Electrical properties of n-SnS₂/n-CdIn₂Te₄ heterostructure
Using the method of deposition over the optical contact, the authors created nSnS2/n-CdIn₂Te₄ heterojunction and investigated temperature evolution of its currentvoltage characteristics under the forward bias U ≤ 3 V. Analyzing temperature dependence of the curves obtained, the main mechanisms of...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2010
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irk-123456789-1187392017-06-01T03:05:36Z Electrical properties of n-SnS₂/n-CdIn₂Te₄ heterostructure Gorley, P.M. Grushka, Z.M. Grushka, O.G. Gorley, P.P. Zabolotsky, I.I. Using the method of deposition over the optical contact, the authors created nSnS2/n-CdIn₂Te₄ heterojunction and investigated temperature evolution of its currentvoltage characteristics under the forward bias U ≤ 3 V. Analyzing temperature dependence of the curves obtained, the main mechanisms of current transport through the semiconductor contact were determined, allowing prediction of successful possible applications of the heterojunction studied under high temperatures and elevated radiation due to the parameters of the base semiconductors and the diode structure itself. 2010 Article Electrical properties of n-SnS₂/n-CdIn₂Te₄ heterostructure / P.M. Gorley, Z.M. Grushka, O.G. Grushka, P.P. Gorley, I.I. Zabolotsky // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2010. — Т. 13, № 4. — С. 444-447. — Бібліогр.: 14 назв. — англ. 1560-8034 PACS 73.40.Cg, Gk, Lq http://dspace.nbuv.gov.ua/handle/123456789/118739 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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English |
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Using the method of deposition over the optical contact, the authors created nSnS2/n-CdIn₂Te₄
heterojunction and investigated temperature evolution of its currentvoltage
characteristics under the forward bias U ≤ 3 V. Analyzing temperature
dependence of the curves obtained, the main mechanisms of current transport through the
semiconductor contact were determined, allowing prediction of successful possible
applications of the heterojunction studied under high temperatures and elevated radiation
due to the parameters of the base semiconductors and the diode structure itself. |
| format |
Article |
| author |
Gorley, P.M. Grushka, Z.M. Grushka, O.G. Gorley, P.P. Zabolotsky, I.I. |
| spellingShingle |
Gorley, P.M. Grushka, Z.M. Grushka, O.G. Gorley, P.P. Zabolotsky, I.I. Electrical properties of n-SnS₂/n-CdIn₂Te₄ heterostructure Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Gorley, P.M. Grushka, Z.M. Grushka, O.G. Gorley, P.P. Zabolotsky, I.I. |
| author_sort |
Gorley, P.M. |
| title |
Electrical properties of n-SnS₂/n-CdIn₂Te₄ heterostructure |
| title_short |
Electrical properties of n-SnS₂/n-CdIn₂Te₄ heterostructure |
| title_full |
Electrical properties of n-SnS₂/n-CdIn₂Te₄ heterostructure |
| title_fullStr |
Electrical properties of n-SnS₂/n-CdIn₂Te₄ heterostructure |
| title_full_unstemmed |
Electrical properties of n-SnS₂/n-CdIn₂Te₄ heterostructure |
| title_sort |
electrical properties of n-sns₂/n-cdin₂te₄ heterostructure |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| publishDate |
2010 |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/118739 |
| citation_txt |
Electrical properties of n-SnS₂/n-CdIn₂Te₄ heterostructure / P.M. Gorley, Z.M. Grushka, O.G. Grushka, P.P. Gorley, I.I. Zabolotsky // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2010. — Т. 13, № 4. — С. 444-447. — Бібліогр.: 14 назв. — англ. |
| series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
| work_keys_str_mv |
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2025-07-08T14:33:53Z |
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2025-07-08T14:33:53Z |
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1837089673240903680 |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2010. V. 13, N 4. P. 444-447.
© 2010, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
444
PACS 73.40.Cg, Gk, Lq
Electrical properties of n-SnS2/n-CdIn2Te4 heterostructure
P.M. Gorley 1, Z.M. Grushka1, O.G. Grushka1, P.P. Gorley1,2, I.I. Zabolotsky1
1Yu. Fedkovych Chernivtsi National University,
2, Kotsyubynsky str., 58012 Chernivtsi, Ukraine,
Phone: +38 03722 46877, fax: +38 03722 46877,
E-mail: semicon-dpt@chnu.edu.ua
2Centro de Física das Interacções Fundamentais,
Av. Rovisco Pais, 1049-001 Lisboan, Portugal
Phone: +351 21 8419690, e-mail: pphorley@cfif.ist.utl.pt
Abstract. Using the method of deposition over the optical contact, the authors created n-
SnS2/n-CdIn2Te4 heterojunction and investigated temperature evolution of its current-
voltage characteristics under the forward bias U ≤ 3 V. Analyzing temperature
dependence of the curves obtained, the main mechanisms of current transport through the
semiconductor contact were determined, allowing prediction of successful possible
applications of the heterojunction studied under high temperatures and elevated radiation
due to the parameters of the base semiconductors and the diode structure itself.
Keywords: heterojunction, n-SnS2/n-CdIn2Te4, optical contact, current-voltage curve,
current transport mechanisms.
Manuscript received 30.12.09; accepted for publication 02.12.10; published online 30.12.10.
1. Introduction
At the modern development stage of electronics, it is
especially timely and important task to create devices
able to operate under the significant fluxes of ionizing
radiation, and also at the elevated temperatures without
additional cooling. Among these devices, one should
mention rectifying structures based on layered
semiconductors and materials with the stoichiometric
vacancies (see, e.g., paper [1] and references therein).
This is caused by the fact that layered semiconductors
(including SnS2) possess many unique physical and
chemical properties [2]. In particular, predominant Van-
der-Waals binding between the layers allows the
possibility to obtain thin and quite elastic plates with
mirror-smooth and practically ideal surface [2, 3] by
simple material chipping from the monocrystalline
ingots. Another technologically-important detail
concerns the ability to create heterojunction to the
layered semiconductors by deposition over the optical
contact. This method does not require high-temperature
treatment and yields good adhesion of the junction
components, approaching bulk durability of the
contacting materials [4].
The beneficial peculiarities of materials with the
so-called defect semiconductor phases (including
Hg3In2Te6 and CdIn2Te4) is the large concentration of
stoichiometric vacancies (up to ~ 321cm10 [5]), which
causes high semiconductor stability towards the action of
ionizing radiation [1, 6]. The latter phenomenon attracts
significant interest to the defect phases as promising
materials for creation of the photosensitive structures,
able to operate under high temperatures without any
additional cooling.
This paper presents the results concerning tech-
nology for n-SnS2/n-CdIn2Te4 heterojunctions using the
methodology of deposition over optical contact, as well as
the detailed study of their current-voltage characteristics
(CVC) under the forward bias. Using the Anderson model
[7] for the sharp heterojunction, we have estimated the
height of the potential barrier within heterostructure,
determined the dominating current transport mechanisms
of transformation between them upon application of a
different voltage. The obtained results allowed to
conclude that n-SnS2/n-CdIn2Te4 heterojunctions could be
used for efficient substitution of the traditional silicon-
based photodiodes in the devices intended for applications
under extreme environment conditions.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2010. V. 13, N 4. P. 444-447.
© 2010, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
445
2. Research objects and methodology
The studied heterojunctions were formed on the base of
non-doped SnS2 and СdIn2Te4 single crystals, grown by
the modified Bridgman method from stoichiometric
melt. The samples of СdIn2Te4 and SnS2 displayed n-
type conductivity with the carrier concentration and
mobility (T = 300 K): 313cm10)91( n ,
sV/cm)140130( 2 n for СdIn2Te4 [8] and
315 cm10)31( n , sV/cm)9580( 2 n for
SnS2, respectively.
The substrates were made from 500-900 μm thick
monocrystalline plates of n-СdIn2Te4, subjected to
mechanical and chemical polishing with further careful
rinsing [9] to achieve the surface quality required for
construction of a heterojunction. n-SnS2 plates with the
area of several square millimeters were obtained by
chipping off the thin layers (~10 μm) from the
monocrystalline sample. The resulting plates had mirror-
smooth and perfect surfaces, making no additional
treatment required. The freshly-chipped n-SnS2 plates
were put on the top of n-СdIn2Te4 substrates and pressed
together, joining both materials into a strong optical
contact due to adhesion phenomena. Further, ohmic
contacts to heterojunction were created by fusion of
indium.
CVC of n-SnS2/n-CdIn2Te4 heterojunctions were
measured in DC mode under a forward bias; the
resulting curves featured pronounced rectifying
characteristics in all the temperature range studied (250-
332 K). The rectification coefficient, determined for
U = 1 V, was decreasing from 1600 down to 250 upon
device exposure to higher temperatures. The prepared
heterojunction exhibited a high quantum efficiency
within the energy range 1.3-2.1 eV. Upon illumination
from the n-SnS2 side (light source with a power
90 mW/cm2), open circuit voltage of 0.56 V was
reached.
3. Results and discussion
Our analysis of the temperature influence on the
heterojunction CVCs confirmed the possibility to
describe the properties of n-SnS2/n-CdIn2Te4 structure
using the model of a sharp heterojunction suggested by
Anderson [7, 10]. The obtained current-voltage plots
were typical for the isotype semiconductor
heterostructures. In particular, it was found that for the
voltages 0.95 V < U < 3.0 V one can describe the
current with a linear dependence:
)(~ 0UUCI , (1)
where U0 = (0.78±0.01) V is a cut-off voltage
determined by extrapolation of the linear CVC segments
(Fig. 1) to an intersection with the voltage axis.
It is important that for 0.95 V < U < 3.0 V the
temperature dependence of the current at a fixed voltage
(inset to Fig. 1) obeys the formula:
Fig. 1. Current-voltage characteristics for a forward-biased n-
SnS2/n-CdIn2Te4 heterojunction at the different temperatures.
The inset shows the current as a function of reverse
temperature at a fixed voltage.
kTEI a /exp~ , (2)
where Еа = (0.35±0.01) eV is the activation energy, which
reasonably correlates with Еа = (0.42±0.03) eV for the
intrinsic defects in CdIn2Te4 [8]. It is worth mentioning
that the activation energy for n-SnS2 defects, accordingly
to the paper [11] and references therein, is within the
range 0.20-0.26 eV. Thus, the obtained Ea value
confirms that the specific resistivity of heterojunction
investigated is determined by the resistance of CdIn2Te4
substrate, and its temperature dependence is caused by
the presence of an energy level formed by the intrinsic
defects in the band gap of the base semiconductor.
The detailed analysis of the influence caused by the
temperature on the CVC measured has shown that
forward-biased n-SnS2/n-CdIn2Te4 structure
(U < 0.75 V) is governed by two current transport
mechanisms: generation-recombination (Igr) and
tunneling (It) ones. However, it was found that in a
certain voltage intervals only one of these mechanisms is
dominating.
For the direct biases 0 V < U < 0.32 V, generation
and recombination of carriers significantly overcomes
tunneling, so CVC of the device can be successfully
described with the formula [7, 10]:
1ln
0
0
grI
I
e
Tk
nU . (3)
Here, n is the non-ideality coefficient.
)/()0(exp 0
0 TnkEI ggr . (4)
0
grI is a cut-off current determined at U 0 V for the
material with a bandgap Eg(0) at T 0 K, all other
designations are common.
Performing the calculations in accordance to (3) for
the different temperatures (Fig. 2), we determined the
value of non-ideality coefficient as n = 2.0±0.1. Plotting
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2010. V. 13, N 4. P. 444-447.
© 2010, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
446
the experimental dependence )(ln 0 TIgr (inset to Fig. 2)
allowed to find the activation energy Eg(0) =
(1.1±0.1) eV, which fits into the interval Eg(CdIn2Te4) =
(0.9÷1.24) eV usually mentioned in the literature (e.g.
the paper [12] and references therein). This result proves
that the most possible model for generation-
recombination processes in the heterojunction studied
involves carrier recombination over the slow
recombination centers, located at the boundary between
the semiconductors. Such centers could appear as a
consequence of misfit dislocations, caused by broken
bonds of both SnS2 and СdIn2Te4 due to a significant
mismatch of crystalline lattice parameters in the base
materials.
For the bias 0.35 V < U < 0.71 V, tunneling current
transport becomes significantly prevalent [7, 10], which
is confirmed by the semi-logarithmic scale plots of CVC
for n-SnS2/n-CdIn2Te4 heterojunction, yielding a set of
parallel segments (Fig. 3).
Fig. 2. Current-voltage plots for n-SnS2/n-CdIn2Te4
heterojunction in the case of dominating generation-
recombination transport. The inset shows the cut-off current
0
grI as a function of the reverse temperature.
Fig. 3. Current-voltage plots for n-SnS2/n-CdIn2Te4
heterojunctions for tunneling carrier transport. The inset
displays the cut-off current 0
tI as a function of the
temperature.
In this case, CVC can be successfully described
with the expression [7]:
)exp(0 TUII tt , (5)
where )exp(0
dt UBI is a cut-off current at U = 0,
Ud is a diffusion potential difference, В is a constant
determined by heterojunction parameters, α and β are the
parameters independent on voltage and temperature,
correspondingly. For the tunneling current, the tangent
of the slope found from the semi-logarithmic CVC plot
yields 1V19.26 . The dependence of cut-off current
0
tI on the temperature also reveals linear character upon
plotting in the semi-logarithmic scale (inset to Fig. 3),
displaying a slope 12 K1072.7 .
Our analysis (Fig. 4) suggests that for U > 0.75 V
current-voltage plots obeys well the following
expression [10], corresponding to over-barrier current:
TkC
Ie
I
Tk
Ue
I b
0
0
0
lnln , (6)
with the same constant C as that in formula (1) and cut-
off current Ib0 (for U = 0 V). The temperature
dependence of the latter is determined as [10]:
Tk
e
TAI b
b
0
2
0 exp . (7)
Here, eφb is the energetic barrier height; the value
A is determined by heterojunction model (effective
masses of the carriers, area of the contact, etc.) and is
usually chosen to be a fitting parameter. Curves
)()/(ln 0 IfTkeUI , plotted for the different
temperatures (Fig. 4), feature several straight segments.
Extrapolating the latter to the intersection with the
ordinate axis, we plotted experimental temperature
dependence of cut-off, which can be also brought to
straight-segment form upon using the coordinates
)/10(ln 3
0 TfIb (inset to Fig. 4).
Fig. 4. Current-voltage characteristics of a n-SnS2/n-CdIn2Te4
heterojunction for over-barrier current transport under different
temperatures. The inset shows the cut-off current Ib0(T).
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2010. V. 13, N 4. P. 444-447.
© 2010, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
447
The slope of the latter plots corresponds to the
height of a energetic barrier eφb = (0.85±0.02) eV of the
structure. It is worth mentioning that the obtained eφb for
n-SnS2/n-CdIn2Te4 heterojunction is higher than that for
n-InSe/p-СdTe (eφb = 0.71 eV) and n-InSe/p-GaSe
(eφb = 0.73 eV) [13, 14]. The latter suggests promising
perspectives for applications of n-SnS2/n-CdIn2Te4
heterojunction in IR-devices, intended for a stable
operation under the elevated temperatures and high
incident radiation.
4. Conclusions
Therefore, the results of a complex study of current
transport mechanisms taking place in isotype n-SnS2/n-
CdIn2Te4 heterojunction created by the deposition over
optical contact proves the significant advantages of this
structure and suggests its possible applications as an
analogue of n-InSe/p-CdTe and n-InSe/p-GaSe
heterojunctions. Investigations of temperature
dependences of current-voltage characteristics revealed
that n-SnS2/n-CdIn2Te4 junction is characterized by
several current transport mechanisms upon application
of a direct bias U < 0.95 V, including generation-
recombination, tunneling and over-barrier currents. All
three mechanisms were thoroughly studied, determining
the voltage ranges for which each of them becomes
predominating. On the base of the results obtained, it is
possible to predict good perspectives for n-SnS2/n-
CdIn2Te4 junction in the devices intended to operate
under high temperatures and radiation fluxes.
References
1. Z.M. Grushka, P.N. Gorley, O.G. Grushka,
P.P. Horley, Ya.I. Radevych, Zh. Zhuo, Mercury
indium telluride – a new promising material for
photonic structures and devices // Proc. SPIE,
6029, p. 60291A (2006).
2. C. Wang, K. Tang, Q. Yang, Y. Quan, Raman
scattering, far infrared spectrum and
photoluminescence of SnS2 nanocrystallites //
Chem. Phys. Lett., 357, p. 371-375 (2002).
3. G.B. Dubrovsky, Crystal structure and electron
spectrum of SnS2 // Fizika Tverdogo Tela 40,
p. 1712-1718 (1998), in Russian.
4. D.B. Ananina, V.L. Bakumenko, А.K. Bodnakov,
G.G. Grushka, About characteristics of n-SnS2/n-
Hg3In2Te6 heterojunction, prepared by a method of
deposition over optical contact // Fizika i Tekhnika
Poluprovodnikov, 14 (12), p. 2419-2422 (1980), in
Russian.
5. S. Ozaki, Y. Take, S. Adachi, Optical properties
and electronic energy-band structure of CdIn2Te4 //
J. Mater. Sci.: Mater. Electron., 18, p. S347-S350
(2007).
6. L.P. Galchinetskyy, V.M. Koshkin, V.М. Kumakov
et al., Effect of radiating stability of semiconduc-
tors with stoichiometric vacancies // Fizika Tver-
dogo Tela 14 (2), p. 643-646 (1972), in Russian.
7. S.M. Sze, Physics of Semiconductor Devices. Mir,
Moscow (1984), in Russian.
8. P.M. Gorley, O.G. Grushka, O.I. Vorobets,
Z.M. Grushka, Temperature dependences of the
concentration of carriers in CdIn2Te4 crystals //
Ukr. J. Phys. 51(5), p. 475-477 (2006).
9. Ya.S. Mazurkevych, A.G. Voloshchuk,
S.B. Kostenko, G.G. Grushka, Method of chemical
surface treatment of the tellurium-containing
semiconductor materials, Patent №1080680 (1983).
10. B.L. Sharma, P.K. Purohit, Semiconductor
Heterojunction, Mir, Moscow (1979), in Russian.
11. L. Amalraj, C. Sanjeeviraja, M. Jayachandran, Spray
pyrolysised tin disulphide thin film and character-
rization // J. Cryst. Growth, 234, p. 683-689 (2002).
12. J.-F. Lambert, Cristallogenèse et caractérisations
physico-chimiques et optiques des matériaux semi-
conducteurs AIn2Te4 (A = Cd, Zn et Mn). Leurs
potentialités comme modulateurs dans la bande
spectrale 1,06-10,6 micromètres, PhD These
(1993), in French.
13. P.M. Gorley, I.V. Prokopenko, Z.M. Grushka,
V.P. Makhniy, O.G. Grushka, O.A. Chervinsky,
Direct current transport mechanisms in n-InSe/p-
CdTe heterostructure // Semiconductor Physics,
Quantum Electronics & Optoelectronics 11 (2),
p. 124-131 (2008).
14. P.M. Gorley, Z.M. Grushka, V.P. Makhniy,
O.G. Grushka, O.A. Chervinsky, P.P. Horley,
Yu.V. Vorobiev, J. Gonzalez-Hernandez, Сurrent
transport mechanisms in n-InSe/p-CdTe
heterojunctions // Phis. status solidi (c), 5(12),
p. 3622-3625 (2008).
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2010. V. 13, N 4. P. 444-447.
PACS 73.40.Cg, Gk, Lq
Electrical properties of n-SnS2/n-CdIn2Te4 heterostructure
P.M. Gorley1, Z.M. Grushka1, O.G. Grushka1, P.P. Gorley1,2, I.I. Zabolotsky1
1Yu. Fedkovych Chernivtsi National University,
2, Kotsyubynsky str., 58012 Chernivtsi, Ukraine,
Phone: +38 03722 46877, fax: +38 03722 46877,
E-mail: semicon-dpt@chnu.edu.ua
2Centro de Física das Interacções Fundamentais,
Av. Rovisco Pais, 1049-001 Lisboan, Portugal
Phone: +351 21 8419690, e-mail: pphorley@cfif.ist.utl.pt
Abstract. Using the method of deposition over the optical contact, the authors created n-SnS2/n-CdIn2Te4 heterojunction and investigated temperature evolution of its current-voltage characteristics under the forward bias U ≤ 3 V. Analyzing temperature dependence of the curves obtained, the main mechanisms of current transport through the semiconductor contact were determined, allowing prediction of successful possible applications of the heterojunction studied under high temperatures and elevated radiation due to the parameters of the base semiconductors and the diode structure itself.
Keywords: heterojunction, n-SnS2/n-CdIn2Te4, optical contact, current-voltage curve, current transport mechanisms.
Manuscript received 30.12.09; accepted for publication 02.12.10; published online 30.12.10.
1. Introduction
At the modern development stage of electronics, it is especially timely and important task to create devices able to operate under the significant fluxes of ionizing radiation, and also at the elevated temperatures without additional cooling. Among these devices, one should mention rectifying structures based on layered semiconductors and materials with the stoichiometric vacancies (see, e.g., paper [1] and references therein). This is caused by the fact that layered semiconductors (including SnS2) possess many unique physical and chemical properties [2]. In particular, predominant Van-der-Waals binding between the layers allows the possibility to obtain thin and quite elastic plates with mirror-smooth and practically ideal surface [2, 3] by simple material chipping from the monocrystalline ingots. Another technologically-important detail concerns the ability to create heterojunction to the layered semiconductors by deposition over the optical contact. This method does not require high-temperature treatment and yields good adhesion of the junction components, approaching bulk durability of the contacting materials [4].
The beneficial peculiarities of materials with the so-called defect semiconductor phases (including Hg3In2Te6 and CdIn2Te4) is the large concentration of stoichiometric vacancies (up to ~
3
21
cm
10
-
[5]), which causes high semiconductor stability towards the action of ionizing radiation [1, 6]. The latter phenomenon attracts significant interest to the defect phases as promising materials for creation of the photosensitive structures, able to operate under high temperatures without any additional cooling.
This paper presents the results concerning technology for n-SnS2/n-CdIn2Te4 heterojunctions using the methodology of deposition over optical contact, as well as the detailed study of their current-voltage characteristics (CVC) under the forward bias. Using the Anderson model [7] for the sharp heterojunction, we have estimated the height of the potential barrier within heterostructure, determined the dominating current transport mechanisms of transformation between them upon application of a different voltage. The obtained results allowed to conclude that n-SnS2/n-CdIn2Te4 heterojunctions could be used for efficient substitution of the traditional silicon-based photodiodes in the devices intended for applications under extreme environment conditions.
2. Research objects and methodology
The studied heterojunctions were formed on the base of non-doped SnS2 and СdIn2Te4 single crystals, grown by the modified Bridgman method from stoichiometric melt. The samples of СdIn2Te4 and SnS2 displayed n-type conductivity with the carrier concentration and mobility (T = 300 K):
3
13
cm
10
)
9
1
(
-
´
¸
»
n
,
(
)
s
V
/
cm
)
140
130
(
2
×
¸
»
m
n
for СdIn2Te4 [8] and
3
15
cm
10
)
3
1
(
-
´
¸
»
n
,
(
)
s
V
/
cm
)
95
80
(
2
×
¸
»
m
n
for SnS2, respectively.
The substrates were made from 500-900 μm thick monocrystalline plates of n-СdIn2Te4, subjected to mechanical and chemical polishing with further careful rinsing [9] to achieve the surface quality required for construction of a heterojunction. n-SnS2 plates with the area of several square millimeters were obtained by chipping off the thin layers (~10 μm) from the monocrystalline sample. The resulting plates had mirror-smooth and perfect surfaces, making no additional treatment required. The freshly-chipped n-SnS2 plates were put on the top of n-СdIn2Te4 substrates and pressed together, joining both materials into a strong optical contact due to adhesion phenomena. Further, ohmic contacts to heterojunction were created by fusion of indium.
CVC of n-SnS2/n-CdIn2Te4 heterojunctions were measured in DC mode under a forward bias; the resulting curves featured pronounced rectifying characteristics in all the temperature range studied (250-332 K). The rectification coefficient, determined for U = 1 V, was decreasing from 1600 down to 250 upon device exposure to higher temperatures. The prepared heterojunction exhibited a high quantum efficiency within the energy range 1.3-2.1 eV. Upon illumination from the n-SnS2 side (light source with a power 90 mW/cm2), open circuit voltage of 0.56 V was reached.
3. Results and discussion
Our analysis of the temperature influence on the heterojunction CVCs confirmed the possibility to describe the properties of n-SnS2/n-CdIn2Te4 structure using the model of a sharp heterojunction suggested by Anderson [7, 10]. The obtained current-voltage plots were typical for the isotype semiconductor heterostructures. In particular, it was found that for the voltages 0.95 V < U < 3.0 V one can describe the current with a linear dependence:
)
(
~
0
U
U
C
I
-
×
,
(1)
where U0 = (0.78±0.01) V is a cut-off voltage determined by extrapolation of the linear CVC segments (Fig. 1) to an intersection with the voltage axis.
It is important that for 0.95 V < U < 3.0 V the temperature dependence of the current at a fixed voltage (inset to Fig. 1) obeys the formula:
Fig. 1. Current-voltage characteristics for a forward-biased n-SnS2/n-CdIn2Te4 heterojunction at the different temperatures. The inset shows the current as a function of reverse temperature at a fixed voltage.
(
)
kT
E
I
a
/
exp
~
-
,
(2)
where Еа = (0.35±0.01) eV is the activation energy, which reasonably correlates with Еа = (0.42±0.03) eV for the intrinsic defects in CdIn2Te4 [8]. It is worth mentioning that the activation energy for n-SnS2 defects, accordingly to the paper [11] and references therein, is within the range 0.20-0.26 eV. Thus, the obtained Ea value confirms that the specific resistivity of heterojunction investigated is determined by the resistance of CdIn2Te4 substrate, and its temperature dependence is caused by the presence of an energy level formed by the intrinsic defects in the band gap of the base semiconductor.
The detailed analysis of the influence caused by the temperature on the CVC measured has shown that forward-biased n-SnS2/n-CdIn2Te4 structure (U < 0.75 V) is governed by two current transport mechanisms: generation-recombination (Igr) and tunneling (It) ones. However, it was found that in a certain voltage intervals only one of these mechanisms is dominating.
For the direct biases 0 V < U < 0.32 V, generation and recombination of carriers significantly overcomes tunneling, so CVC of the device can be successfully described with the formula [7, 10]:
÷
÷
ø
ö
ç
ç
è
æ
+
=
1
ln
0
0
gr
I
I
e
T
k
n
U
.
(3)
Here, n is the non-ideality coefficient.
(
)
)
/(
)
0
(
exp
0
0
T
nk
E
I
g
gr
-
»
.
(4)
0
gr
I
is a cut-off current determined at U ( 0 V for the material with a bandgap Eg(0) at T ( 0 K, all other designations are common.
Performing the calculations in accordance to (3) for the different temperatures (Fig. 2), we determined the value of non-ideality coefficient as n = 2.0±0.1. Plotting the experimental dependence
)
(
ln
0
T
I
gr
(inset to Fig. 2) allowed to find the activation energy Eg(0) = (1.1±0.1) eV, which fits into the interval Eg(CdIn2Te4) = (0.9÷1.24) eV usually mentioned in the literature (e.g. the paper [12] and references therein). This result proves that the most possible model for generation-recombination processes in the heterojunction studied involves carrier recombination over the slow recombination centers, located at the boundary between the semiconductors. Such centers could appear as a consequence of misfit dislocations, caused by broken bonds of both SnS2 and СdIn2Te4 due to a significant mismatch of crystalline lattice parameters in the base materials.
For the bias 0.35 V < U < 0.71 V, tunneling current transport becomes significantly prevalent [7, 10], which is confirmed by the semi-logarithmic scale plots of CVC for n-SnS2/n-CdIn2Te4 heterojunction, yielding a set of parallel segments (Fig. 3).
Fig. 2. Current-voltage plots for n-SnS2/n-CdIn2Te4 heterojunction in the case of dominating generation-recombination transport. The inset shows the cut-off current
0
gr
I
as a function of the reverse temperature.
Fig. 3. Current-voltage plots for n-SnS2/n-CdIn2Te4 heterojunctions for tunneling carrier transport. The inset displays the cut-off current
0
t
I
as a function of the temperature.
In this case, CVC can be successfully described with the expression [7]:
)
exp(
0
T
U
I
I
t
t
b
+
a
×
=
,
(5)
where
)
exp(
0
d
t
U
B
I
a
-
×
=
is a cut-off current at U = 0, Ud is a diffusion potential difference, В is a constant determined by heterojunction parameters, α and β are the parameters independent on voltage and temperature, correspondingly. For the tunneling current, the tangent of the slope found from the semi-logarithmic CVC plot yields
1
V
19
.
26
-
=
a
. The dependence of cut-off current
0
t
I
on the temperature also reveals linear character upon plotting in the semi-logarithmic scale (inset to Fig. 3), displaying a slope
1
2
K
10
72
.
7
-
-
×
=
b
.
Our analysis (Fig. 4) suggests that for U > 0.75 V current-voltage plots obeys well the following expression [10], corresponding to over-barrier current:
T
k
C
I
e
I
T
k
U
e
I
b
0
0
0
ln
ln
-
=
-
,
(6)
with the same constant C as that in formula (1) and cut-off current Ib0 (for U = 0 V). The temperature dependence of the latter is determined as [10]:
÷
÷
ø
ö
ç
ç
è
æ
j
-
×
×
=
T
k
e
T
A
I
b
b
0
2
0
exp
.
(7)
Here, eφb is the energetic barrier height; the value A is determined by heterojunction model (effective masses of the carriers, area of the contact, etc.) and is usually chosen to be a fitting parameter. Curves
)
(
)
/(
ln
0
I
f
T
k
eU
I
=
-
, plotted for the different temperatures (Fig. 4), feature several straight segments. Extrapolating the latter to the intersection with the ordinate axis, we plotted experimental temperature dependence of cut-off, which can be also brought to straight-segment form upon using the coordinates
)
/
10
(
ln
3
0
T
f
I
b
=
(inset to Fig. 4).
Fig. 4. Current-voltage characteristics of a n-SnS2/n-CdIn2Te4 heterojunction for over-barrier current transport under different temperatures. The inset shows the cut-off current Ib0(T).
The slope of the latter plots corresponds to the height of a energetic barrier eφb = (0.85±0.02) eV of the structure. It is worth mentioning that the obtained eφb for n-SnS2/n-CdIn2Te4 heterojunction is higher than that for n-InSe/p-СdTe (eφb = 0.71 eV) and n-InSe/p-GaSe (eφb = 0.73 eV) [13, 14]. The latter suggests promising perspectives for applications of n-SnS2/n-CdIn2Te4 heterojunction in IR-devices, intended for a stable operation under the elevated temperatures and high incident radiation.
4. Conclusions
Therefore, the results of a complex study of current transport mechanisms taking place in isotype n-SnS2/n-CdIn2Te4 heterojunction created by the deposition over optical contact proves the significant advantages of this structure and suggests its possible applications as an analogue of n-InSe/p-CdTe and n-InSe/p-GaSe heterojunctions. Investigations of temperature dependences of current-voltage characteristics revealed that n-SnS2/n-CdIn2Te4 junction is characterized by several current transport mechanisms upon application of a direct bias U < 0.95 V, including generation-recombination, tunneling and over-barrier currents. All three mechanisms were thoroughly studied, determining the voltage ranges for which each of them becomes predominating. On the base of the results obtained, it is possible to predict good perspectives for n-SnS2/n-CdIn2Te4 junction in the devices intended to operate under high temperatures and radiation fluxes.
References
1. Z.M. Grushka, P.N. Gorley, O.G. Grushka, P.P. Horley, Ya.I. Radevych, Zh. Zhuo, Mercury indium telluride – a new promising material for photonic structures and devices // Proc. SPIE, 6029, p. 60291A (2006).
2. C. Wang, K. Tang, Q. Yang, Y. Quan, Raman scattering, far infrared spectrum and photoluminescence of SnS2 nanocrystallites // Chem. Phys. Lett., 357, p. 371-375 (2002).
3. G.B. Dubrovsky, Crystal structure and electron spectrum of SnS2 // Fizika Tverdogo Tela 40, p. 1712-1718 (1998), in Russian.
4.
D.B. Ananina, V.L. Bakumenko, А.K. Bodnakov, G.G. Grushka, About characteristics of n-SnS2/n-Hg3In2Te6 heterojunction, prepared by a method of deposition over optical contact // Fizika i Tekhnika Poluprovodnikov, 14 (12), p. 2419-2422 (1980), in Russian.
5. S. Ozaki, Y. Take, S. Adachi, Optical properties and electronic energy-band structure of CdIn2Te4 // J. Mater. Sci.: Mater. Electron., 18, p. S347-S350 (2007).
6. L.P. Galchinetskyy, V.M. Koshkin, V.М. Kumakov et al., Effect of radiating stability of semiconductors with stoichiometric vacancies // Fizika Tverdogo Tela 14 (2), p. 643-646 (1972), in Russian.
7. S.M. Sze, Physics of Semiconductor Devices. Mir, Moscow (1984), in Russian.
8. P.M. Gorley, O.G. Grushka, O.I. Vorobets, Z.M. Grushka, Temperature dependences of the concentration of carriers in CdIn2Te4 crystals // Ukr. J. Phys. 51(5), p. 475-477 (2006).
9. Ya.S. Mazurkevych, A.G. Voloshchuk, S.B. Kostenko, G.G. Grushka, Method of chemical surface treatment of the tellurium-containing semiconductor materials, Patent №1080680 (1983).
10. B.L. Sharma, P.K. Purohit, Semiconductor Heterojunction, Mir, Moscow (1979), in Russian.
11. L. Amalraj, C. Sanjeeviraja, M. Jayachandran, Spray pyrolysised tin disulphide thin film and characterrization // J. Cryst. Growth, 234, p. 683-689 (2002).
12. J.-F. Lambert, Cristallogenèse et caractérisations physico-chimiques et optiques des matériaux semi-conducteurs AIn2Te4 (A = Cd, Zn et Mn). Leurs potentialités comme modulateurs dans la bande spectrale 1,06-10,6 micromètres, PhD These (1993), in French.
13. P.M. Gorley, I.V. Prokopenko, Z.M. Grushka, V.P. Makhniy, O.G. Grushka, O.A. Chervinsky, Direct current transport mechanisms in n-InSe/p-CdTe heterostructure // Semiconductor Physics, Quantum Electronics & Optoelectronics 11 (2), p. 124-131 (2008).
14. P.M. Gorley, Z.M. Grushka, V.P. Makhniy, O.G. Grushka, O.A. Chervinsky, P.P. Horley, Yu.V. Vorobiev, J. Gonzalez-Hernandez, Сurrent transport mechanisms in n-InSe/p-CdTe heterojunctions // Phis. status solidi (c), 5(12), p. 3622-3625 (2008).
© 2010, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
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