APPLIED PHYSICS LETTERS
VOLUME 75, NUMBER 14
4 OCTOBER 1999
Evidence of energy coupling between Si nanocrystals and Er3؉
in ion-implanted silica thin films
C. E. Chryssou,a) A. J. Kenyon, T. S. Iwayama,b) and C. W. Pitt
Department of Electronic and Electrical Engineering, University College London, Torrington Place,
London WC1E 7JE, United Kingdom
D. E. Hole
School of Engineering, University of Sussex, Falmer, Brighton BN1 9QH, United Kingdom
͑
Received 24 May 1999; accepted for publication 4 August 1999͒
3
ϩ
Silica thin films containing Si nanocrystals and Er were prepared by ion implantation. Excess Si
concentrations ranged from 5% to 15%; Er3 concentration for all samples was 0.5%. Samples
exhibited photoluminescence at 742 nm ͑attributed to Si nanocrystals͒, 654 nm ͑defects due to Er3
implantation͒, and at 1.53 m ͑intra-4f transitions͒. Photoluminescence intensity at 1.53 m
increased ten times by incorporating Si nanocrystals. Strong, broad photoluminescence at 1.53 m
ϩ
ϩ
3
ϩ
was observed for Pump away from Er absorption peaks, implying energy transfer from Si
nanocrystals. Erbium fluorescence lifetime decreased from 4 ms to 1 ms when excess Si increased
from 5% to 15%, suggesting that at high Si content Er3 ions are primarily situated inside Si
nanocrystals. © 1999 American Institute of Physics. ͓S0003-6951͑99͒04040-1͔
ϩ
Recently, room-temperature light emission from porous
form nc-Si distribution ͑nanocrystal sizes ranged between 1
and 4 nm͒.
1
2
Si, Si-rich silica thin films, and Si nanocrystals ͑nc-Si͒ in
3
The annealed samples were implanted with Er3ϩ. Im-
plantation energies ranged between 80 and 380 keV and the
peak Er3 concentration was 0.5 at. % ͑ion doses ranged
silica matrices has been demonstrated. Nanometer-sized Si
particles exhibit unique electrical and optical properties not
ϩ
3
ϩ
observed in bulk material. Er -doped Si has also attracted
interest for its applications in silicon optoelectronics. Er3 is
attractive because its 1.53 m emission coincides with the
between 7.5ϫ1014 and 2.4ϫ10 ions/cm ͒. The calculated
15
2
ϩ
depth profile of Er3 is shown in Fig. 1. It is apparent that
ϩ
3
ϩ
3
ϩ
most of the incorporated Er sees a nanocrystal environ-
low attenuation region of silica optical fibers and Er -doped
ment. Er3 implanted samples were not annealed in the
ϩ
4
,5
Si has received much attention. Energy coupling between
3
ϩ
3
ϩ
present experiment. Prior to Er implantation the samples
exhibited luminescence only at about 1.7 eV due to nc-Si, as
published in Ref. 9. Photoluminescence ͑PL͒ intensities and
peak energies were strongly affected by the excess Si con-
Si nanoclusters and Er
was first demonstrated in
3
ϩ
Er -doped Si-rich silica thin films produced by plasma-
6
enhanced chemical vapor deposition and was recently dem-
3
ϩ
7
onstrated in cosputtered Er -doped silica thin films; a simi-
lar effect is also seen in chalcogenide glasses.8 This is
potentially important since it may relax requirements on the
centration; the 1.7 eV peak shifted to lower energies with
increasing concentrations of excess Si atoms.9
Room-temperature PL from samples was studied using
3
ϩ
Er pump source and lead to broadband pumped optical
devices.
ϩ
an Ar laser, a single grating monochromator, and standard
lock-in techniques. An InGaAs photodiode and a photomul-
tiplier tube were used to detect infrared and visible spectra,
respectively. Spectral response of the detection system was
calibrated using a tungsten white light source. For fluores-
In this study we demonstrate energy coupling between
3
ϩ
nc-Si and Er ions in ion-implanted silica thin films. Ion
implantation is a promising technique for producing Si
9
3ϩ
10
nanocrystals and also incorporating Er into thin films.
ϩ
Samples were prepared by implanting Si into thermally
oxidized Si ͑oxide thickness around 300 nm͒. Six implanta-
tion energies were used between 25 and 200 keV: peak ex-
cess Si concentrations were between 5 and 15 at. % ͑ion
doses ranged from 1.0ϫ1016 to 2.0ϫ10 ions/cm ͒. Depth
17
2
1
1
profiles of implanted Si ions were calculated using TRIM as
a first approximation, and are shown in Fig. 1. Samples were
subsequently annealed at 1050 °C in a flowing N atmo-
2
9
sphere for 8 h to form Si nanocrystals. Transmission elec-
tron microscopy analysis of annealed samples showed uni-
a͒Author to whom correspondence should be addressed. Electronic mail:
b͒
Permanent address: Department of Materials Science, Aichi University of
FIG. 1. Predicted plot of concentration profiles, calculated using TRIM, for
ion-implanted Si and Er in silica using a range of implantation energies.
Education, Igaya-cho, Kariya-shi, Aichi 448-8542, Japan.
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:
003-6951/99/75(14)/2011/3/$15.00 2011 © 1999 American Institute of Physics
30.216.129.208 On: Fri, 05 Dec 2014 02:07:10
0
1