Influence of substrate temperature on the photoluminescence properties
of silicon carbide films prepared by ECR-PECVD
J. Huran1, M. Kučera1, A.P. Kobzev2, A. Valovič1, N.I. Balalykin2 and Š. Gaži1
1
Institute of Electrical Engineering, Slovak Academy of Sciences, Dúbravská cesta 9,
Bratislava, 841 04, Slovakia
2
Joint Institute for Nuclear Research, 141980 Dubna, Russian Federation
Abstract: Silicon carbide films were grown at various deposition temperatures
from 350 to 600 oC by means of electron cyclotron resonance (ECR) plasma
deposition with two gas mixtures. The concentration of elements in the SiC films
was determined by Rutherford backscattering spectrometry (RBS). The hydrogen
concentration was determined by the elastic recoil detection (ERD) method.
Chemical compositions were analyzed by infrared (IR) spectroscopy.
Photoluminescence (PL) spectra were measured at 293 K. The concentration of
hydrogen was decreased with increasing deposition temperature in the range
from 32 to 18 at.%. The films contain a small amount of oxygen. IR results
showed the presence of Si-C, Si-N, Si-H, C-H and Si-O bonds. The PL results
showed decreasing of the PL intensity with increasing a sample deposition
temperature. At the same time, from the spectra one can assess a gradual
broadening of the spectra and an increase of a relative portion of the low-energy
tail.
Keywords: silicon carbide, plasma deposition, photoluminescence
1. Introduction
Thin-film manufacturing methods using gas mixture
consisting of two or more gases such as SiH4 – CH4
is used for the production of thin-film transistors and
other electronic devices and industrial products [1].
Silicon carbide has attracted much interest for wide
range of applications. With its wide band gap,
excellent thermal properties and large bonding
energy, silicon carbide films are ideal for
optoelectronic blue and ultra-violet wavelength
emissions operating at high power levels, high
temperatures and caustic environments [2]. For
example, a-Si1-xCx:H was used as a wide window
material to enhance the conversion efficiency of
amorphous solar cell. The significance of this
material follows from the fact that its electrical and
optical properties can be controlled by varying the
carbon, silicon and hydrogen composition of the
film. PECVD technique offers an attractive
opportunity to fabricate amorphous hydrogenated Ndoped SiC films at intermediate substrate
temperatures and it provides high quality films with
good adhesion, good coverage of complicated
substrate shapes and high deposition rate [3].
Recently, Si-rich a-SiCx:H films have attracted new
attention in the photovoltaic community, since this
material has shown excellent electronic surface
passivation of c-Si comparable with thermal SiO2
and low temperature amorphous silicon nitride (aSiNx) passivation [4]. Silicon carbide films were
deposited on silicon substrate with ECR-CVD
reactor and photoluminesce was measured at
temperatures betwen 100 and 300 K [5]. It consist of
a relatively broad band centered around 450 nm and
a second narrow band at 400 nm in the near
stoichiometric samples. The crystalisation of SiC
correlates with the occurence of a strong PL band
which is strongly reduced after hydrogen passivation
[6]. Thus PL signal orriginates from the SiC matrix.
ECR plasmas are usually operated at low pressure 10
mTorr with the ECR resonant chamber placed at
some distance away from the substrate. Lowpressure operation results in the decomposition of
source gas molecules by collisions with high-energy
non-Maxwellian electrons, forming a high density
stream of charged species.
In this contribution the attention has been focused to
the structural and photoluminescence properties of
silicon carbide films prepared by the electron
cyclotron resonance plasma enhanced chemical
vapour deposition (ECR-PECVD). The structural
properties were investigated by RBS, ERD, IR and
PL measurement technique was used for
photoluminescence
properties
investigations.
Spectroscopic ellipsometry (SE) was used for
thickness and refractive index measurements.
determined by spectroscopic ellipsometry. For this
purpose a SpecEl-200 spectroscopic ellipsometer
(400 - 900 nm) manufactured by Micropac, software
Scout from Wolfgang Theiss and OJL model was
used. Photoluminescence spectra were recorded at
the room temperature. The samples were pumped by
20 mW power of a 488 nm line of an argon ion laser.
The luminescence radiation was filtered by a
quarter-meter monochromator and detected by a
photomultiplier tube. The detector signal was
amplified by a standard lock-in technique.
3. Results and discussion
Silicon carbide films were grown at various
deposition temperature from 350 to 600 oC by means
of ECR plasma deposition with two gas mixtures: 1.
gas mixture, SiH4(5 sccm), CH4(14 sccm), Ar(6
sccm), NH3(2 sccm), samples P1(substrate
temperature 350 oC), P2(450 oC), P3(550 oC) and 2.
gas mixture SiH4(5 sccm), CH4(14 sccm), H2(6
sccm), NH3(2 sccm), samples P4(350 oC), P5(450
o
C), P6(600 oC). A p-type silicon wafer with
resistivity 2-7 Ωcm and (100) orientation was used
as the substrate for the SiC films. The concentration
of species in the SiC films was determined by
Rutherford backscattering spectrometry (RBS). The
hydrogen concentration was determined by the
elastic recoil detection (ERD) method, figure 1.
He - beam
Target
Al - filter
RBS – detector, D2
ERD – detector, D1
Figure. 1. The experimental ERD method arrangement. The
sample orientation to the 4He+ beam was at an angle α = 15o.
The detectors were fixed in the following geometry: detector D1
at an angle Θ1 = 30o, detector D2 at an angle Θ2 =135o.
Chemical compositions were analyzed by infrared
spectroscopy. The IR spectra were measured from
4000 to 400 cm-1. Film morphology was assessed by
SEM. The thickness and refractive index were
RBS(Fig.2.) and ERD(Fig.3.) analysis indicated that
the films contain silicon, carbon, nitrogen, hydrogen
4000
RBS
simulated
3000
Counts
2. Experiment
interface
SiC/Si
2000
sample P5
C
N
1000
sample P2
0
300
400
500
600
700
800
Channel
Figure 2. RBS spectra of samples P2 and P4 which represent
spectra from all samples of both series.
and small amount of oxygen. The concentrations
were for 1. series(1.gas mixture) of samples :
Sample P1(silicon 28 at.%, carbon 34 at.%,
hydrogen 27 at.%, nitrogen 9 at.%, oxygen 2 at. %);
Sample P2(30, 35, 22, 10, 3); Sample P3(31, 37, 18,
11, 3); respectively. The concentrations were for 2.
series(2.gas mixture) of samples : Sample
P4(silicon27 at.%, carbon 34 at.%, hydrogen 32
at.%, nitrogen 7 at.%, oxygen 2 at.%); Sample
P5(29, 35, 26, 7, 3); Sample P6(31, 37, 19, 8, 5);
respectively. From the concentration results we can
conclude that the concentration of hydrogen was
decreased with increasing deposition temperature
and change a little with changing carrier gas argon to
hydrogen. Spectroscopic ellipsometry analysis
600
2.0
ERD
PL intensity (a. u.)
500
simulated
Counts
400
300
sample P5
200
sample P2
PL
T = 293 K
P1
1.5
1.0
P2
0.5
P3
100
0
200
0.0
1.4
300
400
500
600
1.6
700
1.8
2.0
Energy (eV)
2.2
2.4
Channel
indicated that the refractive index were in the range
of 2.2 to 2.3 for all samples and change a little with
the change of deposition temperature and gas
mixtures. The thickness of films was in the range of
150-160 nm and decrease a little with increasing
deposition temperature. It was not shown influence
of gas mixture on the deposition rate. The measured
IR spectrum revealed the main absorption region
between 400 and 2000 cm-1. IR results showed the
presence of Si-C, Si-O, Si-N, Si-H, N-H, C-H, C-N
specific bonds. The main phonon or vibration
frequency is related to SiC and have the
characteristics determined from the reflection
spectra: center position 795 cm-1 and non stressed
phonon position of cubic SiC is 796 cm-1. In
amorphous material a shift to higher values indicate
on recrystallisation or nucleation of small
crystallites. Figure 4 shows PL spectra for 1.series of
samples. In the figure, we can see a gradual decrease
of the PL intensity with increasing sample
deposition temperature. At the same time, from the
spectra one can assess a gradual broadening of the
spectra and an increase of a relative portion of the
low-energy tail. Such luminescent properties are
often the attributes of a worsened quality of material,
as could be the crystalline imperfection or a higher
concentration of non-radiative centers. From the
above introduced data is shown that with increasing
the deposition temperature, the hydrogen amount in
the samples falls down. It is known that hydrogen
passivates dangling bonds in such a type of a
material. Indeed, one can see coincidence of this
observation with a gradual degradation of PL
spectra. Figure 5 depicts PL spectra of the 2.nd
series of the samples. The shape of the spectra and
4
PL intenzity (a. u.)
Figure 3. ERD spectra of samples P2 and P4 which represent
spectra from all samples of both series.
Figure 4. PL spectra of samples P1, P2 and P3 measured at
room temperature with different deposition temperature.
P4
PL
T = 293 K
3
P5
2
1
P6
0
1.4
1.6
1.8
2.0
2.2
2.4
Energy (eV)
Figure 5. PL spectra of samples P4, P5 and P6 measured at
room temperature with different deposition temperature.
their overall tendency with the growth temperature
increase are the same as for the 1.st one (besides of
the small difference between the spectra of samples
P4 and P5). Therefore the conclusion made for series
1 is also here valid. For all PL spectra, the lowenergy tail is rapidly cut because of a large decrease
of the photomultiplier intensity at approx. 820 nm.
Figure 6 shows high resolution SEM image that
illustrates hemispherical surface morphology with
evident nanoscale grain size. This image represents
Acknowledgement
This research has been supported by the Slovak
Research and Development Agency under the
contracts APVV-0713-07, SK-UA-0011-09 and by
the Scientific Grant Agency of the Ministry of
Education of the Slovakia and Slovak Academy of
Sciences, No. 2/0192/10; 2/0153/10; 2/0144/10.
References
Figure 6. High resolution SEM image of top surface of silicon
carbide thin film (sample P5).
top surface of sample P5 prepared at 450 oC and is
practically identical for all samples but with small
increasing grain size with increasing deposition
temperature.
4. Conclusions
We have investigated the structural and
photoluminescence properties of SiC films prepared
by electron cyclotron resonance plasma enhanced
chemical vapor deposition at temperatures 350 oC to
600 oC. The RBS results showed that the
concentrations of Si, C and N in the films were
changed a little with the change of deposition
temperature. The concentration of hydrogen was
decreased with increasing deposition temperature in
the range from 32 to 18 at.%. The films contain a
small amount of oxygen. IR results showed the
presence of Si-C, Si-N, Si-H, C-H and Si-O bonds.
PL results showed the decreasing of the PL intensity
with increasing a sample deposition temperature. At
the same time, from the spectra one can assess a
gradual broadening of the spectra and an increase of
a relative portion of the low-energy tail. With
increasing the growth temperature, the hydrogen
amount in the samples falls down. It is known that
hydrogen passivates dangling bonds in such a type
of a material. Indeed, one can see coincidence of this
observation with a degradation of PL spectra.
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