We measured at room temperature the photoluminescence spectra of the thermally oxidized Si1-x-yGexCy thin films which were grown on silicon substrates by plasma-enhanced chemical vapor deposition and the wet oxidized at 1100 °C for 20 min. The photoluminescence band with a peak at ~393 nm under the exciting radiation of λ = 241 nm was observed. Possible mechanism of this photoluminescence is discussed

Cheng, Xuemei

Han, Ping

Jiang, Ruolian

Liu, Xiabing

Lo, Zhiyun

Zang, Lan

Zheng, Youdou

Zhu, Shunming

English

Crossref

Scholarship, Research, and Creative Work at Bryn Mawr College | Bryn Mawr College Research

APPLIED PHYSICS LETTERS VOLUME 75, NUMBER 21 22 NOVEMBER 1999Room-temperature blue luminescence of thermally oxidized Si12x2yGexCythin films on Si 100 substratesXuemei Cheng, Youdou Zheng,a) Xiabing Liu, Lan Zang, Zhiyun Lo, Shunming Zhu, PingHan, and Ruolian JiangPhysics Department, Nanjing University, China, 210093~Received 24 May 1999; accepted for publication 28 September 1999!We measured at room temperature the photoluminescence spectra of the thermally oxidizedSi12x2yGexCy thin films which were grown on silicon substrates by plasma-enhanced chemicalvapor deposition and then wet oxidized at 1100 °C for 20 min. The photoluminescence band with apeak at ;393 nm under the exciting radiation of l5241 nm was observed. Possible mechanism ofthis photoluminescence is discussed. © 1999 American Institute of Physics.@S0003-6951~99!01147-X#During the last few years, special interest has been de-voted to the blue-green luminescence of silicon-based mate-rials because they have potential for becoming novel andfuture photoelectric devices. Among them, silicon-based ma-terials with nanostructures, such as porous silicon,1 oxidizedsilicon, and germanium nanocrystallites,2–5 oxidized SiCnanocrystallites,6 and so on, are perhaps under the most wideand complete investigations. However, another importanttype of silicon-based material luminescence, luminescencerelated to oxygen-deficient defects in amorphous SiO2films7–9 and Si(12x)Ge(x)O2 films,10,11 has been paid moreand more attention recently. Starting from Mitchell andPage’s work,9 many other groups have worked in this field.Skuja8 proposed that the well-known optical absorption bandat 5.03 eV and the luminescence band at 4.3 eV in amor-phous SiO2 are due to singlet-to-singlet transitions, while theluminescence band at 2.65 eV due to triplet-to-singlet tran-sitions in a silicon-related intrinsic defect, twofold coordi-nated silicon Si20. A characteristic photoluminescence ~PL!band at 3.1 eV in oxygen deficient SiO2:GeO2 was alsoobserved.10,12 In 1995 Ginzburg et al. proposed a physicsmodel based on the energy level arrangement of Si20~Ge20! toexplain some features of the blue luminescence in amor-phous Si(12x)Ge(x)O2.11 In addition, even for the cases ofthe luminescence in the nanostructure materials, the oxygendeficient luminescent centers are often taken intoconsideration.13Recently, the studies on Si12x2yGexCy alloys have beenpaid great attention because of the considerably greater flex-ibility, compared to that available in the Si12xGex /Si mate-rial system, to control strain and electronic properties ingroup IV heterostructure materials. Substantial improve-ments in the growth and characterizing of Si12x2yGexCy al-loys have already been achieved.14In this letter, we report the photoluminescence spectrafrom the thermally oxidized Si12x2yGexCy thin films on Si~100! showing a photoluminescence band with a peak at;393 nm under the exciting radiation of l5241 nm. Fur-a!Electronic mail: ydzheng@netra.nju.edu.cn3330003-6951/99/75(21)/3333/3/$15.00Downloaded 02 Apr 2013 to 165.106.222.195. This article is copyrighted as indicated in the abstractthermore, we discuss the possible mechanism of the PL fromthe oxidized Si12x2yGexCy thin films.The Si12x2yGexCy samples used in this work weregrown on Si ~100! substrates by plasma-enhanced chemicalvapor deposition ~PECVD!.15 The Si12x2yGexCy layers withthe thickness of 170 nm were deposited at 600 °C from si-lane, germane, and ethylene in a hydrogen carrier. Aftergrowth, the samples were wet oxidized at 1100 °C for 20min. In order to clarify the photoluminescence of the oxi-dized Si12x2yGexCy thin films, two different references wereused. One was the as-grown Si12x2yGexCy sample grownunder the same conditions and not experiencing wet oxida-tion process; the other was a cleaned silicon sample cut fromthe identical silicon wafer and wet oxidized under the samecondition as that of the oxidized Si12x2yGexCy samples.The composition of the Si12x2yGexCy thin films beforewet oxidation was determined using Auger electron spectros-copy ~AES!. The fraction of Si, Ge, and C in the films isabout 0.16, 0.70, and 0.14, respectively. X-ray diffraction~XRD! result shows that the thin films are polycrystalline.The oxidized Si12x2yGexCy thin films are amorphousaccording to the result of XRD. The chemical state and thecomposition of the oxidized Si12x2yGexCy films were deter-mined by x-ray photoelectron spectroscopy ~XPS!. XPS onthe Si12x2yGexCy samples was also measured for compari-son with oxidized Si12x2yGexCy films ~see Fig. 1!. Figure 1shows that for as-grown and oxidized Si12x2yGexCy films,the Si2p peak is at 99.0 ~attributed to Si in Si12x2yGexCy16!and 103.0 eV ~characteristic of SiO217!, respectively, and theGe3d peak is at 29.0 ~Ge in Si12x2yGexCy17! and 32.6 eV~Ge in GeO217!, respectively. The C1s peak is at 284.6 eV~C–C bonding17! for both as-grown and oxidized films. Thebinding energy of O1s for the oxidized films is 532.7 eV,attributed to O in the mixture of SiO2 and GeO2, which isreasonable because 532.7 eV is a little less than the standarddata for O1s in SiO2 533.0 eV.17 XPS results show that theoxidized film is mainly the mixture of SiO2 and GeO2, whichcan be represented by Si(12x)Ge(x)O2 for convenience.The ratio of the quantity of Si and Ge in the oxidizedSi12x2yGexCy films calculated from XPS, Si:Ge, is approxi-mately 1:0.3.The photoluminescence spectra of the samples were3 © 1999 American Institute of Physics. Reuse of AIP content is subject to the terms at: http://apl.aip.org/about/rights_and_permissions3334 Appl. Phys. Lett., Vol. 75, No. 21, 22 November 1999 Cheng et al.measured by an EG&G Fluoro Max-2 spectrophotometer atroom temperature ~300 K! and a Xe lamp was used for alight source. Figure 2 shows the PL spectrum from the oxi-dized Si12x2yGexCy sample under the excitation of l5241 nm. A luminescence band with a peak at about 393nm ~about 3.15 eV! was observed. The PL spectra of the tworeference samples, the as-grown Si12x2yGexCy sample andthe oxidized Si sample, were also measured, but neither ofFIG. 1. XPS spectra in the Si2p , Ge3d , C1s , and O1s region from theas-grown and the oxidized Si12x2yGexCy thin films on Si ~100!. ~a! Theas-grown Si12x2yGexCy thin films. ~b! The oxidized Si12x2yGexCy thinfilms.FIG. 2. Photoluminescence spectrum for the wet oxidized Si12x2yGexCythin film on Si ~100!.Downloaded 02 Apr 2013 to 165.106.222.195. This article is copyrighted as indicated in the abstractthem has photoluminescence under the same measurementcondition. In order to study the source of the luminescencefrom the oxidized Si12x2yGexCy sample, we measuredroom-temperature photoluminescence excitation ~PLE! spec-trum of the oxidized Si12x2yGexCy sample ~see Fig. 3!. Theexcitation peak is around 241 nm ~about 5.14 eV!.According to the work of Skuja et al.,10 the source of theblue luminescence in oxygen-deficient amorphous Si(12x)Ge(x)O2 is the twofold-coordinated silicon O–Si–O(Si20) or O–Ge–O (Ge20). The Si20~Ge20! defects contain twononbonding electrons which form a ground state singlet level(S0), an excited singlet level (S1), and a triple level (T1).The blue luminescence ~;3.1 eV! is attributed to the T1→S0 transition10 and it is excited in the region of the Ge-related optical absorption band peaking at 5.14 eV ~attributedto the S0→S1 transition!.10 From the data of XPS and XRD,we can reasonably consider the oxidized Si12x2yGexCy filmas oxygen-deficient amorphous Si(12x)Ge(x)O2 film(xEXP;23% from XPS!, among which there is still a littleamount of C left from the thermal oxidation process. Theexcitation peak at 5.14 eV in Fig. 3 is consistent to the S0→S1 transition of Si20~Ge20!, and the luminescence peak at3.15 eV in Fig. 2 is consistent to the T1→S0 transition ofSi20~Ge20!. So the observed luminescence band peaking atabout 393 nm from the oxidized Si12x2yGexCy sample inFig. 2 should arise from the twofold-coordinated siliconO–Si–O (Si20) or O–Ge–O (Ge20).We can explain the mechanism of the photolumines-cence from the oxidized Si12x2yGexCy sample in terms ofthe dipole model11 proposed by Ginzburg et al. According tothis model, we gave the energy level scheme of the Si20 de-fects in the oxidized Si12x2yGexCy thin films on Si~100!substrates ~see Fig. 4!. The photoexcited electrons, when de-localized and thermalized, disintegrated into two subsystems:the mobile electrons with energy E.EC (EC is the Mott mo-bility edge!, which are responsible for the radiative recombi-nation, and a system of localized electrons with energy E,EC , which setup a system of randomly distributed dipoles.Suffering scattering from randomly distributed dipoles, themobile electrons lose some energy D before recombination,FIG. 3. Photoluminescence excitation spectrum for the wet oxidizedSi12x2yGexCy on Si ~100!.. Reuse of AIP content is subject to the terms at: http://apl.aip.org/about/rights_and_permissions3335Appl. Phys. Lett., Vol. 75, No. 21, 22 November 1999 Cheng et al.where D depends on Ge concentration. From the formula E53.67120.74(12x)2 proposed by Ginzburg et al.,11 whereE53.15 eV from the result of PL measurement, we can es-timate the value of x in the oxygen-deficient amorphousSi(12x)Ge(x)O2 film as xTH;16%. Taking into accountthe error arising from the measurement of XPS, the theoreticdata is fairly consistent to the experimental data 23%.The behavior of C during the wet oxidation process ofthe thin films is very important to the formation of oxygen-deficient amorphous Si(12x)Ge(x)O2 film. Just aftergrowth and before wet oxidation, some C atoms are substi-tutional incorporated and make bonds with Si or Ge atoms.When the sample is wet oxidized at 1100 °C, most C atomsdepart from the thin film perhaps in the form of CO or CO2,leaving some nonbonding electrons in Si20~Ge20!. So, the sub-stitutional C atoms can improve the formation of the oxygendeficient defects.In summary, the Si12x2yGexCy thin films were grownon Si ~100! by PECVD and wet oxidized at 1100 °C for 20FIG. 4. An energy level scheme of the Si20 defect in the oxidizedSi12x2yGexCy thin film on Si ~100!.Downloaded 02 Apr 2013 to 165.106.222.195. This article is copyrighted as indicated in the abstractmin. The photoluminescence spectra of the thermally oxi-dized Si12x2yGexCy thin films measured at room tempera-ture show a photoluminescence band with a peak at ;393nm under the exciting radiation of l5241 nm. The photolu-minescence is related to the twofold-coordinated siliconO–Si–O (Si20) or O–Ge–O (Ge20) defects. The C atoms inthe films improve the formation of such defects during thewet oxidation process.This work was supported by National Science Fund ofChina and the Research Fund for the Doctoral Program ofHigher Education. The authors also acknowledge W. F.Chen, Y. D. Ye, and H. Chen for characterization assistance.1 L. T. Canham, Appl. Phys. Lett. 57, 1046 ~1990!.2 H. Takagi, H. Ogawa, Y. Yamazaki, A. Ishizaki, and Y. Kanemitsu, Appl.Phys. Lett. 56, 2349 ~1990!.3 Y. Maeda, N. Tsukamoto, Y. Yazawa, and Y. Kanemitsu, Appl. Phys.Lett. 59, 3168 ~1991!.4 Yoshihiko Kanemitsu, Thin Solid Films 276, 44 ~1996!.5 J. Yuan, D. Haneman, W. Li, and T. Zhang, Semicond. Sci. Technol. 13,130 ~1998!.6 T. Matsumoto, J. Takahashi, T. Tamaki, T. Futagi, H. Mimura, and Y.Kanemitsu, Appl. Phys. Lett. 64, 226 ~1994!.7 A. R. Silin and L. N. Skuja, J. Non-Cryst. Solids 71, 443 ~1985!.8 L. N. Skuja, A. N. Streketsky, and A. B. Pakovich, Solid State Commun.50, 1069 ~1984!.9 E. W. J. Mitchell and E. G. S. Page, Proc. Phys. Soc. London 67, 262~1954!.10 L. N. Skuja, A. N. Trukhin, and A. E. Plaudis, Phys. Status Solidi A 84,K153 ~1984!.11 L. P. Ginzburg, A. A. Gordeev, A. P. Gorchakov, and A. P. Jilinsky, J.Non-Cryst. Solids 183, 234 ~1995!.12 A. J. Cohen, Phys. Rev. 105, 1151 ~1957!.13 J. Yuan, D. Haneman, and I. Andrienko, The 24th International Confer-ence on the Physics of Semiconductors, Jerusalem, Israel, 1998 ~unpub-lished!, Vol. 2, Th-P206.14 K. Eberl, S. S. Iyer, S. Zollner, J. C. Tsang, and F. K. LeGoues, Appl.Phys. Lett. 60, 3033 ~1992!.15 Ning Jiang, L. Zang, R. L. Jiang, S. M. Zhu, P. Han, X. B. Liu, X. M.Cheng, R. H. Wang, Y. D. Zheng, X. N. Hu, and J. X. Fang, Appl. Phys.A: Solids Surf. 68, 457 ~1998!.16 M. Kim and H. J. Osten, Appl. Phys. Lett. 70, 2702 ~1997!.17 Handbook of X-ray Photoelectron Spectroscopy, edited by C. D. Wagner,W. M. Riggs, L. E. Davis, J. F. Moulder, and G. E. Muilenberg ~Perkin-Elmer, Physical Electronics Division, 1978!.. Reuse of AIP content is subject to the terms at: http://apl.aip.org/about/rights_and_permissions

Room-Temperature Blue Luminescence of Thermally Oxidized Si\u3csub\u3e1-x-y\u3c/sub\u3eGe\u3csub\u3ex\u3c/sub\u3eC\u3csub\u3ey\u3c/sub\u3e Thin Films on Si (100) Substrates

Scholarship;  Research;  and Creative Work at Bryn Mawr College

APPLIED PHYSICS LETTERS VOLUME 75, NUMBER 21 22 NOVEMBER 1999Room-temperature blue luminescence of thermally oxidized Si 12x 2yGexCy
thin films on Si „100… substrates
Xuemei Cheng, Youdou Zheng,a) Xiabing Liu, Lan Zang, Zhiyun Lo, Shunming Zhu, Ping
Han, and Ruolian Jiang
Physics Department, Nanjing University, China, 210093
~Received 24 May 1999; accepted for publication 28 September 1999!
We measured at room temperature the photoluminescence spectra of the thermally oxidized
Si12x2yGexCy thin films which were grown on silicon substrates by plasma-enhanced chemical
vapor deposition and then wet oxidized at 1100 °C for 20 min. The photoluminescence band with a
peak at;393 nm under the exciting radiation ofl5241 nm was observed. Possible mechanism of
this photoluminescence is discussed. ©1999 American Institute of Physics.
@S0003-6951~99!01147-X#d
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i-
e
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on
.
the
ri-
e
,
dard
d
i-
ereDuring the last few years, special interest has been
voted to the blue-green luminescence of silicon-based m
rials because they have potential for becoming novel
future photoelectric devices. Among them, silicon-based m
terials with nanostructures, such as porous silicon,1 xidized
silicon, and germanium nanocrystallites,2–5 oxidized SiC
nanocrystallites,6 and so on, are perhaps under the most w
and complete investigations. However, another import
type of silicon-based material luminescence, luminesce
related to oxygen-deficient defects in amorphous S2
films7–9 and Si(12x)Ge(x)O2 films,
10,11has been paid more
and more attention recently. Starting from Mitchell a
Page’s work,9 many other groups have worked in this fiel
Skuja8 proposed that the well-known optical absorption ba
at 5.03 eV and the luminescence band at 4.3 eV in am
phous SiO2 are due to singlet-to-singlet transitions, while t
luminescence band at 2.65 eV due to triplet-to-singlet tr
sitions in a silicon-related intrinsic defect, twofold coord
nated silicon Si2
0. A characteristic photoluminescence~PL!
band at 3.1 eV in oxygen deficient SiO2:GeO2 was also
observed.10,12 In 1995 Ginzburget al. proposed a physics
model based on the energy level arrangement of Si2
0~Ge2
0! to
explain some features of the blue luminescence in am
phous Si(12x)Ge(x)O2.
11 In addition, even for the cases o
the luminescence in the nanostructure materials, the oxy
deficient luminescent centers are often taken i
consideration.13
Recently, the studies on Si12x2yGexCy alloys have been
paid great attention because of the considerably greater
ibility, compared to that available in the Si12xGex /Si mate-
rial system, to control strain and electronic properties
group IV heterostructure materials. Substantial impro
ments in the growth and characterizing of Si12x2yGexCy al-
loys have already been achieved.14
In this letter, we report the photoluminescence spec
from the thermally oxidized Si12x2yGexCy thin films on Si
~100! showing a photoluminescence band with a peak
;393 nm under the exciting radiation ofl5241 nm. Fur-
a!Electronic mail: ydzheng@netra.nju.edu.cn3330003-6951/99/75(21)/3333/3/$15.00
Downloaded 02 Apr 2013 to 165.106.222.195. This article is copyrighted as indicated in the abstracte-
e-
d
-
e
t
ce
d
r-
-
r-
en
o
x-
n
-
a
t
thermore, we discuss the possible mechanism of the PL f
the oxidized Si12x2yGexCy thin films.
The Si12x2yGexCy samples used in this work wer
grown on Si~100! substrates by plasma-enhanced chem
vapor deposition~PECVD!.15 The Si12x2yGexCy layers with
the thickness of 170 nm were deposited at 600 °C from
lane, germane, and ethylene in a hydrogen carrier. A
growth, the samples were wet oxidized at 1100 °C for
min. In order to clarify the photoluminescence of the ox
dized Si12x2yGexCy thin films, two different references wer
used. One was the as-grown Si12x2yGexCy sample grown
under the same conditions and not experiencing wet ox
tion process; the other was a cleaned silicon sample cut f
the identical silicon wafer and wet oxidized under the sa
condition as that of the oxidized Si12x2yGexCy samples.
The composition of the Si12x2yGexCy thin films before
wet oxidation was determined using Auger electron spect
copy ~AES!. The fraction of Si, Ge, and C in the films i
about 0.16, 0.70, and 0.14, respectively. X-ray diffracti
~XRD! result shows that the thin films are polycrystalline
The oxidized Si12x2yGexCy thin films are amorphous
according to the result of XRD. The chemical state and
composition of the oxidized Si12x2yGexCy films were deter-
mined by x-ray photoelectron spectroscopy~XPS!. XPS on
the Si12x2yGexCy samples was also measured for compa
son with oxidized Si12x2yGexCy films ~see Fig. 1!. Figure 1
shows that for as-grown and oxidized Si12x2yGexCy films,
the Si2p peak is at 99.0~attributed to Si in Si12x2yGexCy
16!
and 103.0 eV~characteristic of SiO2
17!, respectively, and the
Ge3d peak is at 29.0~Ge in Si12x2yGexCy
17! and 32.6 eV
~Ge in GeO2
17!, respectively. The C1s peak is at 284.6 eV
~C–C bonding17! for both as-grown and oxidized films. Th
binding energy of O1s for the oxidized films is 532.7 eV
attributed to O in the mixture of SiO2 and GeO2, which is
reasonable because 532.7 eV is a little less than the stan
data for O1s in SiO2 533.0 eV.
17 XPS results show that the
oxidized film is mainly the mixture of SiO2 and GeO2, which
can be represented by Si(12x)Ge(x)O2 for convenience.
The ratio of the quantity of Si and Ge in the oxidize
Si12x2yGexCy films calculated from XPS, Si:Ge, is approx
mately 1:0.3.
The photoluminescence spectra of the samples w3 © 1999 American Institute of Physics
. Reuse of AIP content is subject to the terms at: http://apl.aip.org/about/rights_and_permissions
r
a
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3334 Appl. Phys. Lett., Vol. 75, No. 21, 22 November 1999 Cheng et al.measured by an EG&G Fluoro Max-2 spectrophotomete
room temperature~300 K! and a Xe lamp was used for
light source. Figure 2 shows the PL spectrum from the o
dized Si12x2yGexCy sample under the excitation ofl
5241 nm. A luminescence band with a peak at about 3
nm ~about 3.15 eV! was observed. The PL spectra of the tw
reference samples, the as-grown Si12x2yGexCy sample and
the oxidized Si sample, were also measured, but neithe
FIG. 1. XPS spectra in the Si2p , Ge3d , C1s , and O1s region from the
as-grown and the oxidized Si12x2yGexCy thin films on Si ~100!. ~a! The
as-grown Si12x2yGexCy thin films. ~b! The oxidized Si12x2yGexCy thin
films.
FIG. 2. Photoluminescence spectrum for the wet oxidized Si12x2yGexCy
thin film on Si ~100!.Downloaded 02 Apr 2013 to 165.106.222.195. This article is copyrighted as indicated in the abstractat
i-
3
of
them has photoluminescence under the same measure
condition. In order to study the source of the luminescen
from the oxidized Si12x2yGexCy sample, we measure
room-temperature photoluminescence excitation~PLE! spec-
trum of the oxidized Si12x2yGexCy sample~see Fig. 3!. The
excitation peak is around 241 nm~about 5.14 eV!.
According to the work of Skujaet al.,10 the source of the
blue luminescence in oxygen-deficient amorphous S
2x)Ge(x)O2 is the twofold-coordinated silicon O–Si–O
(Si2
0) or O–Ge–O (Ge2
0). The Si2
0~Ge2
0! defects contain two
nonbonding electrons which form a ground state singlet le
(S0), an excited singlet level (S1), and a triple level (T1).
The blue luminescence~;3.1 eV! is attributed to theT1
→S0 transition10 and it is excited in the region of the Ge
related optical absorption band peaking at 5.14 eV~attributed
to theS0→S1 transition!.10 From the data of XPS and XRD
we can reasonably consider the oxidized Si12x2yGexCy film
as oxygen-deficient amorphous Si(12x)Ge(x)O2 film
(xEXP;23% from XPS!, among which there is still a little
amount of C left from the thermal oxidation process. T
excitation peak at 5.14 eV in Fig. 3 is consistent to theS0
→S1 transition of Si20~Ge20!, and the luminescence peak
3.15 eV in Fig. 2 is consistent to theT1→S0 transition of
Si2
0~Ge2
0!. So the observed luminescence band peaking
about 393 nm from the oxidized Si12x2yGexCy sample in
Fig. 2 should arise from the twofold-coordinated silico
O–Si–O (Si2
0) or O–Ge–O (Ge2
0).
We can explain the mechanism of the photolumin
cence from the oxidized Si12x2yGexCy sample in terms of
the dipole model11 proposed by Ginzburget al.According to
this model, we gave the energy level scheme of the Si2
0 de-
fects in the oxidized Si12x2yGexCy thin films on Si~100!
substrates~see Fig. 4!. The photoexcited electrons, when d
localized and thermalized, disintegrated into two subsyste
the mobile electrons with energyE.EC (EC is the Mott mo-
bility edge!, which are responsible for the radiative recomb
nation, and a system of localized electrons with energyE
,EC , which setup a system of randomly distributed dipol
Suffering scattering from randomly distributed dipoles, t
mobile electrons lose some energyD before recombination,
FIG. 3. Photoluminescence excitation spectrum for the wet oxidi
Si12x2yGexCy on Si ~100!.. Reuse of AIP content is subject to the terms at: http://apl.aip.org/about/rights_and_permissions
es
s
t
et
o
n-
s
m
m
e
0
xi-
a-
on
he
of
of
F.
ce.
pl.
ys.
Y.
un.
J.
fer-
pl.
.
ys.
3335Appl. Phys. Lett., Vol. 75, No. 21, 22 November 1999 Cheng et al.whereD depends on Ge concentration. From the formulaE
53.67120.74(12x)2 proposed by Ginzburget al.,11 where
E53.15 eV from the result of PL measurement, we can
timate the value ofx in the oxygen-deficient amorphou
Si(12x)Ge(x)O2 film as xTH;16%. Taking into accoun
the error arising from the measurement of XPS, the theor
data is fairly consistent to the experimental data 23%.
The behavior of C during the wet oxidation process
the thin films is very important to the formation of oxyge
deficient amorphous Si(12x)Ge(x)O2 film. Just after
growth and before wet oxidation, some C atoms are sub
tutional incorporated and make bonds with Si or Ge ato
When the sample is wet oxidized at 1100 °C, most C ato
depart from the thin film perhaps in the form of CO or CO2,
leaving some nonbonding electrons in Si2
0~Ge2
0!. So, the sub-
stitutional C atoms can improve the formation of the oxyg
deficient defects.
In summary, the Si12x2yGexCy thin films were grown
on Si ~100! by PECVD and wet oxidized at 1100 °C for 2
FIG. 4. An energy level scheme of the Si2
0 defect in the oxidized
Si12x2yGexCy thin film on Si ~100!.Downloaded 02 Apr 2013 to 165.106.222.195. This article is copyrighted as indicated in the abstract-
ic
f
ti-
s.
s
n
min. The photoluminescence spectra of the thermally o
dized Si12x2yGexCy thin films measured at room temper
ture show a photoluminescence band with a peak at;393
nm under the exciting radiation ofl5241 nm. The photolu-
minescence is related to the twofold-coordinated silic
O–Si–O (Si2
0) or O–Ge–O (Ge2
0) defects. The C atoms in
the films improve the formation of such defects during t
wet oxidation process.
This work was supported by National Science Fund
China and the Research Fund for the Doctoral Program
Higher Education. The authors also acknowledge W.
Chen, Y. D. Ye, and H. Chen for characterization assistan
1L. T. Canham, Appl. Phys. Lett.57, 1046~1990!.
2H. Takagi, H. Ogawa, Y. Yamazaki, A. Ishizaki, and Y. Kanemitsu, Ap
Phys. Lett.56, 2349~1990!.
3Y. Maeda, N. Tsukamoto, Y. Yazawa, and Y. Kanemitsu, Appl. Ph
Lett. 59, 3168~1991!.
4Yoshihiko Kanemitsu, Thin Solid Films276, 44 ~1996!.
5J. Yuan, D. Haneman, W. Li, and T. Zhang, Semicond. Sci. Technol.13,
130 ~1998!.
6T. Matsumoto, J. Takahashi, T. Tamaki, T. Futagi, H. Mimura, and
Kanemitsu, Appl. Phys. Lett.64, 226 ~1994!.
7A. R. Silin and L. N. Skuja, J. Non-Cryst. Solids71, 443 ~1985!.
8L. N. Skuja, A. N. Streketsky, and A. B. Pakovich, Solid State Comm
50, 1069~1984!.
9E. W. J. Mitchell and E. G. S. Page, Proc. Phys. Soc. London67, 262
~1954!.
10L. N. Skuja, A. N. Trukhin, and A. E. Plaudis, Phys. Status Solidi A84,
K153 ~1984!.
11L. P. Ginzburg, A. A. Gordeev, A. P. Gorchakov, and A. P. Jilinsky,
Non-Cryst. Solids183, 234 ~1995!.
12A. J. Cohen, Phys. Rev.105, 1151~1957!.
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Room-Temperature Blue Luminescence of Thermally Oxidized Si\u3csub\u3e1-x-y\u3c/sub\u3eGe\u3csub\u3ex\u3c/sub\u3eC\u3csub\u3ey\u3c/sub\u3e Thin Films on Si (100) Substrates

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Scholarship; Research; and Creative Work at Bryn Mawr College