Optical absorption edge in (Ag₃AsS₃)x(As₂S₃)₁-x superionic glasses
The spectrometric studies of optical absorption edge in (Ag₃AsS₃)x(As₂S₃)₁-x superionic glasses were carried out within the temperature range 77 to 400 K. The influence of temperature and composition on the optical absorption edge, parameters of the Urbach absorption edge, parameters of electron...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2012
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nasplib_isofts_kiev_ua-123456789-1182852025-06-03T16:28:47Z Optical absorption edge in (Ag₃AsS₃)x(As₂S₃)₁-x superionic glasses Studenyak, I.P. Kranjcec, M. Neimet, Yu.Yu. Pop, M.M. The spectrometric studies of optical absorption edge in (Ag₃AsS₃)x(As₂S₃)₁-x superionic glasses were carried out within the temperature range 77 to 400 K. The influence of temperature and composition on the optical absorption edge, parameters of the Urbach absorption edge, parameters of electron-phonon interaction as well as ordering-disordering processes in (Ag₃AsS₃)x(As₂S₃)₁-x superionic glasses are studied. 2012 Article Optical absorption edge in (Ag₃AsS₃)x(As₂S₃)₁-x superionic glasses/ I.P. Studenyak, M. Kranjcec, Yu.Yu. Neimet, M.M. Pop // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2012. — Т. 15, № 2. — С. 147-151. — Бібліогр.: 13 назв. — англ. 1560-8034 PACS 78.20.Ci, 78.40.Ha https://nasplib.isofts.kiev.ua/handle/123456789/118285 en Semiconductor Physics Quantum Electronics & Optoelectronics application/pdf Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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The spectrometric studies of optical absorption edge in (Ag₃AsS₃)x(As₂S₃)₁-x
superionic glasses were carried out within the temperature range 77 to 400 K. The
influence of temperature and composition on the optical absorption edge, parameters of
the Urbach absorption edge, parameters of electron-phonon interaction as well as
ordering-disordering processes in (Ag₃AsS₃)x(As₂S₃)₁-x superionic glasses are studied. |
| format |
Article |
| author |
Studenyak, I.P. Kranjcec, M. Neimet, Yu.Yu. Pop, M.M. |
| spellingShingle |
Studenyak, I.P. Kranjcec, M. Neimet, Yu.Yu. Pop, M.M. Optical absorption edge in (Ag₃AsS₃)x(As₂S₃)₁-x superionic glasses Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Studenyak, I.P. Kranjcec, M. Neimet, Yu.Yu. Pop, M.M. |
| author_sort |
Studenyak, I.P. |
| title |
Optical absorption edge in (Ag₃AsS₃)x(As₂S₃)₁-x superionic glasses |
| title_short |
Optical absorption edge in (Ag₃AsS₃)x(As₂S₃)₁-x superionic glasses |
| title_full |
Optical absorption edge in (Ag₃AsS₃)x(As₂S₃)₁-x superionic glasses |
| title_fullStr |
Optical absorption edge in (Ag₃AsS₃)x(As₂S₃)₁-x superionic glasses |
| title_full_unstemmed |
Optical absorption edge in (Ag₃AsS₃)x(As₂S₃)₁-x superionic glasses |
| title_sort |
optical absorption edge in (ag₃ass₃)x(as₂s₃)₁-x superionic glasses |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| publishDate |
2012 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/118285 |
| citation_txt |
Optical absorption edge in (Ag₃AsS₃)x(As₂S₃)₁-x superionic glasses/ I.P. Studenyak, M. Kranjcec, Yu.Yu. Neimet, M.M. Pop // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2012. — Т. 15, № 2. — С. 147-151. — Бібліогр.: 13 назв. — англ. |
| series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
| work_keys_str_mv |
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| first_indexed |
2025-12-02T10:51:54Z |
| last_indexed |
2025-12-02T10:51:54Z |
| _version_ |
1850393456625582080 |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2012. V. 15, N 2. P. 147-151.
© 2012, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
147
PACS 78.20.Ci, 78.40.Ha
Optical absorption edge in (Ag3AsS3)x(As2S3)1-x superionic glasses
I.P. Studenyak1, M. Kranjcec2, Yu.Yu. Neimet1, M.M. Pop1
1Uzhhorod National University, Physics Faculty,
46, Pidhirna str., 88000 Uzhhorod, Ukraine
2University of Zagreb, Geotechnical Faculty,
Hallerova Aleja 7, 42000 Varaždin, Croatia
E-mail: studenyak@dr.com
Abstract. The spectrometric studies of optical absorption edge in x132x33 SAsAsSAg
superionic glasses were carried out within the temperature range 77 to 400 K. The
influence of temperature and composition on the optical absorption edge, parameters of
the Urbach absorption edge, parameters of electron-phonon interaction as well as
ordering-disordering processes in x132x33 SAsAsSAg superionic glasses are studied.
Keywords: superionic glass, absorption edge, Urbach rule, electron-phonon interaction.
Manuscript received 10.02.12; revised version received 14.03.12; accepted for
publication 27.03.12; published online 30.05.12.
1. Introduction
Chalcogenide glasses are of a great interest at a
development of new solid electrolytes because of the
high values of their electrical conductivity in comparison
with oxide glasses [1]. One has to note that these highly
conductive glasses are transparent in the IR region,
which is very useful for the creation of functional
elements for optical devices. The unique combination of
various properties in chalcogenide glasses and a
possibility to change functional parameters during
modifications, i.e. a change of chemical composition and
production technology, influence of external factors,
lead to a wide range of their applications in holography
and microlithography, systems of information writing
and reading, optoelectronics, infrared and nonlinear
optics, sensorics, electronic technology, etc. [ 5-2 ].
Therefore, ternary Ag-S-As glasses are of a
considerable interest. The Ag-S-As glasses were
extensively studied, first of all, due to the potential
possibility of their application as a solid electrolyte [6, 7].
The nature of electrical conductivity – ionic or electronic –
depends mainly on a silver content in the given ternary
glasses, which, in its turn, influences the other physical
properties. The 3332 AsSAgSAs glasses are practically
unstudied yet.
Hence, as alluded to above, the main goals of the
paper are as follows: (i) temperature investigation of the
optical absorption edge, (ii) studying the temperature
behavior peculiarities of optical parameters and
(iii) studying the temperature, structural, compositional
disordering processes in x132x33 SAsAsSAg
superionic glasses.
2. Experimental
The (Ag3AsS3)x(As2S3)1-x vitreous alloys were obtained
by a vacuum (0.01 Pa) melting of the corresponding
mixture of As2S3 and Ag3AsS3 components, which were
synthesized beforehand from highly pure elemental
substances. The melt homogenization temperature was
820-840 K with the homogenization time 24 hours. The
melt was mixed periodically and thereafter quenched in
the ice water (273 K).
Spectrometric studies of the optical absorption edge
were carried out within the temperature range 77 to
400 K using LOMO KSVU-23 grating monochromator
[8]. For low temperature studies, the cryostat of UTREX
type was used, stability and accuracy of temperature
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2012. V. 15, N 2. P. 147-151.
© 2012, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
148
measurements were maintained at 0.5 K. The relative
error in determination of the absorption coefficient /
did not exceed 10% at 0.3 d 3 [8].
3. Results and discussion
The optical absorption edge of x132x33 SAsAsSAg
superionic glasses with x = 0.3…0.6 was carried out
within the temperature range T = 77…400 K. It was
revealed that the absorption edge for
(Ag3AsS3)0.3(As2S3)0.7 glass was strongly smeared and
had an exponential shape. With temperature increase, it
shifts towards longer wavelengths without the change of
a slope of exponential parts of the absorption edge
(Fig. 1a). With Ag3AsS3 content increase, the absorption
edge gets the Urbach shape. The latter is well seen
within the temperature ranges T = 250…400 K for
(Ag3AsS3)0.4(As2S3)0.6 glass (Fig. 1b), T = 150…400 K
for (Ag3AsS3)0.5(As2S3)0.5 glass (Fig. 1c) and T =
77…400 K for (Ag3AsS3)0.6(As2S3)0.4 glass (Fig. 1d). In
the case of Urbach behavior of the absorption edge, its
spectral and temperature dependences are described by
the well known relation [9]:
kT
Eh
Th 0
0 exp),( , (1)
where UEkT / is the steepness parameter of the
absorption edge, UE is Urbach energy or the energy
width of the exponential absorption edge, 0 and 0E
are coordinates of the convergence point inherent to the
Urbach bundle. For comparison, values of parameters
0 and 0E for As2S3 and x132x33 SAsAsSAg
glasses with х = 0.4, 0.5, 0.6 were shown in Table.
Hence, with х increase the respective growth of both
convergence point coordinates E0 and 0 is found to be
present.
Parameters of the electron-phonon interaction (EPI)
0 and p were estimated from the temperature
dependences of the absorption edge slope parameter
(see insets in Fig. 1) by the Mahr equation [10]:
kT
th
kT
T p
p 2
2
0
, (2)
where p is the effective average phonon energy in a
a b
c d
Fig. 1. Spectral dependences of the Urbach absorption edge for (Ag3AsS3)0.3(As2S3)0.7 (a), (Ag3AsS3)0.4(As2S3)0.6 (b),
(Ag3AsS3)0.5(As2S3)0.5 (c), and (Ag3AsS3)0.6(As2S3)0.4 (d) glasses at different temperatures: (a) 77 K (1), 200 (2), 250 (3),
300 (4), 350 (5), 400 (6); (b)-(d) 77 K (1), 150 (2), 200 (3), 250 (4), 300 (5), 350 (6), 400 (7). Insets show temperature
dependences of the absorption edge slope parameter
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2012. V. 15, N 2. P. 147-151.
© 2012, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
149
single-oscillator model, which describes the EPI; 0 –
parameter, related to the EPI constant g by the relation
0 = 2/3g. The parameters p and 0 for As2S3 and
x132x33 SAsAsSAg glasses with х = 0.4, 0.5, 0.6 are
shown in Table.
Fig. 2 illustrates the temperature dependences of
the optical pseudogap *
gE and Urbach energy UE that
are well described for x132x33 SAsAsSAg glasses at
х = 0.4, 0.5, 0.6 within the framework of the Einstein
model by equations [11, 12]:
1exp
1
0
T
kSETE
E
Eggg , (3)
1exp
1
)()( 10 T
EEE
E
UUU , (4)
where )0(*
gE and *
gS are the optical pseudogap at
T = 0 K and a dimensionless constant, respectively;
0)( UE and 1)( UE are constants; E is the Einstein
temperature corresponding to the average frequency of
phonon excitations of a system of non-coupled
oscillators. Parameters )0(*
gE , *
gS , 0)( UE , 1)( UE and
E for x132x33 SAsAsSAg glasses with х =
0.4, 0.5, 0.6, obtained from dependences TEg
* and
TEU , are summarized in Table.
With addition of Ag3AsS3 to the glassy matrix
As2S3 the absorption edge shifts towards longer
wavelengths, moreover, the optical pseudogap *
gE of
(Ag3AsS3)0.3(As2S3)0.7 glass decreases by 12% in
comparison with As2S3 (Fig. 3). At the same time,
transition of х from 0.3 to 0.6 makes no change in the
*
gE value (within 1%). Hereby, the Urbach energy UE
increases almost by 3 times in the glass with х = 0.3 in
contrast to the As2S3, and drops down afterwards almost
by 2 times and then stays almost unchanged (within 2%)
in the range х = 0.4…0.6.
a b
c d
Fig. 2. Temperature dependences of the optical pseudogap *
gE (1) and Urbach energy UE (2) for (Ag3AsS3)0.3(As2S3)0.7 (a),
(Ag3AsS3)0.4(As2S3)0.6 (b), (Ag3AsS3)0.5(As2S3)0.5 (c), and (Ag3AsS3)0.6(As2S3)0.4 (d) glasses.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2012. V. 15, N 2. P. 147-151.
© 2012, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
150
Table. Parameters of the Urbach absorption edge and EPI
for As2S3 (x = 0) and (Ag3AsS3)x(As2S3)1-x glasses (x =
0.3…0.6).
Glass As2S3 x = 0.3 x = 0.4 x = 0.5 x = 0.6
0 (cm-1) 2.97×105 – 2.61×106 2.78×107 4.86×107
E0 (eV) 2.605 – 2.644 2.790 2.853
*
gE (eV) 2.323 2.035 2.061 2.030 2.035
UE
(meV)
51.0 150.5 73.7 73.8 75.1
0 0.625 – 0.507 0.521 0.514
p
(meV)
43.9 – 62.6 65.6 66.3
E (K) 510 – 726 761 769
0)( UE
(meV)
35.1 – 61.7 62.9 64.5
1)( UE
(meV)
70.7 – 123.3 126.1 129.1
)0(*
gE
(eV)
2.395 – 2.163 2.142 2.158
*
gS 7.6 – 16.9 19.3 21.9
Compositional studies reveal the reduction of the
parameter 0 almost by 20% with x in
x132x33 SAsAsSAg glasses. Furthermore, as х
increases from 0.4 to 0.6, the value 0 slightly changes
(within 1%) (Fig. 4). Like to As2S3 glass,
x132x33 SAsAsSAg glasses of the given ternary
system have the parameter 10 , which is an evidence
of a strong EPI. Thus, with addition of Ag3AsS3 to
As2S3, strengthening the EPI (i.e. decrease of the 0
value) is apparent, whereas the effective phonon energy
substantially expands by 43% as compared with As2S3
and also increases with x (Fig. 4).
Fig. 3. Compositional dependences of the optical pseudogap
*
gE (1) and Urbach energy UE (2) for (Ag3AsS3)x(As2S3)1-x
glasses.
Fig. 4. Compositional dependences of the parameter 0 (1) and
effective phonon energy p (2) for x132x33 SAsAsSAg
glasses.
We note that besides the temperature and structural
types of disordering (caused by thermal vibrations of
atoms and structural elements on the one hand, and by
defects and impurities of a structure and absence of a
long-range order in atomic arrangement on the other
hand), x132x33 SAsAsSAg glasses have additionally
manifested compositional one caused by addition of
Ag3AsS3 into As2S3. According to [13], the effects of an
influence of different types of disordering on the Urbach
energy in solid solution are described by the relation
TUCXUCUTUXUU EEEEEE )()()()()( , , (5)
where XUE )( and CUE )( are contributions of structural
and compositional disordering to the Urbach energy UE ,
respectively; TUE )( is a contribution of temperature
disordering to UE . Comparison of two equations (4) and
(5) evidences that 0, )()( UCXU EE and
1)/(exp)()( 1 TEE EUTU . Thus, the
contributions of temperature independent CXUE ,)(
(structural and compositional) and temperature
dependent TUE )( disordering were differentiated. Their
compositional dependences are shown in Fig. 5. It is
seen that CXUE ,)( contribution is prevailing and for
As2S3 turns out to be 69% of the UE value. With
addition of Ag3AsS3 the CXUE ,)( contribution grows up
to 84% for х = 0.3, and then increases for a bit with х
growth (the contribution CXUE ,)( to UE for х = 0.6 is
equal to 86%).
Consequently, smearing the absorption edge at Т =
300 K with an Ag3AsS3 content increase in
x132x33 SAsAsSAg glasses occurs mostly due to
temperature independent types of disordering, or, in
other words, is determined by contributions of structural
and compositional disordering (Fig. 5).
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2012. V. 15, N 2. P. 147-151.
© 2012, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
151
Fig. 5. Compositional dependences of contributions of
temperature independent CXUE ,)( (1) and temperature
dependent TUE )( (2) types of disordering for
x132x33 SAsAsSAg glasses.
4. Conclusions
It has been shown in this paper that the absorption edge
for (Ag3AsS3)0.3(As2S3)0.7 glass is strongly smeared and
has an exponential shape. With temperature increase the
exponential part of the absorption edge shifts towards
longer wavelengths, while their slope remains
unchanged. With x increasing the absorption edge
becomes of the Urbach shape and keeps it in the
following temperature ranges: T = 250…400 K for
(Ag3AsS3)0.4(As2S3)0.6 glass, at T = 150…400 K for
(Ag3AsS3)0.5(As2S3)0.5 glass, and at T = 77…400 K for
(Ag3AsS3)0.6(As2S3)0.4 glass.
Parameters of electron-phonon interaction are
obtained from temperature dependences of the absorption
edge slope parameter . It was found that with addition of
Ag3AsS3 to As2S3 EPI becomes stronger, i.e. the value
decreases, whereas the effective phonon energy increases
by 43% as compared with pure As2S3.
Temperature dependences of such parameters
inherent to the Urbach absorption edge as the optical
pseudogap *
gE and Urbach energy UE are well
described within the framework of the Einstein model.
With Ag3AsS3 content increase, one can observe a
nonlinear decrease of *
gE . Moreover, the Urbach energy
UE grows by almost three times in the glass with х = 0.3
in comparison with As2S3, and then decreases by almost
two times and subsequently remains almost unchanged
(within 2%) in the compositional range х = 0.4…0.6.
The contributions of the temperature independent
(i.e. structural and compositional) and temperature
dependent disordering to the Urbach energy were
estimated. It turns out that, with Ag3AsS3 content
increase in x132x33 SAsAsSAg glasses, smearing the
absorption edge takes place mostly due to the
temperature independent types of disordering.
References
1. E. Bychkov, A. Bychkov, A. Pradel, M. Ribes,
Percolation transition in Ag-doped chalcogenide
glasses: comparison of classical percolation and
dynamic structure models // Solid State Ionics, 691,
p. 113-115 (1998).
2. M. Frumar, T. Wagner, Ag doped chalcogenide
glasses and their applications // Current Opinions
in Solid State and Math. Sci. 7, p. 117-126 (2003).
3. J. Dikova, P. Sharlandjiev, P. Gushterova,
Tz. Babeva, Photoinduced changes in the optical
properties of obliquely deposited a-As2S3 thin films
// Vacuum, 69, p. 395-398 (2003).
4. H. Jeong, S.-T. Hwang, K. Cho, Quantitative
analysis of photoinduced phenomena in amorphous
As2S3 thin films using the scanning homodyne
multiport interferometer // Opt. Communs. 249,
p. 225-230 (2005).
5. S. Stehlik, J. Kolar, M. Frumar, and T. Wagner,
Phase separation in chalcogenide glasses: The
system AgAsSSe // Intern. J. Appl. Glass Sci. 2,
p. 301-307 (2011).
6. E. Bychkov, Superionic and ion-conducting
chalcogenide glasses: Transport regimes and
structural features // Solid State Ionics, 180, p. 510-
516 (2009).
7. E. Bychkov, D.L. Price, C.J. Benmore,
A.C. Hannon, Ion transport regimes in
chalcogenide and chalcohalide glasses: from the
host to the cation-related network connectivity //
Solid State Ionics, 154–155, p. 349-359 (2002).
8. I.P. Studenyak, M. Kranjčec, and M.V. Kurik,
Urbach rule and disordering processes in
yy15xx16 IBr)SeP(SCu superionic conductors // J.
Phys. Chem. Solids, 67, p. 807-817 (2006).
9. F. Urbach, The long-wavelength edge of
photographic sensitivity and of the electronic
absorption of solids // Phys. Rev. 92, p. 1324
(1953).
10. M.V. Kurik, Urbach rule // Phys. Stat. Sol. (a) 8,
p. 9 (1971).
11. M. Beaudoin, A.J.G. DeVries, S.R. Johnson,
H. Laman, T. Tiedje, Optical absorption edge of
semi-insulating GaAs and InP at high temperatures
// Appl. Phys. Lett. 70, p. 3540 (1997).
12. Z. Yang, K.P. Homewood, M.S. Finney,
M.A. Harry, K.J. Reeson, Optical absorption study
of ion beam synthesised polycrystalline
semiconducting FeSi2 // J. Appl. Phys. 78, p. 1958
(1995).
13. G.D. Cody, T. Tiedje, B. Abeles, B. Brooks, and
Y. Goldstein, Disorder and the optical-absorption
edge of hydrogenated amorphous silicon // Phys.
Rev. Lett. 47, p. 1480-1483 (1981).
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2012. V. 15, N 2. P. 147-151.
PACS 78.20.Ci, 78.40.Ha
Optical absorption edge in (Ag3AsS3)x(As2S3)1-x superionic glasses
I.P. Studenyak1, M. Kranjcec2, Yu.Yu. Neimet1, M.M. Pop1
1Uzhhorod National University, Physics Faculty,
46, Pidhirna str., 88000 Uzhhorod, Ukraine
2University of Zagreb, Geotechnical Faculty,
Hallerova Aleja 7, 42000 Varaždin, Croatia
E-mail: studenyak@dr.com
Abstract. The spectrometric studies of optical absorption edge in
(
)
(
)
x
1
3
2
x
3
3
S
As
AsS
Ag
-
superionic glasses were carried out within the temperature range 77 to 400 K. The influence of temperature and composition on the optical absorption edge, parameters of the Urbach absorption edge, parameters of electron-phonon interaction as well as ordering-disordering processes in
(
)
(
)
x
1
3
2
x
3
3
S
As
AsS
Ag
-
superionic glasses are studied.
Keywords: superionic glass, absorption edge, Urbach rule, electron-phonon interaction.
Manuscript received 10.02.12; revised version received 14.03.12; accepted for publication 27.03.12; published online 30.05.12.
1. Introduction
Chalcogenide glasses are of a great interest at a development of new solid electrolytes because of the high values of their electrical conductivity in comparison with oxide glasses [1]. One has to note that these highly conductive glasses are transparent in the IR region, which is very useful for the creation of functional elements for optical devices. The unique combination of various properties in chalcogenide glasses and a possibility to change functional parameters during modifications, i.e. a change of chemical composition and production technology, influence of external factors, lead to a wide range of their applications in holography and microlithography, systems of information writing and reading, optoelectronics, infrared and nonlinear optics, sensorics, electronic technology, etc. [
5
-
2
].
Therefore, ternary
Ag
-
S
-
As
glasses are of a considerable interest. The
Ag
-
S
-
As
glasses were extensively studied, first of all, due to the potential possibility of their application as a solid electrolyte [6, 7]. The nature of electrical conductivity – ionic or electronic – depends mainly on a silver content in the given ternary glasses, which, in its turn, influences the other physical properties. The
3
3
3
2
AsS
Ag
S
As
-
glasses are practically unstudied yet.
Hence, as alluded to above, the main goals of the paper are as follows: (i) temperature investigation of the optical absorption edge, (ii) studying the temperature behavior peculiarities of optical parameters and (iii) studying the temperature, structural, compositional disordering processes in
(
)
(
)
x
1
3
2
x
3
3
S
As
AsS
Ag
-
superionic glasses.
2. Experimental
The (Ag3AsS3)x(As2S3)1-x vitreous alloys were obtained by a vacuum (0.01 Pa) melting of the corresponding mixture of As2S3 and Ag3AsS3 components, which were synthesized beforehand from highly pure elemental substances. The melt homogenization temperature was 820-840 K with the homogenization time 24 hours. The melt was mixed periodically and thereafter quenched in the ice water (273 K).
Spectrometric studies of the optical absorption edge were carried out within the temperature range 77 to 400 K using LOMO KSVU-23 grating monochromator [8]. For low temperature studies, the cryostat of UTREX type was used, stability and accuracy of temperature measurements were maintained at (0.5 K. The relative error in determination of the absorption coefficient ((/( did not exceed 10% at 0.3 ( (d ( 3 [8].
3. Results and discussion
The optical absorption edge of
(
)
(
)
x
1
3
2
x
3
3
S
As
AsS
Ag
-
superionic glasses with x = 0.3…0.6 was carried out within the temperature range T = 77…400 K. It was revealed that the absorption edge for (Ag3AsS3)0.3(As2S3)0.7 glass was strongly smeared and had an exponential shape. With temperature increase, it shifts towards longer wavelengths without the change of a slope of exponential parts of the absorption edge (Fig. 1a). With Ag3AsS3 content increase, the absorption edge gets the Urbach shape. The latter is well seen within the temperature ranges T = 250…400 K for (Ag3AsS3)0.4(As2S3)0.6 glass (Fig. 1b), T = 150…400 K for (Ag3AsS3)0.5(As2S3)0.5 glass (Fig. 1c) and T = 77…400 K for (Ag3AsS3)0.6(As2S3)0.4 glass (Fig. 1d). In the case of Urbach behavior of the absorption edge, its spectral and temperature dependences are described by the well known relation [9]:
(
)
ú
û
ù
ê
ë
é
-
n
s
×
a
=
n
a
kT
E
h
T
h
0
0
exp
)
,
(
,
(1)
where
U
E
kT
/
=
s
is the steepness parameter of the absorption edge,
U
E
is Urbach energy or the energy width of the exponential absorption edge,
0
a
and
0
E
are coordinates of the convergence point inherent to the Urbach bundle. For comparison, values of parameters
0
a
and
0
E
for As2S3 and
(
)
(
)
x
1
3
2
x
3
3
S
As
AsS
Ag
-
glasses with х = 0.4, 0.5, 0.6 were shown in Table. Hence, with х increase the respective growth of both convergence point coordinates E0 and (0 is found to be present.
Parameters of the electron-phonon interaction (EPI)
0
s
and
p
w
h
were estimated from the temperature dependences of the absorption edge slope parameter (see insets in Fig. 1) by the Mahr equation [10]:
(
)
÷
÷
ø
ö
ç
ç
è
æ
w
×
÷
÷
ø
ö
ç
ç
è
æ
w
s
=
s
kT
th
kT
T
p
p
2
2
0
h
h
,
(2)
where
p
w
h
is the effective average phonon energy in a single-oscillator model, which describes the EPI; (0 – parameter, related to the EPI constant g by the relation (0 = 2/3g. The parameters
p
w
h
and (0 for As2S3 and
(
)
(
)
x
1
3
2
x
3
3
S
As
AsS
Ag
-
glasses with х = 0.4, 0.5, 0.6 are shown in Table.
Fig. 2 illustrates the temperature dependences of the optical pseudogap
*
g
E
and Urbach energy
U
E
that are well described for
(
)
(
)
x
1
3
2
x
3
3
S
As
AsS
Ag
-
glasses at х = 0.4, 0.5, 0.6 within the framework of the Einstein model by equations [11, 12]:
(
)
(
)
(
)
ú
û
ù
ê
ë
é
-
q
q
-
=
*
*
*
1
exp
1
0
T
k
S
E
T
E
E
E
g
g
g
,
(3)
(
)
ú
û
ù
ê
ë
é
-
q
+
=
1
exp
1
)
(
)
(
1
0
T
E
E
E
E
U
U
U
,
(4)
where
)
0
(
*
g
E
and
*
g
S
are the optical pseudogap at T = 0 K and a dimensionless constant, respectively;
0
)
(
U
E
and
1
)
(
U
E
are constants;
E
q
is the Einstein temperature corresponding to the average frequency of phonon excitations of a system of non-coupled oscillators. Parameters
)
0
(
*
g
E
,
*
g
S
,
0
)
(
U
E
,
1
)
(
U
E
and
E
q
for
(
)
(
)
x
1
3
2
x
3
3
S
As
AsS
Ag
-
glasses with х = 0.4, 0.5, 0.6, obtained from dependences
(
)
T
E
g
*
and
(
)
T
E
U
, are summarized in Table.
With addition of Ag3AsS3 to the glassy matrix As2S3 the absorption edge shifts towards longer wavelengths, moreover, the optical pseudogap
*
g
E
of (Ag3AsS3)0.3(As2S3)0.7 glass decreases by 12% in comparison with As2S3 (Fig. 3). At the same time, transition of х from 0.3 to 0.6 makes no change in the
*
g
E
value (within 1%). Hereby, the Urbach energy
U
E
increases almost by 3 times in the glass with х = 0.3 in contrast to the As2S3, and drops down afterwards almost by 2 times and then stays almost unchanged (within 2%) in the range х = 0.4…0.6.
Table. Parameters of the Urbach absorption edge and EPI for As2S3 (x = 0) and (Ag3AsS3)x(As2S3)1-x glasses (x = 0.3…0.6).
Glass
As2S3
x = 0.3
x = 0.4
x = 0.5
x = 0.6
(0 (cm-1)
2.97×105
–
2.61×106
2.78×107
4.86×107
E0 (eV)
2.605
–
2.644
2.790
2.853
*
g
E
(eV)
2.323
2.035
2.061
2.030
2.035
U
E
(meV)
51.0
150.5
73.7
73.8
75.1
(0
0.625
–
0.507
0.521
0.514
p
w
h
(meV)
43.9
–
62.6
65.6
66.3
(E (K)
510
–
726
761
769
0
)
(
U
E
(meV)
35.1
–
61.7
62.9
64.5
1
)
(
U
E
(meV)
70.7
–
123.3
126.1
129.1
)
0
(
*
g
E
(eV)
2.395
–
2.163
2.142
2.158
*
g
S
7.6
–
16.9
19.3
21.9
Compositional studies reveal the reduction of the parameter
0
s
almost by 20% with x in
(
)
(
)
x
1
3
2
x
3
3
S
As
AsS
Ag
-
glasses. Furthermore, as х increases from 0.4 to 0.6, the value
0
s
slightly changes (within 1%) (Fig. 4). Like to As2S3 glass,
(
)
(
)
x
1
3
2
x
3
3
S
As
AsS
Ag
-
glasses of the given ternary system have the parameter
1
0
<
s
, which is an evidence of a strong EPI. Thus, with addition of Ag3AsS3 to As2S3, strengthening the EPI (i.e. decrease of the
0
s
value) is apparent, whereas the effective phonon energy substantially expands by 43% as compared with As2S3 and also increases with x (Fig. 4).
Fig. 3. Compositional dependences of the optical pseudogap
*
g
E
(1) and Urbach energy
U
E
(2) for (Ag3AsS3)x(As2S3)1-x glasses.
Fig. 4. Compositional dependences of the parameter (0 (1) and effective phonon energy
p
w
h
(2) for
(
)
(
)
x
1
3
2
x
3
3
S
As
AsS
Ag
-
glasses.
We note that besides the temperature and structural types of disordering (caused by thermal vibrations of atoms and structural elements on the one hand, and by defects and impurities of a structure and absence of a long-range order in atomic arrangement on the other hand),
(
)
(
)
x
1
3
2
x
3
3
S
As
AsS
Ag
-
glasses have additionally manifested compositional one caused by addition of Ag3AsS3 into As2S3. According to [13], the effects of an influence of different types of disordering on the Urbach energy in solid solution are described by the relation
T
U
C
X
U
C
U
T
U
X
U
U
E
E
E
E
E
E
)
(
)
(
)
(
)
(
)
(
,
+
=
+
+
=
,
(5)
where
X
U
E
)
(
and
C
U
E
)
(
are contributions of structural and compositional disordering to the Urbach energy
U
E
, respectively;
T
U
E
)
(
is a contribution of temperature disordering to
U
E
. Comparison of two equations (4) and (5) evidences that
0
,
)
(
)
(
U
C
X
U
E
E
º
and
(
)
1
)
/
(
exp
)
(
)
(
1
-
q
º
T
E
E
E
U
T
U
. Thus, the contributions of temperature independent
C
X
U
E
,
)
(
(structural and compositional) and temperature dependent
T
U
E
)
(
disordering were differentiated. Their compositional dependences are shown in Fig. 5. It is seen that
C
X
U
E
,
)
(
contribution is prevailing and for As2S3 turns out to be 69% of the
U
E
value. With addition of Ag3AsS3 the
C
X
U
E
,
)
(
contribution grows up to 84% for х = 0.3, and then increases for a bit with х growth (the contribution
C
X
U
E
,
)
(
to
U
E
for х = 0.6 is equal to 86%).
Consequently, smearing the absorption edge at Т = 300 K with an Ag3AsS3 content increase in
(
)
(
)
x
1
3
2
x
3
3
S
As
AsS
Ag
-
glasses occurs mostly due to temperature independent types of disordering, or, in other words, is determined by contributions of structural and compositional disordering (Fig. 5).
Fig. 5. Compositional dependences of contributions of temperature independent
C
X
U
E
,
)
(
(1) and temperature dependent
T
U
E
)
(
(2) types of disordering for
(
)
(
)
x
1
3
2
x
3
3
S
As
AsS
Ag
-
glasses.
4. Conclusions
It has been shown in this paper that the absorption edge for (Ag3AsS3)0.3(As2S3)0.7 glass is strongly smeared and has an exponential shape. With temperature increase the exponential part of the absorption edge shifts towards longer wavelengths, while their slope remains unchanged. With x increasing the absorption edge becomes of the Urbach shape and keeps it in the following temperature ranges: T = 250…400 K for (Ag3AsS3)0.4(As2S3)0.6 glass, at T = 150…400 K for (Ag3AsS3)0.5(As2S3)0.5 glass, and at T = 77…400 K for (Ag3AsS3)0.6(As2S3)0.4 glass.
Parameters of electron-phonon interaction are obtained from temperature dependences of the absorption edge slope parameter . It was found that with addition of Ag3AsS3 to As2S3 EPI becomes stronger, i.e. the value decreases, whereas the effective phonon energy increases by 43% as compared with pure As2S3.
Temperature dependences of such parameters inherent to the Urbach absorption edge as the optical pseudogap
*
g
E
and Urbach energy
U
E
are well described within the framework of the Einstein model. With Ag3AsS3 content increase, one can observe a nonlinear decrease of
*
g
E
. Moreover, the Urbach energy
U
E
grows by almost three times in the glass with х = 0.3 in comparison with As2S3, and then decreases by almost two times and subsequently remains almost unchanged (within 2%) in the compositional range х = 0.4…0.6.
The contributions of the temperature independent (i.e. structural and compositional) and temperature dependent disordering to the Urbach energy were estimated. It turns out that, with Ag3AsS3 content increase in
(
)
(
)
x
1
3
2
x
3
3
S
As
AsS
Ag
-
glasses, smearing the absorption edge takes place mostly due to the temperature independent types of disordering.
References
1.
E. Bychkov, A. Bychkov, A. Pradel, M. Ribes, Percolation transition in Ag-doped chalcogenide glasses: comparison of classical percolation and dynamic structure models // Solid State Ionics, 691, p. 113-115 (1998).
2.
M. Frumar, T. Wagner, Ag doped chalcogenide glasses and their applications // Current Opinions in Solid State and Math. Sci. 7, p. 117-126 (2003).
3.
J. Dikova, P. Sharlandjiev, P. Gushterova, Tz. Babeva, Photoinduced changes in the optical properties of obliquely deposited a-As2S3 thin films // Vacuum, 69, p. 395-398 (2003).
4.
H. Jeong, S.-T. Hwang, K. Cho, Quantitative analysis of photoinduced phenomena in amorphous As2S3 thin films using the scanning homodyne multiport interferometer // Opt. Communs. 249, p. 225-230 (2005).
5.
S. Stehlik, J. Kolar, M. Frumar, and T. Wagner, Phase separation in chalcogenide glasses: The system AgAsSSe // Intern. J. Appl. Glass Sci. 2, p. 301-307 (2011).
6.
E. Bychkov, Superionic and ion-conducting chalcogenide glasses: Transport regimes and structural features // Solid State Ionics, 180, p. 510-516 (2009).
7.
E. Bychkov, D.L. Price, C.J. Benmore, A.C. Hannon, Ion transport regimes in chalcogenide and chalcohalide glasses: from the host to the cation-related network connectivity // Solid State Ionics, 154–155, p. 349-359 (2002).
8.
I.P. Studenyak, M. Kranjčec, and M.V. Kurik, Urbach rule and disordering processes in
y
y
1
5
x
x
1
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I
Br
)
Se
P(S
Cu
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superionic conductors // J. Phys. Chem. Solids, 67, p. 807-817 (2006).
9.
F. Urbach, The long-wavelength edge of photographic sensitivity and of the electronic absorption of solids // Phys. Rev. 92, p. 1324 (1953).
10.
M.V. Kurik, Urbach rule // Phys. Stat. Sol. (a) 8, p. 9 (1971).
11.
M. Beaudoin, A.J.G. DeVries, S.R. Johnson, H. Laman, T. Tiedje, Optical absorption edge of semi-insulating GaAs and InP at high temperatures // Appl. Phys. Lett. 70, p. 3540 (1997).
12.
Z. Yang, K.P. Homewood, M.S. Finney, M.A. Harry, K.J. Reeson, Optical absorption study of ion beam synthesised polycrystalline semiconducting FeSi2 // J. Appl. Phys. 78, p. 1958 (1995).
13.
G.D. Cody, T. Tiedje, B. Abeles, B. Brooks, and Y. Goldstein, Disorder and the optical-absorption edge of hydrogenated amorphous silicon // Phys. Rev. Lett. 47, p. 1480-1483 (1981).
� a� b
�c�d
Fig. 2. Temperature dependences of the optical pseudogap � EMBED Microsoft Equation 3.0 ��� (1) and Urbach energy � EMBED Microsoft Equation 3.0 ��� (2) for (Ag3AsS3)0.3(As2S3)0.7 (a), (Ag3AsS3)0.4(As2S3)0.6 (b), (Ag3AsS3)0.5(As2S3)0.5 (c), and (Ag3AsS3)0.6(As2S3)0.4 (d) glasses.
� a� b
�c �d
Fig. 1. Spectral dependences of the Urbach absorption edge for (Ag3AsS3)0.3(As2S3)0.7 (a), (Ag3AsS3)0.4(As2S3)0.6 (b), (Ag3AsS3)0.5(As2S3)0.5 (c), and (Ag3AsS3)0.6(As2S3)0.4 (d) glasses at different temperatures: (a) 77 K (1), 200 (2), 250 (3), 300 (4), 350 (5), 400 (6); (b)-(d) 77 K (1), 150 (2), 200 (3), 250 (4), 300 (5), 350 (6), 400 (7). Insets show temperature dependences of the absorption edge slope parameter
© 2012, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
147
*
g
E
U
E
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