1. Thin Solid Films 326 (1998) 92–98
The preparation of photoluminescent Si nanocrystal–SiOX films
by reactive evaporation
S. Zhang*, W. Zhang, J. Yuan
State Key Laboratory of Si Material Science, Zhejiang University, Hangzhuo, PR China 310027
Accepted 13 February 1998
Abstract
Si nanocrystals–SiOx films on Si substrates have been prepared by evaporating Si or SiO in the residual gas of the system or in an oxygen
atmosphere by introducing oxygen into the deposition chamber. Films with different oxygen concentration and different Si crystallite size
were obtained by changing the substrate temperature and the oxygen partial pressure. It is observed that only the films prepared by
evaporating SiO in an oxygen atmosphere are photoluminescent at room temperature. The possible mechanism for the luminescence is
discussed, according to the results of X-ray photoelectronic spectroscopy (XPS), infrared (IR) spectra and X-ray diffraction (XRD)
measurements. © 1998 Elsevier Science S.A. All rights reserved
Keywords: Evaporation; Luminescence; Nanostructures; Silicon oxide
1. Introduction luminescence layer and metal contacts used as electrical
leads may be finished in the same system without breaking
Since the observation of photoluminescence from Si/SiO2 vacuum; (3) because reactive evaporation is an alternative
multilayers [1], Si nanocrystals in SiOX matrix are exten- technique in preparing SiO2, which is extensively used as
sively studied due to their unique optical properties and the the masks in the Si devices and integrated circuit fabrication
simplicity of producing them, as well as the technological and as the insulating layer in metal-oxide-semiconductor
compatibility with present Si integrated circuits. They may devices, it is possible to make masks or insulating layers
provide a simple way to realize stable Si-based luminescent or luminescent films by the same technique, i.e. it is more
devices, making integrated optoelectronic devices possible compatible to the semiconductor device processing. It is the
on Si chips. Several techniques have been employed to purpose of this paper to use a simple and convenient proces-
make the structure of Si nanoparticles in SiO2, which sing technique to realize rather difficult results, though the
include single energy Si ion implantation into SiO2 [2–4], results presented are initial and the processing conditions
low temperature multienergy Si+ ion implantation into SiO2 have not been optimized yet. In term of scientific interests,
[5], plasma enhanced chemical vapor deposition [6], two films with a wide range of compositions and crystalline
step thermal annealing with auxiliary use of high pressure structures can be obtained, which might be difficult to rea-
[7] and sputtering [8]. However, there is no report on the lize by other techniques. This should be helpful in under-
preparation and luminescence from Si nanocrystals – SiOx standing the mechanism of luminescence from Si–SiO2
films deposited by simple evaporation (including reactive films.
evaporation), which are studied in the present experiment.
Compared to other techniques, reactive evaporation has
the following advantages: (1) the technology is simpler and 2. Experimental
the system to prepare them is more available, because eva-
poration is one of the techniques most often used in semi- Two-inch (111) oriented Si wafers were used as the sub-
conductor processing and other film depositions; (2) the strates. They were cleaned using RCA1 solution (NH4OH:-
H2O2:H2O = 1:1:5), followed by RCA2 solution (HCl:
* Corresponding author. Fax: +86 571 7951360. H2O2:H20 = 1:1:5), each for 15 min at 358 K. Then they
0040-6090/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved
PII S0040-6090 (98 )0 0532-X

2. S. Zhang et al. / Thin Solid Films 326 (1998) 92–98 93
were dipped into 10% hydrofluoric acid (HF) solution for 10 persed by a double-grating 0.64 m monochrometer (HRD1)
s to remove native SiO2 on the Si surface. The substrate was and the slits were set at a width of 300 mm. A GaAs photo-
immediately transferred into the chamber from the solution multiplier in the photon counting mode was used as the light
and the chamber was pumped down. The substrate was detector. Data were recorded at intervals of 1 nm in 0.5 s.
heated from the backside by thermal radiation of coiled The sample was kept in air and remained at room tempera-
tungsten in closely arranged parallel quartz tubes. For uni- ture.
form substrate temperature, the radiator was 2 cm away Infrared (IR) spectra were measured at room temperature
from the substrate and the area of the radiator was three in a single beam mode. The absorption by Si substrate was
times larger than that of the substrate. Three groups of sam- removed by subtracting the spectrum of the bare substrate
ples were prepared. Groups 1 and 2 were made by evapor- from the spectra of samples.
ating ultra-pure Si (99.999%), respectively in the residual We have observed the film surfaces using scanning elec-
gas of the deposition chamber with a base pressure of tron microscopy. Smooth surfaces were often obtained,
5 × 10−3 Pa and in an oxygen atmosphere by introducing except for the films which contained large size of Si crystal-
pure oxygen (99.99%) into the chamber. Group 3 was lites. Some voids were observed in those samples. High
made by evaporating pure SiO (99.99%) in the oxygen resolution transmit electronic microscopy (HRTEM) was
atmosphere. Both Si and SiO were evaporated using an e- not performed for the samples.
gun. The beam current of the gun in preparing groups 1 and
2 was maintained at 0.3 A. In evaporating SiO, the beam
current was reduced to 0.1 A. The deposition started by 3. Results
opening the shutter after the substrate temperature, the Si
evaporation rate and the reactive gas pressure were stable. 3.1. Films in group 1
The film thickness determined with a deflected stylus varied
from 1 to 13 mm for different samples, due to various eva- Fig. 1 shows XRD spectra for three samples prepared
porating materials and different deposition time, as well as without intentionally introducing oxygen into the system
the effect of substrate temperature (Ts) and the partial pres- at substrate temperatures (Ts) of 673, 1013 and 1113 K,
sure of reactive gases on the deposition rate. The effect of respectively. Fig. 1a shows one peak only at 2v = 28.34°.
thickness on the film properties have not been studied yet. The peak position and FWHM are the same as the substrate
No other elements were found in the resulting films by X- without any film deposited (bare substrate). However, the
ray photoelectronic spectroscopy (XPS) except for Si, O and intensity of the peak from this sample is about 1/8 of the
C which is unavoidable in XPS measurement. bare substrate because the film reduces the diffraction inten-
X-Ray diffraction (XRD) was used to determine film sity. The result implies that the peak is due to the diffraction
structures. Ka lines from Cu were used as the X-ray source. from the substrate, and the deposited film is amorphous
Data were taken at intervals of 0.02 s. The instrument was which is not thick enough to show its amorphous structure
set so that Si (111) peaks resulting from the diffraction of in the XRD spectrum.
Ka1 and Ka2 lines could be distinguished obviously. For the sample prepared at Ts = 1013 K, six peaks occur
XPS, performed in ESCALAB MKII, was used to deter- as shown in Fig. 1b. They are at 2v = 28.34, 47.12, 55.8, 69,
mine the film composition and possible bounding configura- 76 and 88° and are related to the diffraction from Si (111),
tions. A monochromatic X-ray source from Al Ka1,2 (220), (311), (400), (331) and (422) planes, respectively.
guaranteed an instrument resolution of 0.8 eV full width Except for the Si (111) peak, the other five peaks are
at half maximum (FWHM). The angle between the sample obviously from the deposited film. Considering the facts
and the analyzer input was arranged so that an electron that the bottom of Si (111) peak is much broader than that
escape depth was about 2–5 nm, depending on the sample. in Fig. 1a or than that from the bare substrate, and that the
It was observed that serious oxidation occurred on the sur- intensity part (or narrow part) disappear in a 12 mm thick
faces of the samples with low oxygen concentration in sample, it is believed that the broad part is diffracted from
groups 1 and 2 after the samples were exposed to air. the film, while the intensity part is still from the substrate.
Hence, a 12 nm thick surface layer was removed by Ar The relative intensities for the last five peaks in this curve
ion sputtering in the preparation chamber of ESCALAB are close to those in powder Si. Hence, it is concluded that
MKII before the measurement was carried out. This may the film contains Si crystallites which grow at arbitrary
introduce error in determining the composition due to pre- orientation, instead of epitaxially. The reason why Si does
ferential sputtering effect. However, it should not signifi- not grow epitaxially will be discussed later. From FWHM of
cantly affect the following qualitative analysis on the the peaks in Fig. 1b, we can estimate the diameter d of the
composition. crystallite using the formula [9]:
Photoluminescent measurements were carried out at
09l
d=
:
room temperature and in air. Samples were excited by a B cosv (1)
413.10 nm line from krypton ion laser with an incident
power density of about 120 W/cm2. The spectrum was dis- where l is the wavelength of the X-ray used, B is the value

3. 94 S. Zhang et al. / Thin Solid Films 326 (1998) 92–98
of FWHM and v the Bragg diffraction angle of the peak.
The Si crystallite size for this sample is about 6.5 nm on
average, estimated from (220), (311) and (331) three dif-
fraction peaks. The accuracy of FWHM is about 15%. The
experiment shows that films containing smaller crystallites
can be prepared by reducing Ts. When Ts was 813°K, the
crystallite in the resulting films was about 5 nm calculated
from pretty weak (220) and (311) diffraction peaks (the
XRD curve is not shown).
Compared to Fig. 1b,c shows one more peak at
2v = 58.76°, which is associated with the second order dif-
fraction from (111) planes of the Si substrate. FWHMs for
all other peaks in Fig. 1c are narrower than those of corre-
sponding peaks in Fig. 1b, i.e. the crystallite in this sample
is larger than that of the sample prepared at Ts = 1013°K. If
Eq. (1) is still used, then the diameter of the crystallite
should be Ͼ12 nm.
These results show that the crystallite size significantly
depends on Ts, i.e. increasing with increasing Ts.
Fig. 2a is an XPS spectrum for the sample prepared at
1013 K and measured at a depth of 12 nm. Fig. 2b is the
enlarged XPS spectrum of the Si2P peak in Fig. 2a. No large
differences were observed in the depth profile of the oxygen
concentration, except on the surface. The Si2P peak can be
deconvoluted into two components as shown by Fig. 2b,
which are respectively located at the binding energy of
99.99 and 102.5 eV. The peak at 99.99 eV is attributed to
element Si and the peak at 102.5 eV to the Si which has
bound to the oxygen. Due to the surface charge effect, both
Fig. 2. (a) The XPS spectrum for the sample represented by Fig. 1b. (b)
Enlarged Si2p peak in (a) and its two deconvoluted components.
C1s and Si2P peaks in this sample shift about 0.7 eV. The
difference of the binding energies between element Si and
bound Si with O is about 2.5 eV, which is 1.7 eV smaller
than that between element Si and Si in SiO2. This can be
explained by the low oxygen concentration in the film. From
the area of Si2p and O1s peak the ratio of Si to O is calculated
and equal to 11:2 for his sample. From the deconvoluted two
Si2P peaks, it is roughly estimated that 27% of the total Si is
in the form of SiOx. The above calculation suggests that
x ≈ 0.7 in SiOx, even in the regions where Si and O have
combined, i.e. the oxygen concentration in the film is very
low.
The dependence of the oxygen concentration on Ts for the
measured samples is illustrated in Fig. 3. From the figure it
can be seen that the oxygen concentration increases with
increased substrate temperature. The oxygen concentration
is about 28% for the sample prepared at the substrate tem-
perature of 1113 K, compared to 11% prepared at 553 K.
3.2. Films in group 2
Fig. 1. XRD spectra for three typical samples in group 1, made at Ts = 673 To introduce more oxygen into the film, oxygen was
K (a), 1013 K (b) and 1113 K (c), respectively. filled into the deposited chamber in evaporating Si. Fig. 4

4. S. Zhang et al. / Thin Solid Films 326 (1998) 92–98 95
Fig. 5. XRD spectra for two samples in group 3. The sample for (a) was
made at an oxygen flow rate of 100 sccm and Ts = 513 K, while the sample
Fig. 3. The dependence of oxygen concentration on Ts in the resulting films for (b) was prepared at an oxygen flow rate of 150 sccm and Ts = 673 K.
of group 1.
the diameter of the crystallite is estimated to be less than 5
shows an XRD spectra for three samples prepared at a sub- nm. In Fig. 4a, (220) and (331) peaks overlap and turn into a
strate temperature of 1113 K and oxygen flow rate of 150 broad one, which together with the broad bottom of (111)
sccm (Fig. 4c), and at a substrate temperature of 1013 K, peak suggests that the film contains very small crystallites
oxygen flow rate of 100 sccm (Fig. 4b) and 150 sccm (Fig. with diameter Ͻ3 nm, estimated after the broad peak is
4a), respectively. As discussed above, the peaks at 28.34° in deconvoluted. From Fig. 4b,c we observed again that
Fig. 4 (also in Fig. 5) are the contributions of deposited films FWHM is reduced, or the crystallite size is increased with
as well as the substrate, while the peak at 58.7° is due to the increasing Ts for the same oxygen partial pressure or oxygen
second order diffraction from (111) planes of the Si sub- flow rate. The oxygen concentration for the sample repre-
strate. All other peaks diffracted from the films will be used sented by Fig. 4c is about 56%, the highest value in group 2.
to determine the crystallite size in the following. If Figs. 1c
and 4c are compared, it is noted that the corresponding 3.3. Films in group 3
peaks in Fig. 4c are broader. In Fig. 4b, (220) and (331)
peaks can be clearly distinguished and from these two peaks Fig. 5 shows XRD spectra for two typical samples in this
group. The sample for Fig. 5a was made at an oxygen flow
rate of 100 sccm and Ts = 513 K, while the sample for
Fig. 4. XRD spectra for three typical samples in group 2. They were
prepared at Ts = 1113 K and oxygen flow rate of 150 sccm (c), and at Ts
of 1013 K, oxygen flow rate of 100 sccm (b) and 150 sccm (a), respec- Fig. 6. IR absorption spectra. (a–c) relate to the samples represented by the
tively. curves in Fig. 4, while (d,e) relate to the samples in Fig. 5.

5. 96 S. Zhang et al. / Thin Solid Films 326 (1998) 92–98
Fig. 1b was prepared at an oxygen flow rate of 150 sccm and high frequency with increased x. When x = 2, the peak
Ts = 673 K. The measurement was done after the samples occurs at 1070 cm − 1. The peak at 1200 cm − 1 in Fig. 6b is
were annealed at 1073 K for 1 h in a 99.99% nitrogen atmo- from the crystobalite. The absorption peak of the crystoba-
sphere. Both curves show a broad diffraction peak near 22°, lite in single crystal Si locates near 1220 cm − 1 [11]. The
which is absent in Figs. 1 and 4 and is assigned to the reason why the peak occurs at a smaller wavenumber here
diffraction from (101) plane of crystobalite. The assignment may be due to the non-single crystalline structure of SiO2, as
for the peak is consistent with the result of infrared (IR) indicated by the XRD peaks in Fig. 5. Peaks near 486 and
absorption measurement given in Fig. 6. In addition, Fig. 800 cm − 1 are other vibration modes for SiOx (see Ref. [14]).
5a shows a broad peak between 40 and 60°, similar to Fig.
4a. Hence, the crystallite should be smaller than 3 nm. The 3.4. Photoluminescence
Si (111) peak in Fig. 4b is obviously diffracted from the
film, because this film is thick, which absorbs most of the X- Fig. 7 shows room temperature photoluminescence (PL)
rays incident or reflected from the substrate. No other Si spectra for typical samples in three groups. The two bottom
diffraction peaks can be observed in curve b, from which curves (Fig. 7a,b) are related to the sample represented
and the broad (111) peak it is suggested that the film has respectively by Figs. 1b and 4c. Fig. 7c,d are related to
amorphous structure, or at least the size of the crystallites (if the samples respectively represented by curves in Fig. 5.
any) in the film should be smaller than that in the sample All measurements were carried out after the samples were
represented by Fig. 4a. annealed as indicated above. Except that the oxygen con-
XPS measurement shows that the films in this group can centration in the annealed films was slight changed, no
have more stoichiometric SiO2 structure. The highest oxy- nitrogen was detected either by XPS or by IR. This is rea-
gen concentration can be up to 63% (the sample for Fig. 5b), sonable when considering the inactivity of N2. So far, no PL
which is much larger than the corresponding value in group at room temperature has been observed in the films of
1 (28%) and in group 2 (56%). groups 1 and 2. In group 3, samples with Si crystallite
The differences between three groups are also compared size Ͻ3 nm show a PL peak near 725 nm like Fig. 7c,
using IR measurements. Fig. 6 shows IR absorbance spectra while other samples with Si crystallite size ≥4 nm or
for five samples. Fig. 6a–c is related to the samples in group amorphous structure do not show obvious PL peaks, like
2, represented by the curves in Fig. 4, while Fig. 6d,e is Fig. 7d.
related to the samples in group 3 in Fig. 5. All data were
taken after an annealing in pure nitrogen for 1 h at a tem-
perature of 1073 K, or at 1173 K for the sample prepared at 4. Discussion
Ts Ͼ 1073 K. The curves show absorption bands centered
between 970 and 1060 cm − 1. In addition, both samples in The results presented above shows that the substrate tem-
group 3 (Fig. 6d,e) have a peak or apparent shoulder at 1200 perature and the gas in the deposition system are very
cm − 1 as indicated by a dashed line in the figure, which was important factors in controlling film structures and proper-
absent or very weak if any in groups 2 and 1 (the IR spectra ties. The oxygen and water vapor in the deposition chamber
for group 1 are similar to group 2 and are not shown in the play the role of oxidizing the Si substrate and the evaporated
figure). The peaks between 970 and 1070 cm − 1 are the Si on the substrate, which respectively prevent an epitaxial
stretching mode for SiOx [10], where the peak shifts to growth along the (111) orientation of the Si substrate, and
prevent Si crystallites growing large, and finally leads to Si
with non-single crystal structure. Ten percent oxygen on the
Si surface was detected when the substrate temperature was
set at 1113 K for 30 min in the residual gas with the base
pressure of 5 × 10−3 Pa, and then was transferred into the
XPS chamber immediately for the measurement [12]. The
oxidation effect on the crystallite size can be observed by
comparing FWHMs of the corresponding peaks of Fig. 1b
and Fig. 4a,b, as well as between two curves in Figs. 1c and
4. A larger oxygen flow rate gives a higher oxygen partial
pressure in the system and leads to more oxygen reacting
with Si. Then smaller crystallites are produced.
The substrate temperature can affect the mobility of eva-
porating atoms on the substrate, as well as the reaction rate
between Si and reactive gases. When the substrate tempera-
Fig. 7. Photoluminescence spectra measured with 413.10 nm laser excita-
tion at room temperature for four samples. The bottom two curves are
ture is increased for a fixed reactive gas pressure, the mobi-
respectively related to the samples in groups 1 and 2, while the top two lity of evaporated atoms on the growing surface is
curves to group 3. enhanced, while the oxidation rate, then the oxygen concen-

6. S. Zhang et al. / Thin Solid Films 326 (1998) 92–98 97
tration in the resulting films (as observed in group 1) will tallite size by XRD is not known, because it has not been
also be increased. The first effect favors the growth of large verified using another independent technique such as
size crystallite. On the other hand, the second effect will HRTEM. Hence, further measurements and investigation
prevent the increase in the Si crystallite size. The result are needed to tell the discrepancy and verify the lumines-
that the crystallite size is increased with increased Ts sug- cence mechanism suggested here.
gests that the mobility of Si on the substrate surface play
more important role in determining the crystallite size than
the oxidation effect. 5. Conclusions
In evaporating SiO, SiO is sublimated before it is decom-
posed, because the evaporation temperature is much lower Si–SiOx films on Si substrates have been prepared by
than its melting point. The evaporated SiO is reactive and reactive evaporation of Si or SiO. The reactive gases are
easy to form SiO2 through binding one more oxygen atom. provided by either the residual gas or oxygen intentionally
For the same Ts and oxygen partial pressure in the system, introduced into the system. It is observed that the oxygen
the probability to form SiO2 is higher by evaporating SiO concentration and the Si crystallite size in the resulting films
than by evaporating Si. However, it is still possible that can be controlled by changing the substrate temperature and
small number of SiO molecules are decomposed into Si the oxygen partial pressure, and both can affect the photo-
and O in the evaporation, and the Si atoms are coalesced luminescence significantly. Higher Ts gives larger Si crys-
to form crystallite in the deposition or in the annealing (as tallite for other fixed deposition conditions. On the other
observed). hand, higher oxygen partial pressure leads to smaller Si
Though we cannot definitely tell the mechanism for the crystallite and higher oxygen concentration in the film. No
observed PL, some literature has ascribed PL at long wave- luminescence has been detected at room temperature for the
length (Ͼ700 nm) to the quantum size effect [4,6,13,14]. On samples prepared by evaporating Si either in the residual gas
the one hand, in the experiment we have observed that the or in the oxygen atmosphere. A quite narrow luminescence
films with large Si crystallites or amorphous structure in any peak near 725 nm at room temperature is observed from the
group are not photoluminescent at room temperature, which samples with the Si crystallite diameter Ͻ3 nm but not
suggests that the crystallite size is important for PL. How- amorphous Si, prepared by evaporating SiO in the oxygen
ever, it is noted that the Si structure of the films in group 2 atmosphere. More data are required to extract a conclusion
can be the same as that for the sample represented by the top for the PL mechanism, though its possibility has been dis-
curve in Fig. 7, but PL efficiency is different, which sug- cussed in Section 4.
gests that other factors control the radiative transition effi-
ciency. The samples prepared using Si as the evaporating
material have low oxygen concentrations, no or very small Acknowledgements
SiO2 diffraction peaks in XRD (Figs. 1 and 4) and no 1200
cm − 1 peaks (or very small if any) in IR absorption (Fig. 6). It This work was supported by the Natural Science Founda-
is well known that a stoichiometric SiO2 can give a higher tion of Zhejiang Province, China and the Doctoral Founda-
energy barrier for the Si nanocrystal than SiOx with x Ͻ 2. tion of the Chinese Education Committee. The
According to the theory of the quantum size effect, the photoluminescence was measured in the Institute of Semi-
higher the energy barrier, the more the energy gap increases conductors, Chinese Academy of Sciences.
and the more efficiently the excess carriers transit radia-
tively in the Si nanoparticle quantum well for the same
size nanoparticles. This may explain why PL at room tem- References
perature can be observed in the samples of group 3, while
not in groups 1 and 2. The result and discussion may favour
[1] Z.H. Lu, D.L. Lockwood, J.M. Baribeau, Nature 378 (1995) 258.
the mechanism that the photoluminescence is from the [2] H.M. Cheong, W. Paul, S.P. Withrow, J.G. Zhu, J.D. Budai, C.W.
quantum size effect. It is interesting to note that Shi et al. White, D.M. Hembree Jr., Appl. Phys. Lett. 68 (1996) 87.
[14] recently reported a similar PL peak from Si rich SiO2 [3] S. Guha, M.D. Pace, D.N. Dunn, I.L. Singer, Appl. Phys. Lett. 70
films prepared by LPCVD and ascribed it to the quantum (1997) 1207.
[4] A. Pifferi, P. Taroni, A. Torricelli, G. Valentini, P. Mutti, G. Ghislott,
size effect also. We also find that our observation without
L. Zanghieri, Appl. Phys. Lett. 70 (1997) 348.
PL from amorphous Si–SiOX films is contradictory to the [5] W. Skorupa, R.A. Yankov, I.E. Tyschenko, H. Frob, T. Bohme, K.
report by Lu et al. [1]. They did observe PL from amorphous Leo, Appl. Phys. Lett. 68 (1996) 2410.
Si/SiO2 multilayers. In the moment, we do not believe that [6] A.J. Kenyon, P.F. Trwoga, C.W. Pitt, G. Rehm, J. Appl. Phys. 79
we can give a clear explanation for the discrepancy, because (1996) 9291.
[7] D.P. Karwasz, A. Misiuk, M. Ceschini, L. Pavesi, Appl. Phys. Lett.
we are not aware whether the properties of amorphous Si,
69 (1996) 2900.
such as defects in different geometric structures (dot and [8] V.G. Baru, A.P. Chermushich, V.A. Luzanov, G.V. Stepanov, L.Y.
layer) and prepared by different techniques are compatible Zakharov, K.P. O’Donnell, I.V. Bradley, N.N. Melnik, Appl. Phys.
or not. In addition, the accuracy in determining the Si crys- Lett. 69 (1996) 4148.

7. 98 S. Zhang et al. / Thin Solid Films 326 (1998) 92–98
[9] D. Cullity (ed.), Elements of X-Ray Diffraction, Addison–Wesley, [12] W. Zhang, S. Zhang, J. Yuan, Chinese J. Semicon. 18 (1997) 8.
London, 1956, p. 262. [13] A.A. Seraphin, S.T. Ngiam, K.D. Kolenbrader, J. Appl. Phys. 80
[10] J.C. Knights, R.A. Street, G. Lucovsky, J. Non-Cryst. Solids 35/36 (1996) 6249.
(1980) 279. [14] W.Q. Shi, Y.Z. Liu, Z.J. Chen, S.X. Liu, D.C. Yao, The Proceedings
[11] C.J. Varker, J.D. Whitefield, P.L. Fejes, in D.C. Gupta (ed.), Silicon of the 10th National Conference on Semiconductor, Chinese Institute
Processing, American Standards Test Manual, Philadelphia, PA, of Electronics, Qindao, 1997, p. 73.
1983, p. 369.