The effect of annealing on the photoluminescence of Si/SiOx
Qinyu Yang1,2, Dexin Wang1,2, Ying Guo1,2, Ke Ding1,2, Jing Zhang1,2
1， Department of Applied Physics，Donghua University, 2999 Renmin Rd., Songjiang
District, Shanghai 201620, P.R .China
2， Member of Magnetic Confinement Fusion Research Center, Ministry of Education,
Donghua University, 2999 Renmin Rd., Songjiang District, Shanghai 201620, P.R .China
Abstract: The photoluminescence（PL）of annealed porous SiO2 film embedded by Si
nanocrystals (Si-NCs) has been found emitting blue-light at room temperature
deposited by plasma-enhanced chemical vapor deposition(PECVD) at near-atmosphere
pressure. The SiO2 films obtained by PECVD had rare Si-NCs embedded in them. The
blue-light emission peak located at 418nm of porous SiO2 films was faint because
their surface was passivated by hydrogen. In order to improve the PL intensity, the
deposited films were annealed in primary gas at 5000C for 3 hours. Compared to
unannealed films, the PL peak of annealed films shift from 418nm to 397nm, and the
intensity strengthened obviously. The transmission electron microscopy（TEM）and
Fourier transform infrared spectroscopy (FTIR) revealed that Si-NCs emerged after
annealing while Si-H bonds decreased. Si-NCs were thought as the origin PL of 397nm.
The decrease of Si-H irradiative centers improved the PL intensity.
Key Words: Photoluminescence, Si nanocrystals(Si-NCs), annealing
deposition (PECVD) is often used to
1. Introduction
The
discovery
of
efficient
room-temperature photoluminescence (PL)
from Si nanostructures such as porous Si [1]
and Si ultrafine particles [2] has stimulated
a worldwide research. Si nanocrystals
(Si-NCs) embedded in SiOx (Si/SiOx) are
considered as one of the most promising
Si-based light-emitting materials because of
their appreciable and stable light emission,
as well as their robust structure. In recent
years, plasma-enhanced chemical vapor
prepare SiOx films. Compared with the
conventional
CVD
method,
the
deposition temperature of PECVD is
lower, and the optical and electrical
properties
of
the
films
are
accommodated easily by changing the
process parameters [3,4]. Si/SiOx is
usually prepared by thermal annealing of
amorphous silicon suboxides (a-SiOx, 0<x <
2) deposited by various methods [5–10],
since a-SiOx is thermodynamically unstable
and a chemical disproportionation reaction
electron
microscopy
takes place upon high temperature annealing,
deposited films were scraped from substrate
leading to the formation of Si /SiOx[6,11].
and
mixed
with
(TEM).
KBr
powder
The
and
emission
characterized by NEXUS － 670 Fourier
characteristics of as-prepared and annealed
transform infrared spectra (FTIR) for their
Si/SiOx were investigated. It was found that
chemical structure.
the blue emission intensity was dependent
3. Results and discussions
In
this
paper,
the
blue
Fig.1 depicted the PL spectra of the
on the Si-NCs after annealing. After coating
with annealing, the intensity increased.
as-prepared and the annealed Si/SiOx
2. Experiment
films. The PL spectrum of as-prepared
In the experiments, the plasma discharge
Si/SiOx film exhibited the broad peak
zone was formed and concentrated between
from 400nm to 470nm, whose center
two paralleled comb electrodes supplied
located at 418nm. After annealing at
with 20kHz, 7500V high voltage. The
5000C for 3 hours, the intensity of the
substrate was put 2 cm away from the
sample was stronger than that of the as-
plasma zone along the downstream direction
prepared one. Furthermore, the PL center
of the carrier gases. Silane（SiH4） was used
blue shifted to 397nm, which was reported
as the precursor gas and carried into the
in paper [12].
system by a mixture of argon and hydrogen
The FTIR spectrum of the as-prepared
(Ar:H2=95:5). The flow rate of SiH4 and the
and the annealed Si/SiOx films was shown
carrier gas was fixed at 20 sccm and at
in Fig.2. The peaks at around 1083 cm-1,
2L/min respectively through mass flow
820 cm-1 and 460 cm-1 were from
controllers. The operation pressure was kept
Si-O-Si stretching modes [13]. The
at 200 Torr. The deposition time was 5
oxygen
minutes for all the samples. Because of
survived water in pores of the porous SiOx
600
obverses porous. After deposition, the SiOx
500
0
film was annealed in primary gas at 500 C
for 3 hours.
PL experiment was performed by
HITACHI
F-4500
Spectrophotometer
with
Fluorescence
an
excitation
wavelength of 320 nm. The crystallinity of
deposited nanomaterials was characterized
with
Hitachi
H － 800
transmission
Intensity(a.u)
higher pressure, the deposited SiOx film
might
originate
397nm
from
the
418nm
400
300
Annealing time of 3 hours
200
100
As grown
0
300
400
500
600
Wave Length（nm）
Fig.1. PL spectra of as-prepared and
annealed Si/SiOx
films or the survived oxygen in reactant
from the oxygen bonds within the film
gas. The absorption peak at 621 cm-1
before annealing-induced regrowth [16].
originated from the Si-Si bonds vibration
Amorphous SiOx possessed huge number
on the surface and near surface region of
Si-H danging bonds, which can be also
-1
SiOx film [14]. 875cm was related to the
acted as irradiative centers. After annealing,
Si-H vibration because hydrogen was
the amorphous SiOx crystallized into
absorbed on the surface of the porous
crystalline silicon. Blue shift to 397nm of
SiOx[15]. It could be seen that the intensity
PL came from Si crystalline quantum dots.
of the Si-O-Si modes increased after
It was well known that the unstable Si-Hx
annealing, indicating that the porous SiOx
dangle bonds were progressively replaced
was more oxidized during annealing.
with more stable Si-O-Si bonds during
Moreover, the intensity of Si-H decreased
annealing, so in FTIR spectrum of as
after annealing, meaning that the hydrogen
prepared and annealing porous Si/SiOx, the
on the surface was desorbed during
peak
annealing.
disappeared after annealing. Meanwhile,
TEM
analysis
was
performed
to
confirm the formation of Si-NCs in the
related
to
Si-H mode
almost
Si-H bonds as irradiative centers on the
surface were passivated. That is why the
SiOx after annealing. Fig.3 (a) revealed that
no crystal was observed before annealing,
SiOx was amorphous. Such tiny Si-NCs
exhibited diameters of only 1.6-2.0nm after
annealing Si/SiOx.
Before annealing, 418nm PL originated
Fig.2. FTIR spectra of as-prepared and
annealed Si/SiOx
Fig.3. TEM images of (a) as-prepared and
(b) annealed Si/SiOx
PL intensity increased after annealing [17].
Yoshida, S. Onari (2001) J. Appl. Phys.
4. Conclusion
90 :5075-5080
[8] D. Riabinina, C. Durand, M. Chaker, F.
The blue emission from porous SiOx asprepared and annealed was reported. The
intensity of PL increased and blue shift at
the same time during annealing. Si-NCs
emerging after annealing were thought as
the origin PL at 397nm. The decrease of
Si-H irradiative centers improved the PL
intensity.
Rosei (2006) Appl. Phys. Lett. 88: 073105.
[9] F. Fang, W. Zhang, J. Sun, N. Xu, J. Zhu,
Z.F. Ying, J.D. Wu (2009) J.Mater. Res. 24:
2259.
[10] O.M. Feroughi, C. Sternemann, Ch.J.
Sahle, M.A. Schroer, H. Sternemann, H.
Conrad,A. Hohl, G.T. Seidler, J. Bradley, T.T.
Fister, M. Balasubramanian, A. Sakko,K.
Acknowledgement
Pirkkalainen, M. Tolan (2010) Appl. Phys. Lett.
The authors would like to acknowledge the
96:081912
supports
Science
[11] H. Takagi, U. Ogawa, Y. Yamazaki, A.
Foundation of China (Grant No 10775031,
Ishizaki, T. Nakagiri (1990) Appl. Phys.
10835004 and 11005017).
Lett. :56:2379.
of
National
Nature
[12]R.Kumar,Y.Kitoh,K.Hara
References
[1] L.T. Canham (1990) Appl. Phys. Lett. 57
1046-1048
(1993)
Appl.Phys.Lett.63: 3032-3034
[13]H.Li,D.Xu,G.Guo,L.Gui,Y.Tang,X.Ai,Z,Su
n,X.Zhang,G.G.Qin
(2000)
J.Appl.Phys.88:
4446-4448
[2] D.J. Lockwood (1998） Academic Press,
San Diego: Chapter 7
[3]H.-Y.Kim,J.-B.Shin.R.J.-Y.Lee (1999)
J.Vac.Sci.Technol.A 17:3240-3245
[4]Y.-K.Yang,J.-S.Shin,R.-G.Hsieh,J.-Y.gan,J.Y.Gan(1994)
Appl.Phys.Lett.64(12) :1567-1569
[5] W.M. Arnoldbik, N. Tomozeiu, E.D. van
Hattum, R.W. Lof, A.M. Vredenberg and
F.H.P.M. Habraken (2005) Phys. Rev. B:
71:125329.
[6] K. Furukawa, Y. Liu, H. Nakashima, D.
Gao, K. Uchino, K. Muraoka, H. Tsuzuki (1998)
Appl. Phys. Lett. 72: 725-727
[7] T. Makino, Y. Yamada, N. Suzuki, T.
[14]T.F.Young,C.P.Chen,J.F.fiou
(2000)
J.
Porous Silicon Mater 73:39-343
[15] Liu Peng, Wang Qirui, Li Xi, Zhang
Chaocan (2009)Colloids and Surfaces A:
Physicochem. Eng. Aspects 334:112-115
[16] Zhao X, Schoenfeld O, Kusano J, Aoyagi
Y, Sugano T(1994) Jpn J Appl Phys.33:L899
[17] Yue Zhao, Deren Yang, Dongsheng Li,
Minhua Jiang, (2005) Applied Surface Science
252:1065-1069