Raman spectra of Ag- and Cu- photodoped chalcogenide films
Raman spectra of the chalcogenide vitreous layers (As₄₀S₆₀, As₄₀S₄₀Se₂₀, As₄₀Se₆₀ ) non-doped and photodoped by Ag, Cu were measured. The spectra were analyzed in terms of a molecular model. It was ascertained, that for the spectra of photodoped As₄₀S₆₀, As₄₀S₄₀Se₂₀ layers, the shift of the main ban...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
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irk-123456789-1198622017-06-11T03:02:27Z Raman spectra of Ag- and Cu- photodoped chalcogenide films Stronski, A.V. Vlcek, M. Stetsun, A.I. Sklenar, A. Shepeliavyi, P.E. Raman spectra of the chalcogenide vitreous layers (As₄₀S₆₀, As₄₀S₄₀Se₂₀, As₄₀Se₆₀ ) non-doped and photodoped by Ag, Cu were measured. The spectra were analyzed in terms of a molecular model. It was ascertained, that for the spectra of photodoped As₄₀S₆₀, As₄₀S₄₀Se₂₀ layers, the shift of the main bands to the high frequency side and the appearance of the additional scattering bands in the low frequency spectral range are characteristic features. For the spectra of photodoped As₄₀S₆₀ layers, such shift and significant increase in scattering were not observed. Variations in the Raman spectra with photodoping by Ag or Cu are consistent with the supposition concerning normal covalent and coordinative bond formation between metal additives and chalcogen atoms. 1999 Article Raman spectra of Ag- and Cu- photodoped chalcogenide films / A.V. Stronski, M. Vlcek, A.I. Stetsun, A. Sklenar, P.E. Shepeliavyi // Semiconductor Physics Quantum Electronics & Optoelectronics. — 1999. — Т. 2, № 1. — С. 63-68. — Бібліогр.: 37 назв. — англ. 1560-8034 PACS 78.30, 78.66, 82.20C http://dspace.nbuv.gov.ua/handle/123456789/119862 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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Raman spectra of the chalcogenide vitreous layers (As₄₀S₆₀, As₄₀S₄₀Se₂₀, As₄₀Se₆₀ ) non-doped and photodoped by Ag, Cu were measured. The spectra were analyzed in terms of a molecular model. It was ascertained, that for the spectra of photodoped As₄₀S₆₀, As₄₀S₄₀Se₂₀ layers, the shift of the main bands to the high frequency side and the appearance of the additional scattering bands in the low frequency spectral range are characteristic features. For the spectra of photodoped As₄₀S₆₀ layers, such shift and significant increase in scattering were not observed. Variations in the Raman spectra with photodoping by Ag or Cu are consistent with the supposition concerning normal covalent and coordinative bond formation between metal additives and chalcogen atoms. |
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Stronski, A.V. Vlcek, M. Stetsun, A.I. Sklenar, A. Shepeliavyi, P.E. |
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Stronski, A.V. Vlcek, M. Stetsun, A.I. Sklenar, A. Shepeliavyi, P.E. Raman spectra of Ag- and Cu- photodoped chalcogenide films Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Stronski, A.V. Vlcek, M. Stetsun, A.I. Sklenar, A. Shepeliavyi, P.E. |
| author_sort |
Stronski, A.V. |
| title |
Raman spectra of Ag- and Cu- photodoped chalcogenide films |
| title_short |
Raman spectra of Ag- and Cu- photodoped chalcogenide films |
| title_full |
Raman spectra of Ag- and Cu- photodoped chalcogenide films |
| title_fullStr |
Raman spectra of Ag- and Cu- photodoped chalcogenide films |
| title_full_unstemmed |
Raman spectra of Ag- and Cu- photodoped chalcogenide films |
| title_sort |
raman spectra of ag- and cu- photodoped chalcogenide films |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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1999 |
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http://dspace.nbuv.gov.ua/handle/123456789/119862 |
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Raman spectra of Ag- and Cu- photodoped chalcogenide films / A.V. Stronski, M. Vlcek, A.I. Stetsun, A. Sklenar, P.E. Shepeliavyi // Semiconductor Physics Quantum Electronics & Optoelectronics. — 1999. — Т. 2, № 1. — С. 63-68. — Бібліогр.: 37 назв. — англ. |
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Semiconductor Physics Quantum Electronics & Optoelectronics |
| work_keys_str_mv |
AT stronskiav ramanspectraofagandcuphotodopedchalcogenidefilms AT vlcekm ramanspectraofagandcuphotodopedchalcogenidefilms AT stetsunai ramanspectraofagandcuphotodopedchalcogenidefilms AT sklenara ramanspectraofagandcuphotodopedchalcogenidefilms AT shepeliavyipe ramanspectraofagandcuphotodopedchalcogenidefilms |
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2025-07-08T16:47:33Z |
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| fulltext |
63© 1999, Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
Semiconductor Physics, Quantum Electronics & Optoelectronics. 1999. V. 2, N 2. P. 63-68.
PACS 78.30, 78.66, 82.20C
Raman spectra of Ag- and Cu- photodoped
chalcogenide films
A. V. Stronski a*, M. Vlcek b, A. I. Stetsun a, A. Sklenar b, P. E. Shepeliavyi a
a - Institute of Semiconductor Physics of NASU, 45, prospect Nauki , 252028 Kiev, Ukraine
b - Pardubice University, Pardubice, Czech Republic
Abstract. Raman spectra of the chalcogenide vitreous layers (As40S60, As40S40Se20, As40Se60 ) non-
doped and photodoped by Ag, Cu were measured. The spectra were analyzed in terms of a molecular
model. It was ascertained, that for the spectra of photodoped As40S60, As40S40Se20 layers, the shift of
the main bands to the high frequency side and the appearance of the additional scattering bands in the
low frequency spectral range are characteristic features. For the spectra of photodoped As40Se60 layers,
such shift and significant increase in scattering were not observed. Variations in the Raman spectra with
photodoping by Ag or Cu are consistent with the supposition concerning normal covalent and coordina-
tive bond formation between metal additives and chalcogen atoms.
Keywords: arsenic chacogenides, thin films, photodoping, Raman spectroscopy.
Paper received 26.04.99; revised manuscript received 28.04.99; accepted for publication 12.07.99.
1. Introduction
Chalcogenide vitreous semiconductors ( ChVS) have high
transparency in the IR spectral range. This and other of
their specific properties enable one to use them as a me-
dia for light waveguides in optoelectronics and also in
the IR technique. Among the numerous photo- and ra-
diation-stimulated phenomena exhibited by ChVS - the
phenomenon of the photostimulated diffusion of metal
[1] (mainly Ag or Cu) into ChVS is one of the most inter-
esting. Under the illumination of the ChVS layer that
was deposited on the metal layer (or metal- containing
layer, the order of the layers can be reversed ) the inter-
action between substances in the semiconductor and
metal layers occurs with the creation of an interaction
product layer (photodoped layer). The phenomenon has
attracted the attention of numerous investigators, vari-
ous practical application possibilities (this effect leads
to substantial changes in solubility rates of chalcogenide
layer, which makes possible the production of various
relief images) were shown for microelectronics [2-3], op-
tical memory [4], holography, diffractive optics [5-9], etc.
Many publications were devoted to the investigation of
the photodoping mechanism and the basic physical prop-
erties of this phenomenon [10-18]. However, the peculiari-
ties of the interaction of metal atoms with the atoms of the
chalcogenide matrix, along with the local structure of such
products, have been studied very little even for the most
investigated As3S3-Ag structure. This is associated with
experimental difficulties while using the standard X-ray
methods of investigations. Application of the optical non-
destructive techniques (including the investigations of the
Raman spectra ) can bring information on the changing of
chemical bonds and the molecular structure for the ChVS
films as a result of photodoping.
It is known that some metals intensively undergo
photodoping in the structures based on vitreous arsenic sul-
fide and arsenic selenide . Investigations of the local struc-
ture of photodoped As-S layers were carried out using Ra-
man scattering [11-14]. It was found that, in general, Raman
spectra in such films are analogous to those for the As-S-Ag
massive glasses and indicate the presence of Ag-S bonds.
The latter are analogous to those present in Ag2S compounds
[11-12]. Later studies [13-14] conducted gave more detailed
features of the possible formation mechanisms involving
metal-impurity chemical bonds with the As2S3 glass matrix,
and of the influence of impurity on the glass structure, too
.The structure of the photodoped As-Se layers is less inves-
tigated. In the present work, the results of the Raman spec-
tra investigations of ChVS (As40S60, As40Se60, As40S40Se20
compositions) and their modifications with photodoping by
A. V. Stronski et al.: Raman spectra of Ag- and Cu- photodoped...
64 SQO, 2(2), 1999
Ag or Cu are presented and discussed. The peculiarities of
the formation of the metal-chalcogenide bonds are discussed.
2. Experiment
The bulk materials (As40S60-xSex, x = 0; 20; 60) were pre-
pared by the direct synthesis from 5N purity elements in
evacuated quartz ampoules at 700 - 750 oC for 8 - 24 hrs.
After synthesis , the ampoules were quenched in cold
water. Thin ChVS films (d = 0.4-5 µm) and metal (Ag,Cu
with d = 0.01-0.2 µm) were sequentially deposited by the
vacuum thermal evaporation (p = 1.33×10-3 Pa) from
the resistance-heated quartz or Mo boats onto clean glass
substrates (microscopic slides) kept under room temper-
ature. Deposition rate was continuously measured using
the quartz microbalance technique, and in the present
study it was within 1 - 6.0 nm/s. The prepared two-layer
ChVS-metal structures were exposed to light in order to
photodissolve and uniformly spread the metal in the
ChVS film. An incandescent lamp was used for expo-
sure. The concentrations of the metal in the photodoped
samples were determined by the mass proportion of the
deposited metal and ChVS. The metal concentration in-
tervals for the investigated samples were chosen by tak-
ing into account the photodoping peculiarities in such
structures.
The Raman spectroscopy investigations were carried
out by using BRUKER IFS55 IR spectrophotometer
with a FRA 106 accessory. The laser irradiation on the wave-
length 1,06 µm was used for the excitation of the Raman
spectra. In our case , this wavelength value was very essen-
tial because irradiation of samples in this range causes no
detectable photostructural transformations or photodoping
processes.
3. Results
Raman spectra of the investigated materials are presented
in Fig.1-3. For each of the investigated compositions
(As40S60, As40Se60,and As40S40Se20) the spectra of the mas-
sive glass, the thermally- evaporated film and the photodoped
film are presented. While normalizing on the intensity max-
imum, a correlation is observed in the spectral position and
form of the most intense main bands of the thermally depos-
ited film and the corresponding massive glass. This indi-
cates the presence of the same structural elements in them,
which determines the scattering characteristics in the spec-
tra of both the massive glass and the film. However, at the
same time, differences are also observed between these two
types of spectra. In general, they are characterized by the
appearance of the additional weak bands in the spectra of
the films. This difference is more pronounced for As40S60
and less for As40Se60.
In the spectrum of the thermally evaporated As40S60 film
the number of bands is equal to 14 (see Fig.1, curve 3), which
corresponds to the results obtained in an earlier investiga-
tion [19]. In the region of the main maximum at 345 cm-1
the splitting can be seen, which is absent in the spectrum of
the massive glass. From the results of previously carried out
investigations [20-21], it is known that these differences as
well as the numerous weak bands in the 50-250 cm-1 range,
and also the band near 495 cm-1, are due to the presence of
non-stoichiometric structural units of As4S4 and S2 in the
structural network of the thermally-evaporated As40S60 film.
The main maximum in the spectrum of the photodoped
layer in relation to the maximum for the initial nondoped
layer is shifted to higher wavenumber, namely to 373 cm-1
(see Fig.1, curve 4). The spectrum of the photodoped layer
is also characterized by the presence of a second intensive
Fig. 1. Raman spectra of As40S60: 1 � bulk glass ; 2 � As40S60 layers annealed in Ar atmosphere; 3 � as-evaporated As40S60 layer; 4 � As40S60 layer
photodoped with Ag (As2S3Ag2.2).
100 200 300 400 500 600
0
2
4
6
~
343
145
186
217
270
373
363
345
234
223191
169
136
495
4
3
2
1
I,
a
rb
.
u
n
.
λ , cm
-1
A. V. Stronski et al.: Raman spectra of Ag- and Cu- photodoped...
65SQO, 2(2), 1999
band near 217 cm-1. The wavenumber position of several
bands and shoulders in this spectrum, in 50-190 cm-1 range
is near to the position of the weak bands in the spectrum of
the thermally-evaporated As40S60 film. It is necessary to
mention here that under the annealing ( see Fig.1, curve 2)
or the exposure processes of As40S60 films there is no sig-
nificant change of the main maxima position, and the corre-
sponding spectra approach the spectrum of massive glass
(see Fig.1, curve 1). The polymerization that proceeds un-
der the exposure or annealing of As40S60 films decreases
the number of the nonstoichiometric structural units As4S4
and S2 , that leads to the sufficient intensity decrease of cor-
responding to them weak bands in the 50-250 cm-1 range,
and also of the band near 495 cm-1. It can be seen from the
comparison of curves 1-3 that the result involving only po-
lymerization processes (see curve 2) is sufficiently differ-
ent from the changes observed after photodoping processes
(see curve 4), where the polymerization processes and pho-
tostimulated introduction of silver proceed simultaneously.
In the spectrum of thermally-evaporated As40Se60 layer
the band position of the most intense band is near 224 cm-1
(see Fig.2, curve 2), that practically coincides with the po-
sition of the maximum in spectrum for massive glass with
the same composition. The maximum in the spectrum of
the As40Se60 layer photodoped by silver (see curve 3) is
situated practically at the same wavenumber. In the spec-
trum of the thermally-evaporated As40Se60 film the asym-
metry of the main band and the presence of weak bands in
the region 50-175 cm-1 can be seen. Such differences in
spectra of the film and massive glass As40Se60 are explained
by the presence in the films network of the nonstoichiomet-
ric structural elements, similar to those that are present in
the network of the arsenic sulfide layers [20]. As a result of
the photodoping of As40Se60 with silver, the intensity of the
scattering in the wavenumber region less then 175 cm-1 is
increased in a such way that the weak bands which are char-
acteristic for the As40Se60 film are not seen (see Fig. 2, curve
3), new maxima are not observed.
The most intensive bands in the Raman spectra of
thermally-evaporated As40S40Se20 layers are located near
222 and 343 cm-1 (see Fig. 3, curve 2) which are near to
the band maxima positions in the spectra of the layers
for the extreme compositions (As2S3 and As2Se3). The
differences in the spectra of massive As40S40Se20 glass
from the spectra of the layers in general are in agree-
ment to those that were observed in the spectra of As2S3
and As2Se3 layers in relation to their corresponding
massive glasses. As a result of photodoping of As40S40Se20
by silver up to the ∼ 25 at% concentration the band maxima
positions (222 and 343 cm-1 ) are shifted to the high wave-
number region up to 234 and 353 cm-1, respectively (see
Fig. 3, curve 4). Curve 3 of the same figure corresponds to
the sample involving photodoping of the As40S40Se20 film
up to ~ 10 at% Photodoping of the As40S40Se20 layers by
copper also causes the shift of the maxima to 232 and
352 cm-1 , respectively (see Fig. 3 curve 5). In all spectra
for As40S40Se20 layers photodoped by metals, the wave-
number positions of the shoulders near 188, 146, 135 cm-1
coincide with the positions of the corresponding weak bands
in the spectra of the initial layers.
4. Discussion
The vibrational spectra of the chalcogenide glasses show
differences with respect to other amorphous materials.
The influence of the matrix elements that modulate the
density of the phonon states is more strongly pronounced. In
this connection, the main peculiarities of the Raman spectra
of the arsenic-containing ChVS are in agreement with the
molecular selection rules for the AsX3 (X = S, Se) pyrami-
dal structural units in the glass [22-25]. The most intense
bands in the Raman spectra of As2S3 and As2Se3 occur near
345 cm-1 and 224 cm-1 and correspond to the ν1(A) valence
vibrations of the corresponding pyramidal structural units in
the glass. The deformation vibrations ν3(E) near 310 cm-1
for As2S3 and 216 cm-1 for As2Se3 are pronounced weaker.
The stretching and compression force constant Kr of As-X
Fig. 2. Raman spectra of As40Se60: 1 � bulk glass ; 2 � as-evaporated
As40Se60 layer; 3 � As40Se60 layer photodoped with Ag (~ 10 at%).
100 200 300 400 500 600
0
1
2
3
4
5
6
~
234
348
352
232
234
353
253
348
146
135 188
201
360
343
257
222
5
4
3
2
1
I,
a
rb
.
u
n
.
λ, cm
-1
100 200 300 400 500 600
0
2
4
6
8
10
12
~
159
137
148
170
112
224
3
1
2
I,
a
rb
.
u
n
.
λ, cm
-1
Fig. 3. Raman spectra of As40S40Se20 layers: 1 � bulk glass ; 2 � asevapo-
rated As40S40Se20 layer; 3, 4 � photodoped with Ag ~ 10 and 25 at%,
respectively; 5 � photodoped with Cu.
A. V. Stronski et al.: Raman spectra of Ag- and Cu- photodoped...
66 SQO, 2(2), 1999
bond that determine the wavenumber of the valence vibra-
tions can be calculated according to the Gordy rule [23, 26]:
Kr = aN(XAsXx/d2)3/4 + b, ( 1 )
where a and b are empirical constants, N is the order of the
bond, XAs and Xx are the electronegativities of the corre-
sponding elements, and d is the bond length.
As mentioned above, the introduction of metals into
the As40S60 and As40S40Se20 layers causes the shift of
the Raman maxima to the region of higher wavenum-
bers. The wavenumber position for the maximum of the
photodoped As40Se60 spectrum remains the same as for
the initial nondoped layer.
It is important to note that such changes in the Ra-
man spectra for the As40S60 and As40S40Se20 layers or
the absence of essential changes for the As40Se60 layers
are characteristic for the photodoped ChVS layers with
the substantial dopant concentration, when the number
of the metal atoms is near to the number of chalcogene at-
oms and for some concentrations exceeds the number of pnic-
tide atoms. For example, the optimal concentration of Ag dur-
ing photodoping of the As2S3 layers is 30-32 at%, which cor-
respond to the composition As2S3Ag2.2-2.4 [27]. Thus, the
given set of experimental results can be explained by the
formation of specific bonds between the metal and the chal-
cogen atoms. In the given case, the same principle acts, which
explains the weak influence of some dopants on the ChVS
electrophysical properties and when the valence demands
of the dopant are satisfied at the cost of lone pair electrons
[28].
It was shown that the metal with V valence in the ChVS
melt forms V normal covalent bonds in the place of broken
bonds and 4 - V coordinative bonds formed with the partic-
ipation of the lone pair electrons from chalcogene atoms [
29-30]. In the network structure of the thermally- evaporat-
ed film of As2SxSe3-x composition, the number of broken
bonds can exceed 7 at % [31]. Thus, a certain amount of
metal atoms can be bonded by means of normal covalent
bonds. The presence of the intense band in the spectrum of
the photodoped layer near 217 cm-1 supports this sugges-
tion. The presence of several shoulders in the region 50-
260 cm-1 in the spectrum of thermally-evaporated As40S60
layers, whose wavenumber positions correspond to the po-
sitions of weak bands, which are connected to As-As vibra-
tions, indicate that the covalent pnictide bonds (As-As) also
contribute to this part of spectrum. The band near 495 cm-1
which indicate the presence of the non-stoichiometric struc-
tural units S2 in the photodoped As40S60 layer is absent. This
can be explained by sulfur bonding with metal during
photodoping processes (normal covalent bonds) and also
by the polymerization . Illumination induces polymeriza-
tion processes between the S-rich and As-rich parts of the
films, resulting in formation of As2S3 network structure. The
content of these molecular fragments is decreased because
of these reactions.
As said above, the polymerization processes and photo-
stimulated introduction of silver proceed simultaneously.
Nevertheless , the other metal atoms satisfy the demands of
their chemical valency at the cost of coordinative bonds for-
mation. In accordance with the nature of such bonds after
their formation there is no destruction of pyramidal struc-
tural units of As-S-Se glasses, that is in agreement with pres-
ervation of the main bands characteristic for the undoped
samples in the Raman spectra of the investigated photodoped
As-S-Se layers. Sulfur-silver coordinative bonds also con-
tribute to the band at 217 cm-1. Under formation of the co-
ordinative bonds metal-chalcogene, partial redistribution of
the charge density of the lone-pair electrons from the chal-
cogene to metal atom occurs. Due to this, the effective elec-
tronegativity of the chalcogene increases, which in accor-
dance with the Gordy rule leads to an increase of the force
constant Kr. This force constant change is observed in the
Raman spectra of As2S3 as the shift of the maximum to the
higher wavenumber side.
The absence of shift of the maximum in the Raman
spectra of photodoped As2Se3 can be explained in the
following way. The atomic mass is more than two times
bigger for selenium than for the sulphur. Thus, under
the same relative increase of the force constant the effect
of the redistribution of the density of phonon states must
be less pronounced. One the essential reason more for
the observed differences in the spectra of As2S3 and As2Se3,
can be the smaller metal concentration up to which the ar-
senic selenide is photodoped.
In the investigations of the IR spectra of GeSe2 and
As2Se3 photodoped by metals the displacement of the
density of phonon states to the high wavenumber side
(that was characteristic for As2S3 and GeS2 [32]) was not
observed. This experimental results shows that under the
formation of the coordinative metal-selenium bonds, the
charge transfer is less pronounced, then for the metal-
sulphur bonds. Also, it is known, that Ag-S (Ag-Se)
bonds which form the Ag2S(Se) structure have weak
cross-sections of Raman scattering [12]. Therefore, a
substantial amount of Ag-Se bonds in As2Se3Agx prod-
ucts will be hardly observed in Raman spectra. Besides
that, it can be seen from the comparison of the spectra
of thermally evaporated As2S3 and As2Se3 films that the
bands corresponding to the presence of the homopolar
bonds are sufficiently weaker in the Raman spectrum of
As2Se3 film. Thus, they are also hardly observed in the
Raman spectrum of photodoped As2Se3 layer.
In the network structure of the As-S-Se glasses, the
chaotic replacement of chalcogenes of one type by chalco-
genes of another type takes place [33-34]. This can explain
why the displacement value of the main maxima in the Ra-
man spectra of the As40S40Se20 layer photodoped by silver
or copper has an intermediate magnitude between those ob-
served for the two extreme stoichiometric compositions. It
is necessary to note here that in the region of main band
234 cm-1 in the Raman spectra of the As40S40Se20 layer
photodoped by silver the weak bands, corresponding to the
presence of the As4S4 and S2 nonstoichiometric structural
units within the films network (see Fig.1, curve 3) are also
present. This circumstance makes clouds the interpretation
of its evolution. In the spectrum of As40S40Se20 layer
photodoped by silver up to the 25 at% the intensity ratio
between the bands at 234 and 353 cm-1 is preserved the same
A. V. Stronski et al.: Raman spectra of Ag- and Cu- photodoped...
67SQO, 2(2), 1999
as in the spectrum of the nondoped layer involving the bands
at 222 and 343 cm-1. Taking into account the results of the
previous investigations of the IR absorption spectra of the
photodoped As2S3 layers [35], we can consider these ex-
perimental data to be good evidence that during the
photodoping of the As2SxSe3-x compositions, no destruc-
tion of the pyramidal structural units in films takes place.
The main mechanism, that enables the structural elements
of chalcogenide glasses to remain indestructible under the
photodoping by the metals is that the lone-pair electrons of
the chalcogene atoms are not taking part in the formation of
the AsX3 pyramids. Usually, the coordinative bonds are
weaker than covalent ones [36]. Thus, the formation of the
coordinative metal-chalcogene bonds doesn�t lead to the
destruction of the structural units of the glass, and can in-
fluence only the dynamical characteristics of this structural
elements. Under the formation of such bonds during the
photodoping process or processes of the photostimulated
mass transfer of metal through the photodoped layer, the
ions of metal are diffuse along the sites of the lone-pair elec-
trons belonging to the chalcogene atoms. The formation of
the normal metal-chalcogene covalent bonds occurs by
means of metal diffusion on the sites of defects of the amor-
phous matrix. Two types of metal photodiffusion channels
correspond to two types of the structural centers [35], and
presence of the different activation energy values for the
silver photostimulated diffusion into ChVS during the var-
ious stages of the process [15, 37] supports this suggestion.
5. Conclusion
The study of Raman spectra of Ag- and Cu- photodoped
chalcogenide films revealed that changes in the Raman
spectra with photodoping by Ag or Cu are consistent
with the suppositions concerning normal covalent and
coordinative bond formation between metal additives
and chalcogen atoms. Such behaviour is in accordance
with the principle, which explains the slight influence of
the additives on the electrical properties of chalcogenide
glasses, when valence demands of additive atoms are satis-
fied at the cost of lone-pair electrons. The introduction of a
high concentration (10-30 at%) of doping metal in As40S60-
xSex does not lead to destruction of a large fraction of struc-
tural unit bonds.
Acknowledgements
The authors wish to express their gratitude to Prof. I. Z. In-
dutnyi and Dr. A. A. Kudryavtsev for valuable discussion
and critical reading the manuscript.
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