Electrical Properties of CdFeSe, CdMnTe Epitaxial Films
1MEHRABOVA M. A., 2HASANOV N.H., 3GULUZADE V.G., 4SADIGOV R.M.
1Institute of Radiation Problems, Azerbaijan National Academy of Sciences,
1143, B.Vahabzade, 9, Baku, AZERBAIJAN
2Baku State University, 1148, Z.Khalilov, 23, Baku, AZERBAIJAN
3Azerbaijan Technical University, 1073, H. Javid ave. 25, Baku, AZERBAIJAN
2Institute of Physics, Azerbaijan National Academy of Sciences,
1143, H.Javid ave. 131, Baku, AZERBAIJAN
Abstract: - Optimal conditions of obtaining perfect Cd1–xFexSe (x<0.08) and Cd1-xMnxTe (x=0.15) epitaxial
films are defined. The electrical properties of Cd1–xFexSe (x<0.08) and Cd1-xMnxTe (x=0.15) epitaxial films
have been studied at room temperature. It was defined that Cd1–xFexSe semimagnetic semiconductor epitaxial
films are of n-type and Cd1-xMnxTe p-type. Electrical resistivity was defined 14.4 ·107 Ohm⋅cm. The effect of
γ-irradiation on VAC of Cd1-xMnxTe epitaxial films is studied at doses Dγ ≤ 1.5 кGy.
Key-Words: - Semimagnetic semiconductors, molecular beam condensation, XRD, SEM, electrical, VAC
Received: April 18, 2021. Revised: April 12, 2022. Accepted: May 5, 2022. Published: June 6, 2022.
1 Introduction
Semimagnetic semiconductors (SMSC) are of II-VI
and IV-VI group compounds in which a fraction of
nonmagnetic cations has been substituted by
magnetic transition metal ions. Most of the research
performed so far on these materials has been
devoted to Mn-based SMSC, which represents a
rather simple magnetic case, since the Mn+2
ions possess only spin momentum (S = 5/2, L = 0)
[1], [2], [3], [4].
A natural development of SMSC is
growing crystals with other transition metals, in
particular, with Fe+2. Materials based on Fe are
not a simple extension of the SMSC family,
since the physical situation, in this case, differs
completely from that of Mn: substitutional Fe+2
possesses both spin and orbital momenta (S = 2, L
= 2). The problem of the Fe+2 dopant in II-VI
compounds has been studied for a long time. Unlike
the well-known Mn-based DMS [5], the Fe-based
II-VI compounds show a very low solubility of
Fe, creating some difficulties in obtaining
single - phase samples for studying the electronic
properties. The Cd1–xFexSe DMS are single-
phase for x < 0.15. In Cd1–xFexSe the
transition metal Fe2+ ions replace randomly the
Cd cations in the wurtzite structure of the host
CdSe crystal [2]. Similarly to the Mn-based DMS's
[6], [7], there is a large exchange interaction
between the Fe 3d electrons, which leads to the spin
splitting of the Fe 3d states into two groups of
sublevels (spin-up and spin-down). In this work
the conditions of obtaining perfect Cd1-xFexSe (x
< 0.08) and Cd1-xMnxTe (x = 0.15) epitaxial films
and study of their electrical properties have been
studied.
2 Experimental
Thin films of Cd1-xFexSe (x < 0.08) and Cd1-xMnxTe
(x=0.15) epitaxial films were obtained by the
Molecular Beam Condensation method in a vacuum
of (1÷2)10-4 Pа on glass substrates. It is determined
the optimal conditions to obtain epitaxial films with
perfect structure and a clean, smooth surface. The
substrate temperature was Tsub=640 ÷ 670К and
source temperature was Tsub = 1100 ÷1200К.
Epitaxial films were growing in the (111) plane of a
face-centered cubic lattice.
Crystal structure of investigated epitaxial
films was studied by X-ray diffraction (XRD)
method on Bruker, Germany D8 ADVANGE X-ray
diffractometer. XRD studies show that thin films
grown on glass substrates at temperature Tsub = 640
÷670 К have a monocrystalline (fig.1,a) and
polycrystalline (fig.1,b) structures. To characterize a
film quality, the full width at half maximum
(FWHM) of diffraction peak is used. The FWHM of
diffraction peak for Cd1-xFexSe (x = 0.04) is W1/2 =
1000-1100” (fig.1,a, insertion) and for Cd1-xMnxTe
(x = 0.15) is W1/2 = 1000-1100” (fig.1,b, insertion).
WSEAS TRANSACTIONS on ELECTRONICS
DOI: 10.37394/232017.2022.13.4
Mehrabova M. A., Hasanov N. H.,
Guluzade V. G., Sadigov R. M.
E-ISSN: 2415-1513
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a)
b)
Fig. 1. X-ray diffraction pattern of a) Cd1-xFexSe (x
= 0.04), b) Cd1-xMnxTe (x = 0.15)
The surface morphology of investigated epitaxial
films was studied by Scanning Electron Microscope
(SEM) method on JEOL JSM-7600F Field Emission
SEM (fig. 2). SEM image shows that the obtained
Cd1-xFexSe epitaxial films were smooth and glossy
(fig.2,a), but surface of Cd1-xMnxTe epitaxial films
were roughness with a grain size of up to 10
microns (fig. 2,b).
a)
b)
Fig. 2. SEM image of the a) Cd1-xFexSe (x = 0.04)
b) Cd1-xMnxTe (x = 0.15) epitaxial films obtained
on the glass substrate
3 Results and Discussion
The dark electrical resistivity of Cd1-xFexSe, x < 0.08
epitaxial films was measured at T = 300 K
temperature. To measure electrical resistivity silver
paste was applied to make Ohmic contacts to
Cd1-xFexSe, x < 0.08 epitaxial films. The nature of
contact was checked up to 50 V. The VAC of
Cd1-xFexSe, x < 0.08 epitaxial films are shown in fig.
3. The VAC has linear nature which confirms that
silver produces Ohmic contact with Cd1-xFexSe. The
measurement of thermo–emf across Cd1-xFexSe
SMSC epitaxial films confirms that films are of n–
type.
Fig. 3. VAC of Cd1-xFexSe epitaxial films: 1- CdSe,
2- Cd0.6Fe0.4Se, 3- Cd0.2Fe0.8Se, 4-FeSe
VAC of Cd1-xMnxTe (x = 0.15) epitaxial films
has been studied at room temperature. There is
observed a linear part J ~ U corresponding to Ohm’s
law and quadratic part J ~ U2 in VAC (fig. 4). Cd1-
xMnxTe epitaxial films had p-type conductivity with
a resistivity of ρ=14.4 ·107 Ohm⋅cm.
The effect of γ-irradiation on VAC of
Cd1-xMnxTe epitaxial films is studied at T=300K at
doses Dγ ≤ 1.5 кGy. After irradiation of samples
WSEAS TRANSACTIONS on ELECTRONICS
DOI: 10.37394/232017.2022.13.4
Mehrabova M. A., Hasanov N. H.,
Guluzade V. G., Sadigov R. M.
E-ISSN: 2415-1513
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Volume 13, 2022
with γ- quanta at a dose of Dγ < 100 Gy, a parallel
shift of the curve occurs towards the current
decrease in the entire investigated voltage range
(fig. 4). The nature of dependence does not change,
Ohmic and quadratic parts are observed, the Ohmic
part lengthens. The observed character shows that at
irradiation of Cd1-xMnxTe thin films with small
doses, deep levels are formed in the band gap and
are captured by electrons, that leads to a decrease in
the conductivity. According to [8], when the sample
contains traps with the concentration exceeding the
concentration of majority carriers, the carriers
injected first are captured by the traps, and the
carrier concentration in the conduction band is
almost unchanged [9]. At irradiation of samples at
Dγ = 500 Gy dose Ohmic part in VAC decreases,
quadratic part lengthens, the conductivity increases.
Such a behavior of VAC can likely be due to the
thermal-field ionization of the traps [10] whose
concentration is dependent on the irradiation doze.
Further irradiation at doses Dγ ≥ 1.5 kGy leads to
increasing of Ohmic part and decreasing of
quadratic part, so conductivity decreases.
Significant decreasing of conductivity is explained
by increasing of defects concentration and so
destruction of the crystal structure. Obtained results
satisfy to the results of our previous works [9].
Fig. 4. VAC of irradiated Cd1-xMnxTe (x = 0.15)
epitaxial films: 1) Dγ = 0, 2) Dγ = 100 Gy, 3)Dγ =
500 Gy, 4)Dγ=1.5 кGy
4 Conclusion
Optimal conditions of obtaining perfect Cd1-xFexSe
(x < 0.08) and Cd1-xMnxTe (x = 0.15) epitaxial films
are defined. Crystal structure and surface
morphology have been investigated by XRD and
SEM methods. XRD studies show that thin films
grown on glass substrates at temperature Tsub = 640
÷670 К have a monocrystalline and polycrystalline
structures. SEM image shows that the obtained Cd1-
xFexSe epitaxial films were smooth and glossy, but
surface of Cd1-xMnxTe epitaxial films were
roughness with a grain size of up to 10 microns.
The electrical properties of Cd1-xFexSe (x < 0.08)
and Cd1-xMnxTe (x = 0.15) epitaxial films have been
studied at room temperature. It was defined that Cd1-
xFexSe SMSC epitaxial films are of n–type and Cd1-
xMnxTe SMSC epitaxial films are of p–type. It was
defined the electrical resistivity 14.4 ·107 Ohm⋅cm.
The effect of γ-irradiation on VAC of Cd1-xMnxTe
epitaxial films is studied at doses Dγ ≤ 1.5 кGy.
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WSEAS TRANSACTIONS on ELECTRONICS
DOI: 10.37394/232017.2022.13.4
Mehrabova M. A., Hasanov N. H.,
Guluzade V. G., Sadigov R. M.
E-ISSN: 2415-1513
25
Volume 13, 2022
Contribution of individual authors to
the creation of a scientific article
(ghostwriting policy)
Matanat Mehrabova was responsible for the
experimental work of electrical properties.
Niyazi Hasanov carried out the XRD and SEM
investigations
Vafa Guluzade has executed the experiments of
Section 3.
Rafig Sadigov obtained thin films.
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DOI: 10.37394/232017.2022.13.4
Mehrabova M. A., Hasanov N. H.,
Guluzade V. G., Sadigov R. M.
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Conflicts of Interest
The author(s) declare no potential conflicts
of interest concerning the research,
authorship, or publication of this article.
Sources of funding for research
presented in a scientific article
or scientific article itself
No funding was received for conducting
this study.
