Electric properties of TlInS₂ single crystals
Injection currents are studied in high-resistive layer of TlInS2 single crystals and the following parameters were determined: equilibrium concentration of charge carriers in the allowed band p0 = 1.67⋅10¹⁰ cm⁻³; concentration of traps Nt = 10¹²cm⁻³; capture factor θ = 0.17; mobility of charge carri...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2006
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| Назва видання: | Semiconductor Physics Quantum Electronics & Optoelectronics |
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| Цитувати: | Electric properties of TlInS₂ single crystals / S.N. Mustafaeva, A.A. Ismailov, N.D. Akhmedzade // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2006. — Т. 9, № 4. — С. 82-84. — Бібліогр.: 4 назв. — англ. |
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irk-123456789-1216402017-06-16T03:03:38Z Electric properties of TlInS₂ single crystals Mustafaeva, S.N. Ismailov, A.A. Akhmedzade, N.D. Injection currents are studied in high-resistive layer of TlInS2 single crystals and the following parameters were determined: equilibrium concentration of charge carriers in the allowed band p0 = 1.67⋅10¹⁰ cm⁻³; concentration of traps Nt = 10¹²cm⁻³; capture factor θ = 0.17; mobility of charge carriers μ = 3.3⋅10⁻³cm²/V⋅s; the depth of trap level responsible for the injection current Et = 0.44 eV. 2006 Article Electric properties of TlInS₂ single crystals / S.N. Mustafaeva, A.A. Ismailov, N.D. Akhmedzade // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2006. — Т. 9, № 4. — С. 82-84. — Бібліогр.: 4 назв. — англ. 1560-8034 PACS 71.20.Nr; 72.20Fr; 72.20.Ht; 72.20 Jv http://dspace.nbuv.gov.ua/handle/123456789/121640 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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Injection currents are studied in high-resistive layer of TlInS2 single crystals and the following parameters were determined: equilibrium concentration of charge carriers in the allowed band p0 = 1.67⋅10¹⁰ cm⁻³; concentration of traps Nt = 10¹²cm⁻³; capture factor θ = 0.17; mobility of charge carriers μ = 3.3⋅10⁻³cm²/V⋅s; the depth of trap level responsible for the injection current Et = 0.44 eV. |
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Article |
| author |
Mustafaeva, S.N. Ismailov, A.A. Akhmedzade, N.D. |
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Mustafaeva, S.N. Ismailov, A.A. Akhmedzade, N.D. Electric properties of TlInS₂ single crystals Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Mustafaeva, S.N. Ismailov, A.A. Akhmedzade, N.D. |
| author_sort |
Mustafaeva, S.N. |
| title |
Electric properties of TlInS₂ single crystals |
| title_short |
Electric properties of TlInS₂ single crystals |
| title_full |
Electric properties of TlInS₂ single crystals |
| title_fullStr |
Electric properties of TlInS₂ single crystals |
| title_full_unstemmed |
Electric properties of TlInS₂ single crystals |
| title_sort |
electric properties of tlins₂ single crystals |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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2006 |
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http://dspace.nbuv.gov.ua/handle/123456789/121640 |
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Electric properties of TlInS₂ single crystals / S.N. Mustafaeva, A.A. Ismailov, N.D. Akhmedzade // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2006. — Т. 9, № 4. — С. 82-84. — Бібліогр.: 4 назв. — англ. |
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Semiconductor Physics Quantum Electronics & Optoelectronics |
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2025-07-08T20:15:54Z |
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1837111186529714176 |
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Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 4. P. 82-84.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
82
PACS 71.20.Nr; 72.20Fr; 72.20.Ht; 72.20 Jv
Electric properties of TlInS2 single crystals
S.N. Mustafaeva, A.A. Ismailov, N.D. Akhmedzade
Institute of Physics, Azerbaijan National Academy of Sciences
AZ 1143 Baku, G. Javid avenue, 33
E-mail: asadov_salim@mail.ru
Abstract. Injection currents are studied in high-resistive layer of TlInS2 single crystals
and the following parameters were determined: equilibrium concentration of charge
carriers in the allowed band p0 = 1.67⋅1010 cm−3; concentration of traps Nt = 1012cm−3;
capture factor θ = 0.17; mobility of charge carriers μ = 3.3⋅10−3cm2/V⋅s; the depth of trap
level responsible for the injection current Et = 0.44 eV.
Keywords: injection current, single crystal, charge transport, space charge, capture
factor.
Manuscript received 07.02.06; accepted for publication 23.10.06.
1. Introduction
TlInS2 single crystals are typical representatives of
layered wide-gap semiconductors that are characterized
by the low mobility of current carriers. Such materials
are very perspective for creating solid state electron
devices on their base.
Layered crystals usually contain structural defects,
such as dislocations and vacancies. The presence of
these defects results in a high density of localized states
near the Fermi level.
Studying the charge transport processes in layer
TlInS2 single crystals at constant and an alternating
current has shown that at low temperatures (T < 200 K)
and frequencies f = 105…106 Hz the hopping conduc-
tivity on localized near the Fermi level states takes place
in them [1, 2].
In semiconductors with a high density of localized
states in the vicinity of the Fermi level, the hopping con-
ductivity in the forbidden band in a constant electric field
and at low temperatures dominates over the conductivity
caused by thermoactivated charge carriers in the allowed
band. However, near the room temperature and above
charge transport in semiconductors at a direct current
basically occurs in the allowed band.
It was of interest to study non-ohmic conductivity
in the allowed band of TlInS2 single crystal and to
establish the mechanism of charge transport, which was
the purpose of this work.
2. Experimental results and discussion
Samples from TlInS2 for measurements were obtained
by spalling along C-axis of the natural spall from
massive single crystal and had the thickness
(200…280) μm. TlInS2 samples formed flat capacitors
whose plane was perpendicular to the crystalline C-axis.
The capacitor plate area was (4…6)⋅10−2 cm2. Ohmic
contacts of samples were made using Ag paste.
In the figure, current-voltage characteristics (CVC)
of Ag-TlInS2-Ag sample are shown at the temperatures
293 (curve 1); 307 (2); 341 (3) and 381 K (4). CVCs at
all the temperatures were characterized by enough long
quadratic portion (I ∼ V 2). At the temperatures 293, 307,
and 341 K the square-law portion was preceded with
short ohmic portion (I ∼ V). And at 381 K for all the
investigated electric voltages I ∼ V 2. At 293 K, the CVC
is characterized with super linear portion (I ∼ V6.5) after
the quadratic portion.
The experimental results obtained in this study
were interpreted within the Lampert theory for an
electric current limited by the space charge (SCLC) [3].
In semiconductors, this theory allows to receive
data on local levels in the forbidden band. Local levels
render strong influence on the injection current caused
by an external electric voltage. Thus, local states define
not only change of a current, for example, reduction of
an injection current owing to localization of charge
carriers, but also the shape of CVC.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 4. P. 82-84.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
83
Within the limits of the SCLC theory in
semiconductors with traps at times of flight of carriers
through the semiconductor, exceeding times of capture
for traps, up to a voltage of full filling of traps the
current limited by space charge should flow, expression
for which is as follows [3]:
,
8
9
3
2
0
L
VI θμεε= (1)
where ε0 is the dielectric constant; ε is the dielectric
permittivity of a crystal; θ is the capture factor; L is the
thickness of a crystal; μ is the mobility of charge
carriers; V is the applied electric voltage. At achieve-
ment of a voltage of full filling of traps (Vf) on the CVC
of TlInS2 sample, there is a portion of abrupt growth of
the current (Figure, curve 1). In this case, determining
from experiment Vf, we have calculated concentration of
traps under the formula:
2
6101.1
L
V
N f
t
ε
⋅= , (2)
Nt = 1012 cm−3. We also determined the value of the
equilibrium concentration of the basic charge carriers
p0 = 1.67⋅1010 cm−3 in TlInS2 from the relation of the
currents corresponding to two voltages Vf and 2Vf [3]:
)2(
)(
0
f
ft
VI
VIN
p = . (3)
For the sample of TlInS2 single crystal at 293 K,
we have determined also the factor of capture:
xV
Lp
ε
θ
2
06108.1 −⋅= , (4)
which was equal to 0.17. In calculations for the dielec-
tric permittivity of TlInS2 single crystal, the value ε = 10
determined experimentally in [2] was taken. In the
formula (4), Vx is such a voltage, at which the concen-
tration of free injected charge carriers becomes
comparable with the equilibrium concentration, in other
words, it is a voltage of transition from an ohmic portion
of CVC to the square-law one. Knowing the specific
dark conductivity of TlInS2 single crystal sample at
293 K σ0 = 10−11 Ohm−1cm−1, under the formula
σ0 = p0eμ0 (5)
we have calculated the mobility of holes at the voltages
corresponding to the ohmic portion of CVC: μ0 =
3.7⋅10−3 cm2/V⋅s. Using experimental results under the
formula (1), we have estimated the mobility of carriers at
the voltages corresponding to the square-law portion of
CVC for TlInS2 single crystal: μ = 3.3⋅10−3 cm2/V⋅s.
Apparently, both values of mobility, i.e. μ0 and μ,
practically coincide.
Knowing values of Nt and θ under the formula
t
p
t N
N
kTE
θ2
ln= , (6)
where Np is the effective density of quantum states in the
allowed band of a crystal (∼1019 cm−3), we have
estimated the depth of the local level responsible for an
injection current: Et = 0.44 eV. The level with the
activation energy ∼0.4 eV has been also revealed from
the temperature dependence of the ohmic conductivity
across layers of TlInS2 single crystal [1] and from
spectra of a photocurrent [4].
Absence an abrupt portion on CVC of Ag-TlInS2-
Ag sample at T > 300 K is connected with the fact that at
these temperatures thermal emission of charge carriers
began from a level 0.4 eV to the allowed band and full
filling of traps did not manage to be achieved (Figure,
curves 2-4).
An important feature of the current limited by the
space charge is that the electric charge in this case
cannot exceed the quantity CgV, where Cg is the
geometric capacitance of the sample and V is the voltage
imposed across the sample. For the samples studied in
this work, the geometric capacitance was estimated as
∼10−12 F.
The maximum voltage across the sample amounted
to 150 V. This means that the electric charge of the
system Ag-TlInS2-Ag is equal to 1.5⋅10–10 C. The charge
per unit area Qmax allowed to be transported by the space
charge limitations is 3.8⋅10−9 C/cm2.
Illumination of TlInS2 sample, in which the current
of monopolar injection was supported by white light,
leads to increase of SCLC (see Figure, curve 5).
Figure. Current-voltage characteristics of dark (curves 1-4)
and photocurrent (curve 5) of Ag-TlInS2-Ag system. Curves 1
and 5 were measured at the temperatures 293 K; 2 – 304, 3 –
341, 4 – 381.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 4. P. 82-84.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
84
It testifies that the carriers injected from the contact
and grasped on traps, absorb photons and are thrown out
to the allowed band. I.e., under influence of light the
space charge is redistributed between states, on which
there is a transport, and states, in which there are grasped
carriers.
Thus, the full space charge in a crystal remains
constant; it is determined by the applied voltage and
geometry of the sample. It is seen from Figure that a
photocurrent limited by space charge (curve 5), also as
well as dark SCLC, changes as V 2, that is in the consent
with SCLC theory.
Near to a voltage of full filling of traps, the
dependence of a photocurrent on a voltage weakens,
CVCs of dark and photocurrent (curves 1 and 5) are
crossed, and then the photocurrent is saturated and
ceases to depend on a voltage.
Saturation of a photocurrent with an electric field
increase speaks about an exhaustion of the ohmic
contact: in high electric fields the contact is not capable
to provide any more sufficient number of electrons for
establishment of SCLC in volume. I.e., the centers of
capture of charge carriers essentially influence on a
photocurrent. In this connection, the effects connected
with capture of charge carriers determine the sensitivity
and operating speed of semiconductor devices.
References
1. S.N. Mustafaeva, Non-activated hopping conduc-
tivity in TlInS2 single crystals // Izvestiya NANA.
Ser. fiz. tekhn. i mat. nauk (Baku) 24 (5), p. 106-
108 (2004).
2. S.N. Mustafaeva, M.M. Asadov, V.A. Ramazan-
zade, Dielectric properties and ac-conductivity of
TlInS2 single crystals // Fizika tverdogo tela 38(1),
p. 14-18 (1996) (in Russian).
3. M. Lampert, P. Mark, Current injection in solids.
Academic Press, New York and London, 1970.
4. S.N. Mustafaeva, M.M. Asadov, V.A. Ramazan-
zade, Modification of photocurrent spectra of
TlInS2 single crystals at intercalation //
Neorganich. Materialy 31(3) p. 318-320 (1995) (in
Russian).
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