Long-wave light sensitivity of a thin film system based on PbI₂ and Cu
Photostimulated interaction in a sandwich-like thin film system based on PbI₂ and Cu (photodoping effect) makes it possible to use the system as a recording medium. On the other hand, since the layer consisting of copper nanoparticles embedded into the PbI₂ matrix is formed as a result of photodisso...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
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irk-123456789-1212762017-06-14T03:07:42Z Long-wave light sensitivity of a thin film system based on PbI₂ and Cu Sopinskyy, M.V. Mynko, V.I. Olkhovik, G.P. Photostimulated interaction in a sandwich-like thin film system based on PbI₂ and Cu (photodoping effect) makes it possible to use the system as a recording medium. On the other hand, since the layer consisting of copper nanoparticles embedded into the PbI₂ matrix is formed as a result of photodissolution of Cu film, this effect can be considered as an original way to produce nanocomposites. In this work, long-wave sensitivity of the PbI₂–Cu₂O–Cu system has been studied in conjunction with the structure of the PbI₂ film. It has been established that, in the hν < Eg (PbI₂) spectral region the light absorption in PbI₂ film and the metal film photodissolution rate are higher for the less compact (more porous) PbI₂ films. 2015 Article Long-wave light sensitivity of a thin film system based on PbI₂ and Cu / M.V. Sopinskyy, V.I. Mynko, G.P. Olkhovik // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2015. — Т. 18, № 4. — С. 460-463. — Бібліогр.: 17 назв. — англ. 1560-8034 DOI: 10.15407/spqeo18.04.460 PACS 78.20.Ci, 78.20.-c http://dspace.nbuv.gov.ua/handle/123456789/121276 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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Photostimulated interaction in a sandwich-like thin film system based on PbI₂ and Cu (photodoping effect) makes it possible to use the system as a recording medium. On the other hand, since the layer consisting of copper nanoparticles embedded into the PbI₂ matrix is formed as a result of photodissolution of Cu film, this effect can be considered as an original way to produce nanocomposites. In this work, long-wave sensitivity of the PbI₂–Cu₂O–Cu system has been studied in conjunction with the structure of the PbI₂ film. It has been established that, in the hν < Eg (PbI₂) spectral region the light absorption in PbI₂ film and the metal film photodissolution rate are higher for the less compact (more porous) PbI₂ films. |
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Sopinskyy, M.V. Mynko, V.I. Olkhovik, G.P. |
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Sopinskyy, M.V. Mynko, V.I. Olkhovik, G.P. Long-wave light sensitivity of a thin film system based on PbI₂ and Cu Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Sopinskyy, M.V. Mynko, V.I. Olkhovik, G.P. |
| author_sort |
Sopinskyy, M.V. |
| title |
Long-wave light sensitivity of a thin film system based on PbI₂ and Cu |
| title_short |
Long-wave light sensitivity of a thin film system based on PbI₂ and Cu |
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Long-wave light sensitivity of a thin film system based on PbI₂ and Cu |
| title_fullStr |
Long-wave light sensitivity of a thin film system based on PbI₂ and Cu |
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Long-wave light sensitivity of a thin film system based on PbI₂ and Cu |
| title_sort |
long-wave light sensitivity of a thin film system based on pbi₂ and cu |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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2015 |
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http://dspace.nbuv.gov.ua/handle/123456789/121276 |
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Long-wave light sensitivity of a thin film system based on PbI₂ and Cu / M.V. Sopinskyy, V.I. Mynko, G.P. Olkhovik // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2015. — Т. 18, № 4. — С. 460-463. — Бібліогр.: 17 назв. — англ. |
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Semiconductor Physics Quantum Electronics & Optoelectronics |
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| first_indexed |
2025-07-08T19:31:02Z |
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2025-07-08T19:31:02Z |
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1837108367539044352 |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2015. V. 18, N 4. P. 460-463.
doi: 10.15407/spqeo18.04.460
© 2015, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
460
PACS 78.20.Ci, 78.20.-c
Long-wave light sensitivity of a thin film system
based on PbI2 and Cu
M.V. Sopinskyy, V.I. Mynko, G.P. Olkhovik
V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
45, prospect Nauky, 03028 Kyiv, Ukraine
Abstract. Photostimulated interaction in a sandwich-like thin film system based on PbI2
and Cu (photodoping effect) makes it possible to use the system as a recording medium.
On the other hand, since the layer consisting of copper nanoparticles embedded into the
PbI2 matrix is formed as a result of photodissolution of Cu film, this effect can be
considered as an original way to produce nanocomposites. In this work, long-wave
sensitivity of the PbI2–Cu2O–Cu system has been studied in conjunction with the
structure of the PbI2 film. It has been established that, in the h < Eg (PbI2) spectral
region the light absorption in PbI2 film and the metal film photodissolution rate are
higher for the less compact (more porous) PbI2 films.
Keywords: photodoping, nanoparticles, nanocomposite, inorganic photoresist, thin film,
copper, lead iodide, Wemple and DiDomenico single-oscillator model.
Manuscript received 12.05.15; revised version received 05.08.15; accepted for
publication 28.10.15; published online 03.12.15.
1. Introduction
Investigation of the effect of photostimulated interaction
in semiconductor-metal systems (photodoping effect) is
of a considerable scientific and practical interest [1, 2]. It
is important part of fundamental physics of low-energy
radiation influence on thin-film systems and impurities
in solids. The effect was the basis in creation of specific
recording media used as a high-resolution inorganic
resist in electronics, optics, and as a medium for
holography, data recording, etc. The best results in many
applications have been achieved for the chalcogenide
glassy semiconductor (ChGS) – Ag systems [1, 2].
The competitive silver-free PbI2–Cu2O–Cu
recording medium was suggested in [3-5]. Its charac-
teristics (sensitivity, resolution, stability) approach to
those of the ChGS–Ag based media. It was achieved
primarily due to controlled formation of the PbI2–Cu
interface. Comprehensive study of the interaction
between PbI2 and Cu films stimulated by light from
the lead iodide fundamental absorption band allowed us
to create the model of photodoping effect for this
case [3, 4]. Based on this, the high-quality photo-
lithography technology for the practically important
metals and metalloceramics (Cr, Mo, W, Al, Cr-SiO,
etc.) using PbI2–Cu2O–Cu photoresist system was also
suggested [6].
An important feature of the PbI2–metal based
systems is that, unlike the ChGS – metal based systems,
their light-generated photodoped layer is heterogeneous
and consists of metal nanoparticles embedded in the
polycrystalline PbI2 matrix. The study of objects
containing metal nanoparticles has considerable
independent significance. Therefore, in view of its
importance, the study of photostimulated interaction in
the PbI2–Me light-sensitive systems should be viewed in
a broader context than just the study of these systems as
a recording medium. In the papers [7, 8], we have shown
that varying such parameters of deposition process as
residual pressure in vacuum chamber Pdep and deposition
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2015. V. 18, N 4. P. 460-463.
doi: 10.15407/spqeo18.04.460
© 2015, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
461
rate Vdep has an essential effect on the structure of
vacuum-deposited lead iodide films. By changing the
structure of halide film, we were able to a certain extent
control concentration, size and shape of copper nano-
particles in photodoped nc-Cu–PbI2 layers obtained
by exposition of PbI2–Cu2O–Cu system with the h >
Eg (PbI2) light [7, 8].
At the same time, interaction under the influence of
long-wave light (h < Eg (PbI2)) is less studied and
understood. Meanwhile, some interesting practical
results using such light have been obtained. In [9], the
full color and/or dichroic recording process was
implemented under exposing the PbI2–Me systems with
the island metal film by the h < Eg (PbI2) light. Authors
[10, 11] created nc-Ag–PbI2 and nc-Cu–PbI2 nano-
composites from layered Ag–PbI2 and Cu–PbI2 systems
using the h > Eg (PbI2) unpolarized light. Then they
exposed it to the linearly polarized h < Eg (PbI2) light.
As a result, the periodic diffraction structures consisting
of the metal nanoparticle rows oriented in parallel to the
electric vector of exposing light were formed. This paper
presents the results of studying the spectral dependences
of the light-sensitivity for PbI2–Cu2O–Cu systems under
action of light with quanta energy h < Eg (PbI2). Special
attention was given to studying the influence of
semiconductor film preparation conditions on the long-
wave sensitivity of these systems.
2. Experimental procedure and results
The sandwich-like samples of PbI2–Cu2O–Cu systems
and companion PbI2 films on K-8 glass substrates were
prepared as described in [3, 4]. At first, the copper film
was deposited at the pressure in the vacuum chamber
Pdep = 3·10–3 Pa with the deposition rate Vdep = 1.0 nm/s.
Then, the Cu2O film was formed on this film by
oxidation of Cu film in air. This step is necessary to
obtain highly sensitive reproducible systems [3, 4].
Finally, the PbI2 film was deposited. In various vacuum
cyсles the Vdep amounted between 0.1 and 1 nm/s, and
Pdep between 3.0·10–3 Pa and 1.5·10–2 Pa. This process
produced the PbI2–Cu2O–Cu samples in which the Cu
and Cu2O films had identical characteristics, while
characteristics of the PbI2 film varied from sample to
sample. The thicknesses of the PbI2, Cu2O, and Cu films
were 50, 4, and 40 nm, respectively.
The systems were exposed by light from the
spectral region h=1.77…2.3 eV (Eg(PbI2)≈ 2.3…2.4 eV
for thin films of lead iodide at room temperature [12-
15]). The metal film expenditure kinetics during
irradiation was monitored using photometry: changes in
the transmission coefficient T were measured at =
1500 nm, and light sensitivity S was in proportion to the
rate of its change.
The optical techniques (ellipsometry and photo-
metry R-T technique) were used to obtain structural
information of the PbI2 films. The thickness and optical
constants of the as-deposited PbI2 films were determined
using ellipsometric measurements at the wavelength
633 nm. The KSVU-23 spectral complex and calculation
method described in [16] were used to determine the
spectral dependences of the refractive index n and ab-
sorption index k for the PbI2 films in the 400…1000 nm
range.
As it was demonstrated using measurements of the
PbI2 films density and investigations of n(hν), k(hν)
dependences in the h > Eg (PbI2) spectral region [7, 8],
the greater the deposition rate and especially the residual
pressure during the deposition of PbI2 films, the less
dense and more disordered films are formed. Fig. 1
shows the spectral dependences of light-sensitivity S for
two systems with the identical Cu and Cu2O films but
with differently deposited PbI2 films. (The figure shows
the data for the systems in which the properties of PbI2
films differ the most among the investigated set of
samples.) The PbI2 film deposited at Vdep = 1.0 nm/s, Pdep
= 3.0·10–3 Pa has n (λ = 633 nm) = 2.84, and the PbI2
film deposited at Vdep = 1.0 nm/s, Pdep = 1.5·10
–2
Pa has
n (λ = 633 nm) = 2.52. The estimated values of porosity
consists 0.05 and 0.23, respectively. As can be seen, the
sensitivity for the system with less dense PbI2 film is
sufficiently (several times) higher. For both systems, the
edge of the sensitivity spectrum is satisfactory described
with S ~ (h – h0)
2 quadratic dependence, which is
analogous to the Fowler dependence for internal photo-
emission of charge carriers from metal into semi-
conductor. The S(h) dependence of the same kind was
obtained in PbI2–Cu system without an intermediate
oxide layer [1]. The h0 = 1.69 eV value obtained here
for the system with intermediate oxide layer and dense
PbI2 film is quiter close to the h0 = 1.65 eV value [1]
obtained for the PbI2–Cu system without an intermediate
oxide layer. Substitution of the dense PbI2 film with the
porous one lowers the h0 value at ~0.4 eV. In [1], it was
assumed that the S ~ (h – h0)
2 spectral dependence in
the long-wave range of the spectrum is determined by
photoemission from metal, which leads to changes in the
electric field at the contact and to the transfer of the
metal ions. In this case, the h0 value can be regarded as
the height of the barrier for internal photoemission for
metal–semiconductor contact. We also may assume that
in the case of the PbI2–Cu2O–Cu systems the spectral
course of the sensitivity is determined by the internal
photoemission of charge carriers from metallic film.
To clarify the question of the difference among the
long-wave sensitivity characteristics of the PbI2–Cu2O–
Cu systems with different PbI2 films, we additionally
investigated the dispersion of refractive index n within
this spectral region for the PbI2 films deposited at
various sets of the deposition process parameters. This is
particularly useful in the spectral region where the
values of the absorption index are small and difficult to
measure, especially at low film thickness. Besides this
technical difficulty in determining the small values of
absorption index, there is also the methodological
difficulty. Methodological circumstances are as follows:
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2015. V. 18, N 4. P. 460-463.
doi: 10.15407/spqeo18.04.460
© 2015, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
462
in the presence of scattering (which is always inherent in
varying degrees in all the samples) the photometric
measurements based on the transmitted light intensity
determination actually obtain the value of extinction
index that contains the components of the absorption and
scattering. Thus, the smaller the true value of the
absorption index, the greater the relative contribution of
the scattering in the measured value of the extinction
index.
The refractive index dispersion data below the
interband absorption band of many covalent and ionic
compounds is rather well described by the Wemple and
DiDomenico single-effective-oscillator model with two
parameters E0 and Ed [17]:
22
0
02
)(
1)(
hE
EE
hn d . (1)
1.2 1.4 1.6 1.8 2.0 2.2
0.0
0.5
1.0
1.5
2.0
2.5
S
1
/2
,
ar
b
.
u
n
it
s
heV
Fig. 1. Spectral dependences of light sensitivity (S) in spectral
region hν < Eg (PbI2) for PbI2–Cu2O–Cu system in which PbI2
film is deposited at Pdep = 3.0·10–3 Pa, Vdep = 1 nm/s (triangles)
and Pdep = 1.5·10–2 Pa, Vdep = 1 nm/s (circles).
0 1 2 3 4 5 6
0.12
0.15
0.18
0.21
0.24
1
/(
n
2
-1
)
(h
eV
Fig. 2. Description of the refractive index dispersion on the
basis of the Wemple and DiDomenico single-oscillator model.
PbI2 film is deposited at Pdep = 3.0·10
–3 Pa, Vdep = 1 nm/s
(triangles) and Pdep = 1.5·10
–2 Pa, Vdep = 1 nm/s (circles).
The parameter Ed is the oscillator strength or
dispersion energy which is a measure of the strength of
interband optical transitions. The oscillator energy E0 is
the average energy gap. To establish how well the
dispersion of our PbI2 films is simulated by the Wemple
and DiDomenico single-oscillator model, we plotted
dispersive n(h) dependence as 1/(n2 – 1) versus h. The
experimental values for the PbI2 films with estimated
porosity p of 0.05 and 0.23 are given in Fig. 2 by circles
and triangles. The value of E0 and Ed can be directly
determined from the slope (E0Ed)
–1 and the intercept on
the vertical axis (Ed /E0). These values are Ed = 20.14 eV,
E0 = 4.04 eV for the most dense film, Ed = 15.1 eV, E0 =
3.86 eV for the least dense film. As seen, for the film
with p ≈ 0.05 good description by the dependence (1)
occurs at h ≤ 2.2 eV, and for the film with p ≈ 0.23 at
h ≤ 2.0 eV. Thus, the more porous and disordered PbI2
film is, the longer are the wavelengths at which
deviation of the films’ refractive index dispersion from
the Wemple and DiDomenico single-oscillator model
starts. This indicates that in less compact PbI2 film the
increase of absorption starts at lower photon energies.
That is, in these films the tail of absorption spectrum is
more extended (and definitely greater in magnitude).
The growth of this long-wave absorption is due to the
increased density of states in the band gap due to the
increase in the number of structural defects and
impurities in the less compact halide films. As seen, the
increase in the number of the gap states also reduces the
value of the average energy gap parameter E0.
3. Conclusions
The less dense PbI2 films deposited at higher pressure
and at greater deposition rate show more pronounced
deviation of the refractive index dispersion in the h <
Eg (PbI2) region from the Wemple and DiDomenico
single-oscillator model. The most probable cause for this
phenomenon is stronger absorption in this spectral
region due to the greater structural and compositional
disordering in those films.
There is correlation between the PbI2 film n(h)
dispersion curves in the h < Eg(PbI2) region and the
long-wave sensitivity of the PbI2–Cu2O–Cu systems –
the more pronounced is deviation, the higher is the
sensitivity.
These results show that the energy states in the
band gap of halide semiconductor play significant role in
the long-wave light sensitivity of the thin film systems
based on lead iodide and copper.
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Semiconductor Physics, Quantum Electronics & Optoelectronics, 2015. V. 18, N 4. P. 460-463.
doi: 10.15407/spqeo18.04.460
© 2015, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
463
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