Influence of Cr doping on optical and photoluminescent properties of CdTe
Spectra of transmission and low-temperature photoluminescence of CdTe:Cr crystals have been investigated for concentrations of the doping impurity (Cr) from 1∙10¹⁷ to 4∙10¹⁹ cm⁻³ in the melt. We have found additional absorption bands with maxima at λ₁ = 1.9 μm and λ2 = 7.0 μm induced by the pr...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2010
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irk-123456789-1178072017-05-27T03:06:24Z Influence of Cr doping on optical and photoluminescent properties of CdTe Ilashchuk, М.I. Parfenyuk, O.A. Ulyanytskiy, K.S. Brus, V.V. Vakhnyak, N.D. Spectra of transmission and low-temperature photoluminescence of CdTe:Cr crystals have been investigated for concentrations of the doping impurity (Cr) from 1∙10¹⁷ to 4∙10¹⁹ cm⁻³ in the melt. We have found additional absorption bands with maxima at λ₁ = 1.9 μm and λ2 = 7.0 μm induced by the presence of this dopant. An additional band of radiative recombination in the vicinity of 1.22 eV is caused by electron transitions from the conduction band to the deep donor levels Ev+(0.36-0.38) eV, which correspond to the Cr¹⁺ defect entering to clusters. We have also observed the shift of CdTe:Cr absorption edge to the longwave region. This shift is caused by strong lattice deformation near the Cr²⁺ impurity position due to the static Jahn-Teller effect. 2010 Article Influence of Cr doping on optical and photoluminescent properties of CdTe / М.I. Ilashchuk, O.A. Parfenyuk, K.S. Ulyanytskiy, V.V. Brus, N.D. Vakhnyak // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2010. — Т. 13, № 1. — С. P. 91-94 — Бібліогр.: 13 назв. — англ. 1560-8034 PACS 71.55.Gs, 78.20.Ci, 78.55.Et http://dspace.nbuv.gov.ua/handle/123456789/117807 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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English |
| description |
Spectra of transmission and low-temperature photoluminescence of CdTe:Cr
crystals have been investigated for concentrations of the doping impurity (Cr) from
1∙10¹⁷ to 4∙10¹⁹ cm⁻³ in the melt. We have found additional absorption bands with
maxima at λ₁ = 1.9 μm and λ2 = 7.0 μm induced by the presence of this dopant. An
additional band of radiative recombination in the vicinity of 1.22 eV is caused by
electron transitions from the conduction band to the deep donor levels Ev+(0.36-0.38) eV,
which correspond to the Cr¹⁺ defect entering to clusters. We have also observed the shift
of CdTe:Cr absorption edge to the longwave region. This shift is caused by strong lattice
deformation near the Cr²⁺ impurity position due to the static Jahn-Teller effect. |
| format |
Article |
| author |
Ilashchuk, М.I. Parfenyuk, O.A. Ulyanytskiy, K.S. Brus, V.V. Vakhnyak, N.D. |
| spellingShingle |
Ilashchuk, М.I. Parfenyuk, O.A. Ulyanytskiy, K.S. Brus, V.V. Vakhnyak, N.D. Influence of Cr doping on optical and photoluminescent properties of CdTe Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Ilashchuk, М.I. Parfenyuk, O.A. Ulyanytskiy, K.S. Brus, V.V. Vakhnyak, N.D. |
| author_sort |
Ilashchuk, М.I. |
| title |
Influence of Cr doping on optical and photoluminescent properties of CdTe |
| title_short |
Influence of Cr doping on optical and photoluminescent properties of CdTe |
| title_full |
Influence of Cr doping on optical and photoluminescent properties of CdTe |
| title_fullStr |
Influence of Cr doping on optical and photoluminescent properties of CdTe |
| title_full_unstemmed |
Influence of Cr doping on optical and photoluminescent properties of CdTe |
| title_sort |
influence of cr doping on optical and photoluminescent properties of cdte |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| publishDate |
2010 |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/117807 |
| citation_txt |
Influence of Cr doping on optical and photoluminescent properties of CdTe / М.I. Ilashchuk, O.A. Parfenyuk, K.S. Ulyanytskiy, V.V. Brus, N.D. Vakhnyak // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2010. — Т. 13, № 1. — С. P. 91-94 — Бібліогр.: 13 назв. — англ. |
| series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
| work_keys_str_mv |
AT ilashchukmi influenceofcrdopingonopticalandphotoluminescentpropertiesofcdte AT parfenyukoa influenceofcrdopingonopticalandphotoluminescentpropertiesofcdte AT ulyanytskiyks influenceofcrdopingonopticalandphotoluminescentpropertiesofcdte AT brusvv influenceofcrdopingonopticalandphotoluminescentpropertiesofcdte AT vakhnyaknd influenceofcrdopingonopticalandphotoluminescentpropertiesofcdte |
| first_indexed |
2025-07-08T12:49:54Z |
| last_indexed |
2025-07-08T12:49:54Z |
| _version_ |
1837083126824697856 |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2010. V. 13, N 1. P. 91-94.
© 2010, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
91
PACS 71.55.Gs, 78.20.Ci, 78.55.Et
Influence of Cr doping on optical
and photoluminescent properties of CdTe
М.I. Ilashchuk1, O.A. Parfenyuk1, K.S. Ulyanytskiy1, V.V. Brus1, N.D. Vakhnyak2
1Yuri Fedkovych Chernivtsi National University,
2, Kotsyubynsky str., 58012 Chernivtsi, Ukraine,
Phone: +38 (03722) 46-877, fax: +38 (03722) 46-877; e-mail: semicon@chnu.cv.ua
2V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine,
41, prospect Nauky, 03028 Kyiv, Ukraine; e-mail: div47@isp.kiev.ua
Abstract. Spectra of transmission and low-temperature photoluminescence of CdTe:Cr
crystals have been investigated for concentrations of the doping impurity (Cr) from
1∙1017 to 4∙1019 cm-3 in the melt. We have found additional absorption bands with
maxima at 1 1.9 μm and 2 7.0 μm induced by the presence of this dopant. An
additional band of radiative recombination in the vicinity of 1.22 eV is caused by
electron transitions from the conduction band to the deep donor levels Ev+(0.36-0.38) eV,
which correspond to the Cr1+ defect entering to clusters. We have also observed the shift
of CdTe:Cr absorption edge to the longwave region. This shift is caused by strong lattice
deformation near the Cr2+ impurity position due to the static Jahn-Teller effect.
Keywords: CdTe, magnetic dopant, intra-center transitions, photoluminescence, trans-
mission spectra.
Manuscript received 12.10.09; accepted for publication 22.10.09; published online 30.12.09.
1. Introduction
CdTe crystals doped with Cr atoms are a promising
material for highly efficient lasers in the middle infrared
spectral range [1] as well as a magnetic semiconductor
for spintronic applications [2]. Further practical
applications of this material depend on understanding
the Cr impurity behaviour in CdTe crystal lattice and the
mentioned dopant influence on the electrical, optical and
magnetic properties. Investigation of these problems is
essentially complicated by interaction of localized
magnetic moments of electrons on the unoccupied 3d-
shell between each others and the crystal band electrons.
The latter causes splitting the magnetic impurity energy
levels, if the impurity is localized in the initial material
lattice sites. Transitions between splitted levels and
allowed energy bands essentially complicate the
experimental data analysis.
The objective of this work was to investigate the
influence of technological factors (dopant concentration,
location of samples along the ingot length) on CdTe:Cr
optical and photoluminescenсe spectra.
2. Investigated objects and methodology
The studied CdTe:Cr crystals were grown using the
Bridgmen method at low Cd vapour pressure in the
ampoule (PCd 0.02 atm) with the purity of initial
materials: Cd (99.9999 %) and Te (99.99999 %). The
impurity (Cr) concentration in the melt was between
С0 = 31917 cm1010 . The obtained material had p-
type conductivity and specific resistance = (105-
106) Ohm∙cm.
The samples for the measurements of transmission
spectra were prepared from the different parts of the
ingot with the Cr concentration С0 = 319 cm10 . The
photoluminescence spectra measurements at low
temperature (4.2 K) were performed on freshly cleaved
surfaces of the samples taken from the middle part of the
ingots with various Cr concentrations.
The measurements of CdTe transmission spectra in
the absorption edge region ( = 0.8-2.2 μm) were carried
out by means of МДР-23 monochromator. The infrared
spectrophotometer ИКС-29 was used for measurements
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2010. V. 13, N 1. P. 91-94.
© 2010, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
92
of transmission spectra within the infrared range 2.0 to
25 μm.
The photoluminescence spectra were investigated
by the standard procedure employing the facility based
on МДР-23 monochromator. The 40 mW power He-Ne
laser was used for excitation. The spectral range of
investigations was 7700 to 9300 Å.
3. Results and discussion
Transmission spectra. The spectral dependences of
transmission coefficient for the CdTe:Cr crystals in the
range of the absorption edge and in the transparent
region are shown in Fig. 1a,b.
The obtained spectra analysis allowed us to
determine the peculiarities related to doping impurities:
the absorption edge location dependence on the sample
position along the ingot and the shift of this edge to the
longwave range comparing to pure CdTe; two additional
absorption bands with peaks at 1 1.9 μm and
2 7.0 μm which differ along the ingot.
a)
b)
Fig. 1. Transmission spectra of CdTe:Cr crystals in the ranges
of intrinsic absorption (a) and transparence (b). The dopant
concentration is C0 = 1019 cm-3. Samples 1 to 3 are taken from
the initial, middle, and end parts of the ingot, respectively.
The confirmation of these anomalies relationship
with Cr impurities is their correlation with the Cr dopant
concentration, so far as the latter depends on the samples
position along the ingot.
Taking into account that the segregation coefficient
of Cr in CdTe is less than unity [3], the mentioned
peculiarities can be explained by inhomogeneous
distribution of the dopant in the grown crystal. The
higher Cr impurity concentration at the beginning of the
ingot can be caused by the concentrated overcooling at
the crystallization front. Thereby, the absorption edge
shift to the longwave region with the increasing dopant
concentration well correlates with the reported data
[4, 5].
The observed absorption band at 1 1.9 μm,
according to the literature data [6], is characteristic for
Cr2+ ions in the CdTe lattice and induced by the intra-
center transitions from the ground level 5T2 to the
excited level 5Е. Just by these terms the ground 5D level
of an isolated Cr2+ (3d4) ion becomes splitted in the
CdTe crystalline field with the Тd-symmetry [6]. The
confirmation of such explanation is the dependence of
absorption band intensity on the impurity concentration.
As the intensity of the absorption band at
2 7.0 μm is also determined by the Cr concentration,
one can suppose that it is induced by the intra-center
transitions in the Cr ion that is in another charge state.
The possibility of impurities with unoccupied 3d-shells
to be in different charge states in II-VI compounds was
ascertained in the works [7, 8]. There is the highest
probability to suggest that the absorption band at
2 7.0 μm corresponds to the intra-center transitions
4T1(F)4T2(F) in Cr3+ ion.
Fig. 2. The photoluminescence spectra (T = 4.2 K) of CdTe
samples: 1 – undoped and Cr-doped with various
concentrations C0 (cm-3): 2 – 21017, 3 – 1018, 4 – 41019.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2010. V. 13, N 1. P. 91-94.
© 2010, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
93
Photoluminescence spectra. To fuller investigate the Cr
impurity influence on the CdTe optical properties, we
studied also CdTe:Cr crystal photoluminescence spectra
along with those for pure CdTe material obtained under
the same technological conditions.
It is possible to separate some groups of lines
inherent to the pure CdTe crystal photoluminescence
spectrum (Fig. 2, curve 1). In accord with the literature
data [9], the shortest wavelength band with its peak at
1.59 eV is related with annihilation of the exciton
bounded to the shallow acceptor (EA1 = Ev+0.05 eV). The
intensive band with the energy 1.547 eV that
corresponds to the phononless transition of edge
luminescence is formed due to electron transition from
the conduction band to the shallow acceptor [9]. The
energy location of noticed acceptor level, taking into
account the value Eg = 1.606 еV at 4.2 K, is determined
as EA1 = Ev+0.059 еV. The determined value EA1 is very
close to the acceptor location Ev+0.05 eV, which is
created in the CdTe material that was grown at a low Cd
vapour pressure and is related to the isolated singly
ionized Cd vacancy or to the complex with its
participation [9]. The closest two longwave bands are
the LO-phonon recurrence of the noticed band (for the
CdTe hLO = 0.021 eV). The wide photoluminescence
region at 1.42 eV is typical for CdTe [9]. Beside the
electron transition, it is characterized by a number of
emission peaks related to the various quantity of optic
LO phonons. This band can be explained by the
transition to the acceptor centers with the energy
location EA2 = Ev+(0.12-0.18) еV. These defects are
considered to have a complex nature, and they consist of
shallow acceptors and doubly ionized Cd vacancies (A-
centers) [10]. It is the most probable to suggest that the
A-centers in the investigated crystals are created by the
influence of background p-type impurities.
Significant changes in the CdTe luminescent
spectrum are observed at a relatively low concentration
of impurities (C0 = 317 cm102 ). Injection of Cr atoms
into CdTe lattice causes entire disappearance of exciton
luminescence, strong quenching the edge luminescence
at 1.42 eV as well as the appearance of additional
luminescence in the region close to 1.22 eV. At the
highest Cr concentration (C0 = 319 cm104 ) the
luminescence spectrum practically consists of one
emission band with the peak close to 1.22 eV. As far as
the acceptors А1(Ev+0.05 еV) and А2(Ev+(0.12-0.18) eV)
can be interpreted as CdV and DVCd [9, 10], the
observed quenching of the appropriate luminescence
bands at Cr concentration increase is due to the decrease
of VCd vacancies density because of dilution of Cr atoms
in the cadmium sublattice. It is necessary to underline
that the donor-acceptor couples radiation quenching
takes place because of injection of the Fe impurity [11]
as well as the elements of the IV group Ge, Sn, Pb
[12, 13] into the CdTe lattice.
A feature of the additional emission band in
photoluminescence spectra of CdTe:Cr crystals is the
dependence of the peak position on the dopant
concentration. Its shift to short wavelengths with
increasing the Cr impurity concentration from 1.225 eV
for С0 = 317 cm102 to 1.247 еV for С0 = 319 cm104
is observed. It indicates a complex nature of Cr-induced
defects, the transitions to which is the reason of origin of
the mentioned PL. The obtained results are well
correlated with the reported results [5]. The authors of
this work had determined the existence of deep level for
the CdTe:Cr crystals with different impurity
concentration, responsible for the equilibrium
conductivity within the energy range Ev+(0.19-0.32) еV.
These centers are related to the Cr impurities in Cr+1
charge state, which act as the deep donors in the case of
impurity clusterization. Taking into account the energy
gap Eg value, the described photoluminescence band
registered by us in CdTe:Cr crystals within the energy
range (1.225-1.247) еV can be explained by electron
transitions from the conduction band to the energy levels
Ev+(0.36-0.38) eV, which is in good agreement with the
ionization energy value Ev+0.32 еV reported in that
work.
The absence of exciton luminescence and
absorption edge shift to the longwave region after
injection of Cr atoms into CdTe lattice observed in this
work can be related to the specific impurity properties. It
is necessary to underline that the questions concerning
the reasons of the absorption edge shift in the CdTe:Cr
crystals and dependence of its value on the impurities
concentration have been discussed for a long time. It is
usually considered that the reason is strong lattice
deformation characteristic for the Cr2+ ions in CdTe near
the impurity location because of the static Jahn-Teller
effect [6]. In addition, the Cd2+ ion substitution by Cr2+
one can cause lattice deformation due to the difference
in ion radii (0.96 and 0.83 Å, respectively). This local
lattice deformation, at a definite dopant concentration,
can cause destruction of the exciton states and also
induce an additional absorption near the absorption
edge [4].
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