DOI: 10.1007/s00339-002-1951-1
Appl. Phys. A 76, 969–973 (2003)
Rapid communication
Materials Science & Processing
Applied Physics A
c.h. chen
✉
t. kiguchi
a. saiki
n. wakiya
k. shinozaki
n. mizutani
Characterization of defect type and
dislocation density in double oxide
heteroepitaxial CeO
2
/YSZ/Si(001) films
Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology,
2-12-1 O-okayama, Meguro-ku, Tokyo 152-8552, Japan
Received: 12 August 2002/Accepted: 14 August 2002
Published online: 4 December 2002 • © Springer-Verlag 2002
ABSTRACT
In order to qualitatively and quantitatively analyze the structural defects
including the defect types and their concentrations in oxide heteroepitaxial films,
a new X-ray rocking-curve width-fitting method was used in the case of double
CeO
2
/YSZ/Si (YSZ = yttria-stabilized ZrO
2
) films that were prepared by pulsed
laser deposition. Two main defect types, angular rotation and oriented curvature, were
found in both CeO
2
and YSZ. Dislocation densities of CeO
2
and YSZ, which were
obtained from the angular rotations, are functions of the YSZ thickness. A distinct
two-step correlation between dislocation densities of CeO
2
and YSZ was found that as
the dislocation density of YSZ is higher than 2.4 × 10
11
cm
−2
, the dislocation density
of CeO
2
shows a high sensitivity with that of YSZ compared with the low relativity
in lower dislocation density (< 2.4 × 10
11
cm
−2
). In addition, YSZ always has higher
dislocation densities and oriented curvatures than CeO
2
in each specimen, which can
be attributed to the smaller mosaic domain sizes in YSZ than in CeO
2
as observed by
high-resolution transmission electron microscopy.
PACS
68.55.Jk; 81.15.Fg
1 Introduction
Yttria-stabilized
ZrO
2
(
YSZ
)
and double
CeO
2
/YSZ
epitaxial growth
films on
Si
(001) substrates have at-
tracted much attention in recent years
due to their electric and optical appli-
cations such as insulators in silicon-on-
insulator (SOI) devices [1], optical coat-
ings [2] and buffer layers for supercon-
ductive [3] or ferroelectric [4] films on
silicon substrates. The use of a second
CeO
2
layer can induce a high-quality
upper layer [4] and reduce the lattice
mismatch and chemical reaction be-
tween
YSZ
and the upper layer, e.g. the
formation of a
BaZrO
3
layer between
YSZ
and
YBCO
[5]. Without a
YSZ
buffer layer, the direct growth of
CeO
2
on
Si
(001) usually has a
CeO
2
(111)
orientation rather than the
CeO
2
(001)
epitaxial one [6, 7]. However, in the
heteroepitaxial
CeO
2
(001)
/YSZ
(001)
/
✉ Fax: +81-3/5734-3369, E-mail: chun_hua_chen@hotmail.com
Si
(001) films, there are more than
5.0%
of lattice mismatches between the inter-
faces,
CeO
2
/YSZ
and
YSZ/Si
,where
the lattice constant of bulk
CeO
2
is
0.541 nm
,bulk
YSZ
is
0.514 nm
and
Si
is
0.543 nm
. This could lead to a multi-
plicity of defect structures including the
dislocations, lattice distortions, random
strains and mosaic domains, etc. [8].
These defect structures would strongly
affect not only the qualities of
YSZ
and
CeO
2
/YSZ
layers but also the structural
and electrical properties of the overall
devices [9–11]. Therefore, the qualita-
tive and quantitative analysis of defect
structure, that is the investigation of the
defect types and their concentrations in
YSZ
and
CeO
2
/YSZ
films, is import-
ant for the development of high-quality
devices.
The etch-pit densities (EPDs) and
transmission electron microscopy
(TEM) have been used to determine
threading dislocation densities in mis-
matched heteroepitaxial layers [12, 13].
A common disadvantage of these tech-
niques is their destructive nature. The
X-ray technique can provide non-de-
structive measurements of dislocation
densities with an accuracy equal to
EPD or TEM. Hordon and Averbach
described components of full width at
half-maximum (FWHM) of X-ray rock-
ing curves for the estimation of the
dislocation densities of metallic sin-
gle copper and aluminum crystals [14].
Based on their studies, Qadri and Di-
nan calculated the dislocation densities
of alloy heteroepitaxial
ZnCdTe/
InSb
films, which showed good agreement
with TEM observation [15]. Ayers ex-
tended the calculation technique to
a non-oxide
GaAs/
Si(001) single semi-
conductor layer by measuring several
rocking curves from different diffrac-
tion planes [16]. A simplified linear-
fitting technique has been developed in
their studies and is widely used for the
estimation of dislocation densities (de-
tails will be discussed in Sect. 3). How-
ever, it is important to notice that this
linear-fitting method is derived from
the single crystals and high-perfection
non-oxide semiconductor films, which
usually contain fewer defect types and
lower concentrations than the low-per-
fection oxide heteroepitaxial films, e.g.
YSZ/Si
or
CeO
2
/YSZ/Si
films. There-
fore, the conventional linear-fitting tech-
nique is not sufficient to evaluate the
defect type and the concentration in our
case. In this paper, we extend the afore-
mentioned theory with a modified tech-
nique to the case of double oxide hetero-
epitaxial
CeO
2
/YSZ/Si
(001) films with
various film thicknesses. By using a non-
linear full-parameter fitting method, de-
fect types and concentrations can be