Optical properties and structure of As-Ge-Se thin films
Thin chalcogenide films with compositions As₁₀Ge₂₂.₅Se₆₇.₅ and As₁₂Ge₃₃Se₅₅ have been investigated. Optical constants and thicknesses of these films were obtained from transmission spectra. Structure of initial bulk glasses and films were investigated by Raman spectroscopy. Both films are estimat...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2010
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| Цитувати: | Optical properties and structure of As-Ge-Se thin films / I.D. Tolmachov, A.V. Stronski, M. Vlcek // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2010. — Т. 13, № 3. — С.276-279. — Бібліогр.: 14 назв. — англ. |
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irk-123456789-1184042017-05-31T03:06:16Z Optical properties and structure of As-Ge-Se thin films Tolmachov, I.D. Stronski, A.V. Vlcek, M. Thin chalcogenide films with compositions As₁₀Ge₂₂.₅Se₆₇.₅ and As₁₂Ge₃₃Se₅₅ have been investigated. Optical constants and thicknesses of these films were obtained from transmission spectra. Structure of initial bulk glasses and films were investigated by Raman spectroscopy. Both films are estimated to have high values of the nonlinear refractive index. 2010 Article Optical properties and structure of As-Ge-Se thin films / I.D. Tolmachov, A.V. Stronski, M. Vlcek // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2010. — Т. 13, № 3. — С.276-279. — Бібліогр.: 14 назв. — англ. 1560-8034 PACS 42.70.Mp, 64.75.St, 78.66.-w http://dspace.nbuv.gov.ua/handle/123456789/118404 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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Thin chalcogenide films with compositions As₁₀Ge₂₂.₅Se₆₇.₅ and As₁₂Ge₃₃Se₅₅
have been investigated. Optical constants and thicknesses of these films were obtained
from transmission spectra. Structure of initial bulk glasses and films were investigated by
Raman spectroscopy. Both films are estimated to have high values of the nonlinear
refractive index. |
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Article |
| author |
Tolmachov, I.D. Stronski, A.V. Vlcek, M. |
| spellingShingle |
Tolmachov, I.D. Stronski, A.V. Vlcek, M. Optical properties and structure of As-Ge-Se thin films Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Tolmachov, I.D. Stronski, A.V. Vlcek, M. |
| author_sort |
Tolmachov, I.D. |
| title |
Optical properties and structure of As-Ge-Se thin films |
| title_short |
Optical properties and structure of As-Ge-Se thin films |
| title_full |
Optical properties and structure of As-Ge-Se thin films |
| title_fullStr |
Optical properties and structure of As-Ge-Se thin films |
| title_full_unstemmed |
Optical properties and structure of As-Ge-Se thin films |
| title_sort |
optical properties and structure of as-ge-se thin films |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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2010 |
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http://dspace.nbuv.gov.ua/handle/123456789/118404 |
| citation_txt |
Optical properties and structure of As-Ge-Se thin films / I.D. Tolmachov, A.V. Stronski, M. Vlcek // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2010. — Т. 13, № 3. — С.276-279. — Бібліогр.: 14 назв. — англ. |
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Semiconductor Physics Quantum Electronics & Optoelectronics |
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AT tolmachovid opticalpropertiesandstructureofasgesethinfilms AT stronskiav opticalpropertiesandstructureofasgesethinfilms AT vlcekm opticalpropertiesandstructureofasgesethinfilms |
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2025-07-08T13:54:50Z |
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2025-07-08T13:54:50Z |
| _version_ |
1837087212158582784 |
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Semiconductor Physics, Quantum Electronics & Optoelectronics, 2010. V. 13, N 3. P. 276-279.
PACS 42.70.Mp, 64.75.St, 78.66.-w
Optical properties and structure of As-Ge-Se thin films
I.D. Tolmachov1, A.V. Stronski1, M. Vlcek2
1V. Lashkaryov Institute of Semiconductor Physics, NAS Ukraine,
41, prospect Nauky, 03028 Kyiv, Ukraine
2University of Pardubice, Faculty of Chemical Technology,
Studentská 573, 532 10 Pardubice, Czech Republic
E-mail: tolmach_igor@mail.ru
Abstract. Thin chalcogenide films with compositions As10Ge22.5Se67.5 and As12Ge33Se55
have been investigated. Optical constants and thicknesses of these films were obtained
from transmission spectra. Structure of initial bulk glasses and films were investigated by
Raman spectroscopy. Both films are estimated to have high values of the nonlinear
refractive index.
Keywords: chalcogenide films, optical properties, nonlinearity, Raman spectra.
Manuscript received 12.02.10; accepted for publication 08.07.10; published online 30.09.10.
1. Introduction
© 2010, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
( )
Chalcogenide glassy semiconductors (ChGS) are
attracting attention of many researches since the
discovery of their semiconductor properties in the 1950s.
This is due to their unique properties such as
transparency in infrared region of spectrum, high
stability and a number of photoinduced phenomena
(photodarkening, photobleaching, photocrystallization,
etc.). Recently, high attention has been paid to the
nonlinear optical properties of ChGS. Measurements of
nonlinear refractive index have shown that its value can
range from 100 to 1000 times of that in silica glass. High
nonlinear refractive index combined with moderate to
low nonlinear absorption can be exploited in all optical
signal processing devices to enhance performances of
telecommunication systems. ChGS are very suitable for
these kinds of applications, because they are compatible
with well established silica-on-silicon and fiber drawing
technologies. The nature of glassy state provides an
opportunity to adjust the composition and therefore, to
tune smoothly the properties of material. Photoinduced
phenomena allow the local modification of the material
properties by the exposure to suitable radiation which
can be utilized in writing waveguide channels,
diffraction gratings and so forth.
Quite complicated experimental techniques are
exploited for determination of nonlinear refractive index.
To avoid these difficulties several semiempirical
relations have been proposed in literature to estimate the
nonlinear refractive index or third order nonlinear
susceptibility from other known parameters such as the
linear refractive index, first order susceptibility, bandgap
energy, etc.
The most simple of these relations is based on using
the generalized Miller’s rule [1]. According to this rule,
third order nonlinear susceptibility can be estimated as
( )41)3( χ≅χ A
4
2 / gEBn ≈
, (1)
where A stands for a constant, the value of which for
chalcogenides appears to be A = 1.7·10–10 when χ(3) value
are obtained in esu units.
Authors of [1] also derived another formula that
relates nonlinear refractive index to the bandgap of
material:
, (2)
where B = 1.26·10-9 esu·eV4.
Boling et al. [2] have derived several relations, the
simplest of which is:
n2 (10–13esu) ≈ 391(nd – 1)/νd
5/4 , (3)
where nd stands for the refractive index at the d-line (λ =
588 nm) and νd stands for the Abbe number. This
relation contains only these two linear macroscopic
parameters, which can be easily evaluated. Accordingly,
this formula has been frequently utilized for estimations
276
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2010. V. 13, N 3. P. 276-279.
of n2. It provides a good approximation for small nd
glasses with nd ≤ 1.7 [3]. For high nd glasses, Lines [4]
has proposed a relation that takes the atomic distance
into consideration, too.
Since all the above mentioned formulas do not
contain the wavelength, they cannot predict the
dispersion dependence of nonlinear refraction, and all
the obtained nonlinear parameters may be regarded as
long-wavelength limit values.
Recently, Sanghera et al. [5] proposed to relate
nonlinearity to the normalized bandgap that is a measure
of how far the pump is from the band edge via the
classical anharmonic oscillator model:
42
632
4
)3( 11
3
−
⎥
⎥
⎥
⎦
⎤
⎢
⎢
⎢
⎣
⎡
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛ ν
−≈χ
gg E
h
Emd
Ne , (4)
where hν is the incident photon energy, N, d and m are
constants (material properties), Eg is the bandgap. Values
of n2 were measured independently for silica glasses,
some oxides and chalcogenides and plotted in the form
of function
⎟
⎟
⎟
⎠
⎞
⎜
⎜
⎜
⎝
⎛
⎥
⎥
⎦
⎤
⎢
⎢
⎣
⎡
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛ ν
−=
−4
62 11
gg E
h
E
fn (5)
representing the results obtained by authors of the work
as well as literature data at two wavelengths: 1250 and
1550 nm. All these values were fitted well by a straight
line indicating the usability of Sanghera´s method.
Measurements of nonlinear refraction of different
ChGS have shown that selenide glasses poses one of the
highest values of n2 among other chalcogenides. This is
usually attributed to the high polarizability of Se atoms.
Therefore, in this paper we studied Se-based
chalcogenide glasses in the ternary As-Ge-Se system.
2. Experimental
In this work, we have examined thin chalcogenide films
of two compositions: As10Ge22.5Se67.5 and As12Ge33Se55.
Initial bulk glasses of the mentioned compositions
were prepared by direct synthesis in evacuated silica
ampoules. After the synthesis, ampoules were water-
quenched. Thin films were obtained by thermal vacuum
evaporation onto the glass substrate at room temperature.
Optical transmission spectra of these films were
measured in the 0.4–2.5 μm range. Optical constants,
optical bandgap, Eg, refractive index in the longwave
limit, n0, and thicknesses of these films were
determinated from transmission spectra using the
method proposed by Swanepoel [6].
Raman spectra of initial bulk glasses and thin films
were investigated using IR Fourier spectrophotometer
Bruker IFS55 Equinox with FRA-106 attachment. Nd-
YAG laser operating at the wavelength 1.064 μm was
used as a pumping source.
3. Results and discussion
Fig. 1 shows the spectral dependence of refractive index
of As12Ge33Se55 thin film obtained by Swanepoel’s
method [6] from transmission spectrum. Solid line
shows fitting of the dependence by the function:
( ) can +
λ
=λ
2
. (6)
In Fig. 2, the energy dependence of (αE)½
parameter is plotted. Linear range in the region of high
photon energies corresponds to the Tauc law that was
used to determine optical bandgap, Eg. Its value is given
by the point where this line intersects with abscissa (see
Fig. 2).
Optical properties and thicknesses of the films
obtained from transmission spectra are listed in Table,
where Eg is the optical bandgap and n0 is refractive index
in the longwave limit.
Raman spectra of initial bulk glasses As10Ge22.5Se67.5
and As12Ge33Se55 are shown in Figs 3a and 3b,
respectively. The main band in spectra of both glasses
located near 200 cm-1 is a characteristic band of As-Ge-Se
glasses. In the case of As12Ge33Se55 glass it is centered at
192 cm-1 and contains two shoulders at 178 and 215 cm-1.
The mode at 216 cm-1 is also present in the
As10Ge22.5Se67.5 as a distinguished peak. In both glasses,
there is a broad band near 250 cm-1 that has two maxima
located at 241 and 254 cm-1 in the case of As10Ge22.5Se67.5
glass and at 240 and 253 cm-1 in the case of As12Ge33Se55
glass. In the low frequency region of both spectra, there
are maxima near 80, 105, and 140 cm-1 that are more
pronounced in the case of As12Ge33Se55 glass.
In Fig. 4, Raman spectrum of As10Ge22.5Se67.5 thin
film is presented. As can be seen, it is very similar to the
spectrum of corresponding bulk glass (Fig. 3a). The
main difference between them lies in comparable
intensities of the Raman modes. The modes near 145,
215, 240 and 250 cm-1 have larger intensity (in relation
to the main band) in the spectrum of the film.
Fig. 1. Spectral dependence of the refractive index of
As12Ge33Se55 thin film.
© 2010, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
277
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2010. V. 13, N 3. P. 276-279.
Table. Films’ parameters obtained from transmission spectra.
Composition Film thickness, nm Eg, eV n0
As12Ge33Se55 788 1.67 2.34
As10Ge22.5Se67.5 1070 1.93 2.28
© 2010, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
1,0 1,5 2,0 2,5
0
100
200
300
400
500
600
Eg = 1.93 eV
(α
hν
)1/
2 , c
m
-1
/2
eV
-1
/2
E, eV
Fig. 2. Tauc plot for As10Ge22.5Se67.5 film.
100 200 300 400
0
1
2
3
4
5
In
te
ns
ity
, (
a.
u.
)
Wavenumber, cm-1
144
200
216
241
254
105
84
a
100 200 300
0
1
2
3
4
5
In
te
ns
ity
, (
a.
u.
)
Wavenumber, cm-1
192
178
215
253
140
104
84
240
b
Fig. 3. Raman spectra of initial bulk glasses
As10Ge22.5Se67.5 (a) and As12Ge33Se55 (b).
200 300
0
1
2
3
4
5
145
In
te
ns
ity
, a
.u
.
Wavenumber, cm-1
215
197
239
259
Fig. 4. Raman spectrum of As10Ge22.5Se67.5 thin film.
The main band near 200 cm-1 and the mode at
215 cm-1 corresponds to the vibrations in corner-shared
and edge-shared Ge(Se1/2)4 tetrahedra [7], respectively, in
both glasses. However, in the case of As12Ge33Se55 glass,
this band obviously possesses more complicated shape.
The most distinguishable difference is the feature near
178 cm-1. The latter can be ascribed to the presence of Ge-
Ge bonds that are located in the Ge2(Se1/2)6 ethane-like
structural units [7]. These structural units appear to be
demixed from the network of the glass and form separate
nanophase inclusions in the overall glass backbone [8].
Since the ethane-like phase has two Raman active modes
located at 178 and 202 cm-1 [9], we can see that the main
band of the spectrum of As12Ge33Se55 glass is the
superposition of these bands of corner-shared and edge-
shared Ge(Se1/2)4 tetrahedra and two bands of Ge2(Se1/2)6
ethane-like nanophase. The mentioned nanophase
segregates from the backbone of the glass to
accommodate Se deficiency in the As12Ge33Se55 glass.
Three lower frequency bands near 80, 105, and
140 cm-1 along with the bands near 240 and 253 cm-1
represent vibration modes of amorphous selenium [10].
The bands at 80, 112 and 250 cm-1 are characteristic of
the Se8 rings and their fragments with 5 and 6 atoms.
The bands at 140 and 240 cm-1 are ascribed to the
vibrations in Sen polymeric chains. The broad band near
250 cm-1 also contains the overlapping contribution from
the vibrations in As(Se1/2)3 pyramidal units that are parts
of the glass network.
The increase of the relative intensities of bands
near 145, 240 and 250 cm-1 in the spectrum of
As10Ge22.5Se67.5 thin film can be attributed to the higher
concentration of Se molecular units and/or polymeric
chains. The mode at 215 cm-1 is increased due to
augmentation of the number of edge-shared Ge(Se1/2)4
tetrahedral units, which is necessary as the total amount
of Se in this material remains the same as in the
corresponding bulk glass.
278
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2010. V. 13, N 3. P. 276-279.
Fig. 5. Phase diagram of As-Ge-Se system [11]. The
intermediate phase is shown by the hashed region between the
floppy and stressed rigid phases. Nanoscale phase-separated
alloys are shown by grey shading. Compositions under
investigation are marked with the numbers: 1 for
As10Ge22.5Se67.5, and 2 for As12Ge33Se55.
The phase diagram of As-Ge-Se system is
presented in Fig. 5 [11]. According to the structure
classification proposed by Phillips et al. [11], there exist
three regions: (1) floppy phase, (2) intermediate phase
(hashed region in Fig. 5), and (3) stressed-rigid phase.
Compositions under investigation are shown in Fig. 5 as
spots marked by numbers: 1 for As10Ge22.5Se67.5, and
2 for As12Ge33Se55. In the binary As-Se and Ge-Se
systems, stressed rigid glasses are nanoscale phase-
separated. However, the investigations of the ternary
glasses AsxGexSe1-2x containing equal concentrations of
As and Ge have shown that these glasses appear to be
fully polymerized. Detection of the ethane-like
nanophase in As12Ge33Se55 proves that this glass falls
into the region of nanoscale phase-separated alloys.
To characterize the nonlinear optical properties of
the obtained films, we estimated nonlinear refractive
indexes of the films at the telecommunication
wavelength (λ = 1550 nm) using the formula (4).
Estimation gave n2 = 3.7·10-17 m2/W for As12Ge33Se55
film and n2 = 1.2·10-17 m2/W for As10Ge22.5Se67.5 film.
These results appeared to be in satisfactory agreement
with another results published on As-Ge-Se glasses [12-
14]. The obtained high values of third order nonlinearity
make these glasses suitable to be considered as
perspective materials for all-optical switching and other
optical signal processing applications.
4. Conclusions
Thin chalcogenide films with compositions
As10Ge22.5Se67.5 and As12Ge33Se55 have been investigated
in this paper. Transmission spectra measurements
allowed to determine optical constants of these films.
Both glasses possess high values of the third order
refractive index (n2 = 3.7·10-17 m2/W for As12Ge33Se55
film and n2 = 1.2·10-17 m2/W for As10Ge22.5Se67.5 film). It
makes them very promising materials for fabrication of
all-optical signal processing devices.
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© 2010, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
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