1063-7397/05/3405- © 2005 MAIK “Nauka /Interperiodica”
0272
Russian Microelectronics, Vol. 34, No. 5, 2005, pp. 272–278. Translated from Mikroelektronika, Vol. 34, No. 5, 2005, pp. 327–333.
Original Russian Text Copyright © 2005 by Baru, Bayliss, Zhitov, Zakharov, Kartopu, Pokalyakin, Sapelkin, Stepanov, Timofeev, Shevchenko.
1. INTRODUCTION
Unlike microelectronics, optoelectronic devices are
very difficult to implement in conventional silicon,
because its band structure permits only indirect optical
transitions, making it a poor optical material. The last
decade has seen extensive research on low-dimensional
silicon structures, such as porous silicon and silicon
nanocrystals in a
SiO
2
matrix,
SiO
2
(Si). Photolumines-
cence (PL) and electroluminescence (EL) in the visible
region have been obtained from these materials at room
temperature. The mechanisms of the phenomena are
still controversial. In some cases, they are associated
with the size quantization of the electronic spectra in Si
nanocrystals; another important factor is the nanocrys-
tal–matrix interface.
The observation of intense PL and EL opens up pos-
sibilities for building an effective light source compati-
ble with integrated-circuit technology, which would
also represent a major advance in integrated optoelec-
tronics. Furthermore, silicon light-emitting diodes
could find application in optical interconnections for
very-large-scale-integration (VLSI) circuits.
The developments that have occurred in this field
relate mainly to SiO
2
(Si). This material is stable and
easy to fabricate; it constitutes an almost perfect active
medium for the excitation of PL. Optical amplification
under laser pumping in such films is among significant
advances that have recently been made toward the opti-
cally pumped Si laser [1, 2].
However, the present study is concerned with nano-
composite films containing Si nanocrystals embedded
in a
SiO
x
N
y
matrix,
SiO
x
N
y
(Si). The reason is that elec-
tric current rather than light is required for pumping in
light-emitting diodes and other devices. As compared
with
SiO
2
, the narrower energy gap of
SiO
x
N
y
is more
favorable for tunnel injection into the matrix and for
current pumping. Note also that the introduction of
nitrogen into
SiO
2
encourages the formation of Si
nanocrystals of small radius and high concentration,
makes for higher permittivity, etc. [3, 4].
Below we report on an experiment involving the
fabrication and characterization of
SiO
x
N
y
(Si) nano-
composite films. The focus is on (1) the structural study
by transmission electron microscopy (TEM) and
microdiffraction, (2) the measurement and examination
of PL spectra from films of different compositions and
structures, (3) the fabrication of metal–composite-
Structural and Luminescent Properties of SiO
x
N
y
(Si)
Nanocomposite Films
V. G. Baru*, S. Bayliss**, V. A. Zhitov*, L. Yu. Zakharov*, G. Kartopu**,
V. I. Pokalyakin*, A. Sapelkin**, G. V. Stepanov*
†
, A. A. Timofeev***, and O. F. Shevchenko*
*Institute of Radio Engineering and Electronics, Russian Academy of Sciences, Moscow, Russia
e-mail: Victor_Baru@mtu-net.ru
**De Montfort University, Leicester LE1 9BH, United Kingdom
***Moscow Institute of Engineering Physics (Technical University), Moscow, Russia
Received April 14, 2005
Abstract
—With a view to creating Si LEDs, the structural and luminescent properties of
SiO
x
N
y
films containing Si
nanocrystals in the
SiO
x
N
y
matrix are studied experimentally. It is found that the film structure (nanocrystal size
and concentration, the presence of an amorphous phase, etc.) and the spectrum and intensity of photolumines-
cence (PL) and electroluminescence (EL) are strongly dependent on the Si stoichiometric excess
δ
and anneal-
ing conditions. At
δ
ഠ
10%
, unannealed films are amorphous and contain Si clusters of size < 2 nm, as deduced
from the TEM and microdiffraction data obtained. Annealing at 800–1000
°ë
for 10–60 min produces Si crys-
tals 3–5 nm in size with a concentration of
ഠ
10
18
cm
–3
. The annealed films exhibit room-temperature PL and
EL over the wavelength range 400–850 nm with intensity peaks located at 50–60 and 60–70 nm, respectively.
The PL and EL spectra are found to be qualitatively similar. This suggests that both the PL and the EL should
be associated with the formation of luminescent centers at nanocrystal–matrix interfaces and in boundary
regions. However, the two phenomena should differ in the mechanism by which the centers are excited. With
the EL, excitation should occur by impact processes due to carrier heating in high electric fields. It is found that
as
δ
increases, so does the proportion of large amorphous Si clusters with a high density of dangling bonds. This
enhances nonradiative recombination and suppresses luminescence.
NANOSTRUCTURE
CHARACTERIZATION
†
Deceased.
@Phil_Robichaud
@deepthiw
@JoseServera