Optical and structural properties of Ag(Cu)–As
2
Se
3
chalcogenide films prepared by a photodoping
Kazuhiko Ogusu
a,
*
, Shinpei Maeda
a
, Michihiko Kitao
b
,
Honpu Li
a
, Makoto Minakata
b
a
Department of Electrical and Electronic Engineering, Shizuoka University, 3-5-1, Johoku, Hamamatsu 432-8561, Japan
b
Research Institute of Electronics, Shizuoka University, 3-5-1, Johoku, Hamamatsu 432-8011, Japan
Received 28 April 2004; received in revised form 10 June 2004
Available online 13 October 2004
Abstract
We prepared Ag(Cu)–As
2
Se
3
films by step-by-step photodoping Ag (or Cu) into an evaporated As
2
Se
3
film and determined their
optical properties such as refractive index and band gap energy from the transmission spectrum of the sample. The highest concen-
tration of the metal doped into the amorphous As
2
Se
3
film was 21 at.% for Ag and 7 at.% for Cu. Moreover we performed Raman
spectroscopy to obtain information about the local structure of the photodoped chalcogenide films. It has been found that there is a
distinct difference in the optical properties between Ag–As
2
Se
3
and Cu–As
2
Se
3
films. The measured Raman spectra agree approx-
imately with ones we previously obtained for bulk glasses. In our case, this agreement means that the successive photodoping used
here produces nearly homogeneous chalcogenide films. It has also been found that a mixture of Se clusters (Se
8
ring, Se
12
ring, and
Se
4
chain) is formed near the surface of the photodoped Ag(Cu)–As
2
Se
3
films.
Ó 2004 Elsevier B.V. All rights reserved.
PACS: 42.70.Ce; 68.55.Lm; 78.30.Ly; 78.66.Jg
1. Introduction
Chalcogenide glasses based on S, Se, and Te have
many unique optical properties, which can be used for
a variety of applications [1]. These glasses are very
promising materials for use in fiber optics and guided-
wave devices in integrated optics since they exhibit a
good transparency in the infrared region, especially at
the telecommunicati on wavelengths of 1.3 and 1.55 lm
[2]. Moreover, chalcogenide glasses posses a high
third-order non-linearity with an ultrafast time response
[1,3–6]. The non-linear refractive index n
2
of Se-based
chalcogenide glasses is generally higher than that of S-
based glasses since the high non-linear refractive indices
are expected for glasses with high linear refractive indi-
ces, i.e., glasses composed of heavy elements. We re-
cently developed Ag–As
2
Se
3
(i.e., Ag
x
(As
0.4
Se
0.6
)
100x
)
glasses with n
2
greater than 2000 times that of fused sil-
ica by the addition of Ag into As
2
Se
3
glasses [7]. We ex-
pect that such non-linear glasses are promising mate rials
for all-optical switching devices at the telecommunica-
tion wavelengths. In order to implement non-linear
guided-wave devices, it is necessary first to fabricate
waveguides with such non-linear materials. Although
the most standard fabrication method of planar wave-
guides (i.e., thin films) is vacuum evaporation, one can-
not directly prepare Ag–As–Se films out of original
ternary glasses by the evaporation method because of
their phase separation. One way for overcoming this
problem is the photo-induced diffusion of metals into
chalcogenide thin films call ed photodoping [8–11]. This
process is understood as a kind of phot oelectro-chemical
0022-3093/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jnoncrysol.2004.08.239
*
Corresponding author. Tel./fax: +81 53 478 1089.
E-mail address: tekogus@ipc.shizuoka.ac.jp (K. Ogusu).
www.elsevier.com/locate/jnoncrysol
Journal of Non-Crystalline Solids 347 (2004) 159–165