Long-term relaxation of photoconductivity in cadmium doped Gd₂S₃ films
In first time it is experimentally investigated some regularities of long-term relaxation of photoconductivity of gadolinium one-and-halp sulfides thin films doped by cadmium atoms. Was calculated maximum of recombination barrier and found the location of trapping levels in the gap. Вперше експериме...
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Науковий фізико-технологічний центр МОН та НАН України
2011
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| Cite this: | Long-term relaxation of photoconductivity in cadmium doped Gd₂S₃ films / Z.U. Jabua, A.V. Gigineishvili, I.G. Tabatadze, I.L. Kupreishvili // Физическая инженерия поверхности. — 2011. — Т. 9, № 1. — С. 44–47. — Бібліогр.: 10 назв. — англ. |
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| author | Jabua, Z.U. Gigineishvili, A.V. Tabatadze, I.G. Kupreishvili, I.L. |
| author_facet | Jabua, Z.U. Gigineishvili, A.V. Tabatadze, I.G. Kupreishvili, I.L. |
| citation_txt | Long-term relaxation of photoconductivity in cadmium doped Gd₂S₃ films / Z.U. Jabua, A.V. Gigineishvili, I.G. Tabatadze, I.L. Kupreishvili // Физическая инженерия поверхности. — 2011. — Т. 9, № 1. — С. 44–47. — Бібліогр.: 10 назв. — англ. |
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| description | In first time it is experimentally investigated some regularities of long-term relaxation of photoconductivity of gadolinium one-and-halp sulfides thin films doped by cadmium atoms. Was calculated maximum of recombination barrier and found the location of trapping levels in the gap.
Вперше експериментально досліджені деякі закономірності довгострокової релаксації фотопровідності плівок полуторного сульфіду гадолінія, які леговані атомами кадмію. Розраховано максимальне значення рекомбінаційного бар’єру та встановлено розташування рівнів прилипання в забороненій зоні.
Впервые экспериментально исследованы некоторые закономерности долговременной релаксации фотопроводимости плёнок полуторного сульфида гадолиния, легированных атомами кадмия. Рассчитано максимальное значение рекомбинационного барьера и установлено расположение уровней прилипания в запрещённой зоне.
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44
INTRODUCTION
One-and-a-half sulfides of rare-earth elements
(REE) concern to wide-band semiconductors [1].
In these connections are observed variety
interesting, small studied effects, which are per-
spective for practical application for optoelect-
ronis devices [2 – 6]. To such effects concerns
so called a long-term relaxation (LTR) of photo-
conductivity (FC). It is considered that LTR is
connected with existence in investigated object
potential barrier, which are in turn caused by in
homogeneity of material. As it is known, one-
and-a-half sulfides REE are characterized by pre-
sence in them own statistically distributed struc-
tural defects (in caution sublattice every ninth
knot is vacancy [7]). It is possible to assume that
such imperfections will play a part in process of
LTR of photoconductivity.
In the given work some experimental laws of
LTR in films of Gd2S3 alloyed by atoms of cad-
mium are presented.
EXPERIMENTAL
Polycrystalline films of Gd2S3 0.6 – 4.4 mm
in thikness were made by thermal evaporated
from two independent sources of Gd and S [8].
Electronographical and X-ray analyze showed
that thin films had cubical crystal structure of
Th3p4 type (γ-form, space group of In3d) with lat-
tice parameters a = 8.34 D, which is in good ag-
reement with lattice parameters of bulk crystals
of Gd2S3 [7]. All films had high specific resis-
tivity – ~1010 Ohm⋅cm. In order to reduce resis-
tivity the samples are doped with cadmium
atoms. Doping was done from gas phase in clo-
sed volume by a technique described in [8]. After
doping, as have shown X-ray and electronogra-
phical analysis all films were single-phase, had
n-type conductivity and specific resistivity –
~102 – 103 Ohm⋅cm.
Experiments on studying temperature, spec-
tral, time and luxsampere dependences of resis-
tance were spent on installation КСВУ-23 equip-
ped with the micro-computer, which was used
for management of experiment and processing
of the saved up data.
RESULTS AN DISCUSSION
As have shown experiments on studying of
kinetics photoconductivity (fig. 1), long-term
processes accompany not only de-energizing but
also induction of monochromatic illumination.
It is known that the hearth of a LTR lies space
division of nonequillibrium carriers of a charge
PACS: 7350 Pz.7361 Le.7840 Fy
LONG-TERM RELAXATION OF PHOTOCONDUCTIVITY IN CADMIUM
DOPED Gd2S3 FILMS
Z.U. Jabua, A.V. Gigineishvili, I.G. Tabatadze, I.L. Kupreishvili
Department of Physiscs Georgian Techical Univerisity (Tbilisi)
Georgia
Received 21.02.2011
In first time it is experimentally investigated some regularities of long-term relaxation of photo-
conductivity of gadolinium one-and-halp sulfides thin films doped by cadmium atoms. Was calculated
maximum of recombination barrier and found the location of trapping levels in the gap.
Keywords: film, sulfide, photoconductivity, relaxation, acceptor, barrier.
Вперше експериментально досліджені деякі закономірності довгострокової релаксації фото-
провідності плівок полуторного сульфіду гадолінія, які леговані атомами кадмію. Розраховано
максимальне значення рекомбінаційного бар’єру та встановлено розташування рівнів прили-
пання в забороненій зоні.
Ключові слова: плівка, сульфід, фотопровідність, релаксація, акцептор, бар’єр.
Впервые экспериментально исследованы некоторые закономерности долговременной релак-
сации фотопроводимости плёнок полуторного сульфида гадолиния, легированных атомами
кадмия. Рассчитано максимальное значение рекомбинационного барьера и установлено рас-
положение уровней прилипания в запрещённой зоне.
Ключевые слова: плёнка, сульфид, фотопроводимость, релаксация, акцептор, барьер.
Jabua Z.U., Gigineishvili A.V., Tabatadze I.G., Kupreishvili I.L., 2011
45ФІП ФИП PSE, 2011, т. 9, № 1, vol. 9, No. 1
by electric fields of inhomogeneithy an investi-
gated materials. In this connection, naturally, the
recombination in interfaced to necessity of over-
coming of a potential barrier EB, and time of life
of nonequellibrium carrier of a charge is calcu-
lated by the formula
τ = 0exp(EB/kT). (1)
Stationary concentration is expressed by the
formula
∆n = ∆βτJ ,
where α is coefficient of absorption, β – quantum
exit, J – intensity of light. It is natural to admit
that division of carriers of a charge creates
electric fields inhomogeneity in this connection
energy potential barrier with growth of stationary
concentration will decreases.
Naturally, instant times of a relaxation should
grow linearly with time increase, as it is shown
in work [9]. Value of instant times of a relaxation
(fig. 2) we have defined on an inclination of
tangents to relaxation curves. From fig. 2. it is
visible that characterizing these two processes
instant times have very close values. The big
size of life time (> 105 s), of nonequillibrium
carriers of a charge, leads to that after a while
de-energizing of monochromatic radiation,
falling on the sample, conductivity of a film
changes and remains essentially above it darking
values. The described phenomenon is considered
as residual conductivity [9], sometimes it name
spectral memory conductivity aspires to satura-
tion.
Luxsampere characteristics of photocon-
ductivity and residual conductivity are shown on
fig. 3. It is known [10] that at small intensitys of
illumination size of photoconductivity and resi-
dual conductivity linearly grow, and at big when
stationary concentration nonequillibrium essen-
tially changes size potential barrier, stationary
values of photoconductivity show sublinear
character, and the size of residual.
Fig. 1. Cinetics of photoconductivity at 98 К (λ=450 nm,
I = Vt/cm2 by a dotted line accepts the illumination termi-
nation).
Fig. 2. Characteristis times of a relaxation (1) and an es-
tablishment of stationary value of photoconductivity (2),
relaxation curves of residual conductivity at Т = 104 K
(3) and T = 121 K (4).
Fig. 3. Dependence of photoconductivity (1) and residual
conductivity (2) from intensity of radiation at 112 K
(λ = 470 nm).
Z.U. JABUA, A.V. GIGINEISHVILI, I.G. TABATADZE, I.L. KUPREISHVILI
46
The analysis of relaxation curves of residual
conductivity at various temperatures (fig. 2) has
shown that the size potential barrier is expressed
by the formula
[ ]1 2 1
1 2
2
ln
B
TT k TE T T
T
= −
.
During a relaxation at accepts value 0.13 –
0.27 eV. It is obvious that darking value of EB
it is even more.
Measurement of FC and residual conductivity
of Gd2S3:Cd film spent to areas of energy of pho-
tons 1.5 – 4.2 eV at temperature 98 K (fig. 4).
Exceeding background of the photoresponse is
marked above energy of illumination 1.6 eV. On
all spectrum identical frequency rate of change
FC an residual conductivity is observed.
The long-wave edge of FC most likely is con-
nected with acceptor levels in impurity zone.
The peak of FC at energy 2.63 eV, is obviously
caused with excitation of a charge carrier from
a valency zone in donor zone. Carrying outh that
analysis of position of this transition and red
border of FC, it is possible to estimate energy of
ionization of acceptor the level formed by va-
cancies Gd – 0.85 eV. The structure of energy
2.93 eV, possibly is caused by interzone tran-
sition of electrons and will well be coordinated
by power position with the data optical research.
CONCLUSION
In films of Gd2S3 alloyed by atoms of cadmium,
are studied kinetics of photoconductivity and
processes of a long-term relaxation. It is shown
that the long-wave edge of photoconductivity is
connected with transitions of electrons from
compensated deep acceptor levels in impurity
zone. Energy of ionization of the acceptor levels,
formed by vacancies of the gadolinium atoms,
are estimated.
The received experimental data say that thin
films of one-and-a-half sulfide of a gadolinium
alloyed by atoms of cadmium can be perspective
materials for creation of photosensitive devices.
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ФІП ФИП PSE, 2011, т. 9, № 1, vol. 9, No. 1
LONG-TERM RELAXATION OF PHOTOCONDUCTIVITY IN CADMIUM DOPED Gd2S3 FILMS
47ФІП ФИП PSE, 2011, т. 9, № 1, vol. 9, No. 1
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|
| id | nasplib_isofts_kiev_ua-123456789-76139 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1999-8074 |
| language | English |
| last_indexed | 2025-12-07T17:37:27Z |
| publishDate | 2011 |
| publisher | Науковий фізико-технологічний центр МОН та НАН України |
| record_format | dspace |
| spelling | Jabua, Z.U. Gigineishvili, A.V. Tabatadze, I.G. Kupreishvili, I.L. 2015-02-08T07:57:59Z 2015-02-08T07:57:59Z 2011 Long-term relaxation of photoconductivity in cadmium doped Gd₂S₃ films / Z.U. Jabua, A.V. Gigineishvili, I.G. Tabatadze, I.L. Kupreishvili // Физическая инженерия поверхности. — 2011. — Т. 9, № 1. — С. 44–47. — Бібліогр.: 10 назв. — англ. 1999-8074 PACS: 7350 Pz.7361 Le.7840 Fy https://nasplib.isofts.kiev.ua/handle/123456789/76139 In first time it is experimentally investigated some regularities of long-term relaxation of photoconductivity of gadolinium one-and-halp sulfides thin films doped by cadmium atoms. Was calculated maximum of recombination barrier and found the location of trapping levels in the gap. Вперше експериментально досліджені деякі закономірності довгострокової релаксації фотопровідності плівок полуторного сульфіду гадолінія, які леговані атомами кадмію. Розраховано максимальне значення рекомбінаційного бар’єру та встановлено розташування рівнів прилипання в забороненій зоні. Впервые экспериментально исследованы некоторые закономерности долговременной релаксации фотопроводимости плёнок полуторного сульфида гадолиния, легированных атомами кадмия. Рассчитано максимальное значение рекомбинационного барьера и установлено расположение уровней прилипания в запрещённой зоне. en Науковий фізико-технологічний центр МОН та НАН України Физическая инженерия поверхности Long-term relaxation of photoconductivity in cadmium doped Gd₂S₃ films Article published earlier |
| spellingShingle | Long-term relaxation of photoconductivity in cadmium doped Gd₂S₃ films Jabua, Z.U. Gigineishvili, A.V. Tabatadze, I.G. Kupreishvili, I.L. |
| title | Long-term relaxation of photoconductivity in cadmium doped Gd₂S₃ films |
| title_full | Long-term relaxation of photoconductivity in cadmium doped Gd₂S₃ films |
| title_fullStr | Long-term relaxation of photoconductivity in cadmium doped Gd₂S₃ films |
| title_full_unstemmed | Long-term relaxation of photoconductivity in cadmium doped Gd₂S₃ films |
| title_short | Long-term relaxation of photoconductivity in cadmium doped Gd₂S₃ films |
| title_sort | long-term relaxation of photoconductivity in cadmium doped gd₂s₃ films |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/76139 |
| work_keys_str_mv | AT jabuazu longtermrelaxationofphotoconductivityincadmiumdopedgd2s3films AT gigineishviliav longtermrelaxationofphotoconductivityincadmiumdopedgd2s3films AT tabatadzeig longtermrelaxationofphotoconductivityincadmiumdopedgd2s3films AT kupreishviliil longtermrelaxationofphotoconductivityincadmiumdopedgd2s3films |