.0 1.6
Note. µ80/µ300 is the ratio between 80 K and room temperature Hall mobilities.
reduced axial coordinate (g) in doped ingots: g = χ/L,
where χ is the coordinate counted from the beginning of
the crystal, and L is the ingot length.
3. Results and discussion
It was found that, in p-CdTe-Gd samples and in CdTe,
the conductivity is controlled only by one acceptor A2
(ionization energy EA2 = 0.12-0.15 eV [5]). The ioniza-
tion energy EA2 is a function of χ at C0 = 3.1018 сm–3 and
remains constant at the heavier doping of the melt
(Fig. 1). Assuming that, in the crystals under study, there
is a modification of A2-acceptors by the presence of Gd
impurity, as was earlier demonstrated for CdTe-Yb
crystals [6], the following suggestions can be made.
First, the coefficient к of the Gd segregation in CdTe is
essentially less than unity and, second, the solubility of
the impurity is so low that, at C0 = 3.1018 сm–3, the
quantuty k·C0 is limited by the boundary solubility. The
low content of the Gd impurity in the main crystal part
(g = 0–0.95) is indicated by the results of magnetic
investigations [3]. Even in the heaviest doped samples at
100 K, the paramagnetic component of the magnetic
susceptibility does not exceed 0.03.10–6 сm3/g, which
gives the value of 1018 сm–3 for the Gd concentration in
the grown crystals. Thus, practically the entire master
alloy is pressed back to the end of ingots (g > 0.95),
where strong paramagnetism is really observed.
The concentrations of A2-acceptors and fully
compensated A1-acceptors as functions of the reduced
axial coordinate g are shown in Figs. 2 and 3. It is seen
that, at g < 0.4, the concentration of A2-acceptors ([A2] =
(5–7).1015 сm–3) is close to that in the undoped crystals.
But, at g > 0.4, it increases abnormally fast, by showing
the tendency to saturate at g > 0.8. The dependence of
[A2] on C0 at g < 0.4, as well as the nonmonotonous
character of this dependence for g > 0.5 for alloys of
different purities, testify that the donor component of the
A2 complex is due to noncontrolled impurities both in the
source components and in Gd.
For low g values, no effect of the impurity on [A1]
can be spotted (Fig. 1). But, at g > 0.4, a “purification”
of the crystal matrix from A1-acceptors due to the
introduction of the Gd impurity occurs. As will be
shown below, this effect is not directly related to the
pressing of A1-acceptors back to the end of the ingot due
to the segregation on the crystallization front, but it is
caused by the transition of A1-acceptors to an electrically
inactive state (precipitation, trapping by other phase
inclusions, in particular, by tellurium, etc. [7]). We
suggest that the Gd impurity intensifies the processes
leading to the formation of tellurium-enriched preci-
pitates and inclusions which serve as sinks for A1-
acceptors. The possibility of such an intensification is
caused by the existence of a series of chemical
compounds (GdTe2, GdTe3), as well as their eutectics
with tellurium in the Gd-Te system. The total concen-
tration of A1-acceptors increases with g. However, the
concentration of sinks increases also, so the [A1](g)
dependence has a nonmonotonous character. The
optimal ratio between the concentrations of the former
and the latter is provided at minimum [A1] values
(g = 0.5–0.7). If this suggestion is correct, then the
thermal treatment of Gd-doped samples depending on
the thermal treatment conditions must be accompanied
both by a further “purification” of the material from A1-
acceptors and by its “contamination”. The effect of a
long-term thermal treatment on the parameters of CdTe-
Gd crystals is given in Table.
The first evident conclusion following from the
above-presented data is that the upper bound of the self-
purification temperature range is lowered as compared
with that of undoped crystals. In particular, the long-
term thermal treatment at 753 K is accompanied by the
full decompensation of A2-acceptors due to a drastic
increase in the concentration of A1-acceptors, which
controls the p-conduction at low temperatures. It turned
out that the higher the values of g and the Gd impurity
concentration in the melt, the stronger the “conta-
mination” of samples with A1-acceptors. After the long-
term thermal treatment at 723 K, the contamination of
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2008. V. 11, N 1. P. 40-42.
© 2008, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
42
samples with A1-acceptors is less noticeable, and A2-
acceptors continue to control the conductivity. Hence, it
can be asserted that the upper temperature bound of the
effective “self-purification” of Gd-doped samples does
not exceed 713 K.
The lowest concentrations of A1-acceptors were
obtained after the long-term thermal treatment at 673–
693 K on samples containing the smallest amounts of
Gd. The temperature area of the effective “self-
purification” was then shifted even lower, but the
samples required a very long thermal treatment. We note
that the “self-purification” effect during a long-term
thermal treatment is always accompanied by an increase
in the ionization energy of A2-acceptors, which testifies
that the “purification” from compensating donors occurs
simultaneously. No unambiguous conclusions can be
made as for the “self-purification” from A2-acceptors,
since changes in [A2] under a long-term thermal
treatment are relatively small.
4. Conclusion
A long-term thermal treatment (τ = 100 h) of Gd-doped
p-CdTe crystals in the temperature region of 663–713 K
is accompanied by the “self-purification” of the material
from A2-acceptors and compensating donors. Precipitates
and inclusions containing tellurium serve as sinks for the
polluting species. The temperature decrease in the area
of the effective “self-purification” is caused by the
enrichment of sinks with gadolinium forming com-
pounds with Te. In particular, the eutectic temperature of
GdTe3+Te equal to 673 K gets just into the “self-
purification” area.
References
1. R. Triboulet, Fundamentals of the CdTe synthesis //
J. Alloys and Compounds 371 (1-3), p. 67-71
(2004).
2. A.I. Savchuk, S.Yu. Paranchych, V.M. Frasunyak,
V.I. Fediv, Yu.V. Tanasyuk, Y.O. Kandyba,
P.I. Nikitin, Optical and magnetooptical study of
CdTe crystals doped with rare earth ions // Mater.
Sci. Eng.B 105 (1-3), p. 161-164 (2003).
3. A.I. Savchuk, V.M. Frasunyak, Y.O. Kandyba,
T.A. Savchuk, P.I. Nikitin, Giant Faraday rotation
in CdTe spin-doped with rare earth ions // Phys.
status solidi (b) 229(2), p. 787-790 (2002).
4. D.M. Zayachuk, D.D. Ivanchuk, R.D. Ivanchuk,
The effect of gadolinium doping on the physical
properties of lead telluride // Phys. status solidi (a)
119(1), p. 215-220 (1990).
5. E.S. Nikonyuk, V.L. Shlyakhovyi, Z.I. Zakharuk,
M.O. Kovalets, M.I. Kuchma, Self-purification in
p-CdTe crystals at thermal treatment // Neorganich.
Materialy 31(2), p. 185-187 (1995) (in Russian).
6. E.S. Nikonyuk, V.L. Shlyakhovyi, M.O. Kovalets,
Z.I. Zakharuk, M.I. Kuchma, A-centers modifying
in CdTeYb crystal // J. Cryst. Growth 161(1),
p. 186-189 (1996).
7. J.L. Pautrat, N. Magnea, J.P. Faurie, The segre-
gation of impurities and the self-compensation
problem in II-VI compounds // J. Appl. Phys.
53(12), p. 8668-8677 (1982).
Fig. 1. Axial distribution of the ionization energy of A2-
acceptors in p-CdTe-Gd crystals for different C0 values: 1 –
3.1018; 2 – 1019; 3 – 3.1019 cm–3.
Fig. 2. Axial distribution of the concentration of A2-
acceptors in p-CdTe-Gd crystals for different C0 values:
1 – 3.1018; 2 – 1019; 3 – 3.1019 cm–3.
Fig. 3. Axial distribution of the concentration of A1-
acceptors in p-CdTe-Gd crystals for different C0 values:
1 – 3.1018; 2 – 1019; 3 – 3.1019 cm–3 ; 4 – undoped CdTe.
|