Positron annihilation spectroscopy was used to study GaAsN/GaAs epilayers. GaAsN layers were found to contain Ga vacancies in defect complexes. The density of the vacancy complexes increases rapidly to the order of 1018 cm−3 with increasing N composition and decreases after annealing at 700 °C. The anticorrelation of the vacancy concentration and the integrated photoluminescence intensity suggests that the Ga vacancy complexes act as nonradiative recombination centers.Peer reviewe

Hakkarainen, T.

Lipsanen, Harri

Oila, J.

Saarinen, K.

Sopanen, Markku

Toivonen, J.

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Author(s): Toivonen, J. & Hakkarainen, T. & Sopanen, M. & Lipsanen, Harri &
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Title: Observation of defect complexes containing Ga vacancies in GaAsN
Year: 2003
Version: Final published version
Please cite the original version:
Toivonen, J. & Hakkarainen, T. & Sopanen, M. & Lipsanen, Harri & Oila, J. & Saarinen,
K. 2003. Observation of defect complexes containing Ga vacancies in GaAsN. Applied
Physics Letters. Volume 82, Issue 1. P. 40-42. ISSN 0003-6951 (printed). DOI:
10.1063/1.1533843.
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permission of the author and the American Institute of Physics. http://scitation.aip.org/content/aip/journal/jap
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Observation of defect complexes containing Ga vacancies in GaAsN
J. Toivonen, T. Hakkarainen, M. Sopanen, H. Lipsanen, J. Oila, and K. Saarinen 
 
Citation: Applied Physics Letters 82, 40 (2003); doi: 10.1063/1.1533843 
View online: http://dx.doi.org/10.1063/1.1533843 
View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/82/1?ver=pdfcov 
Published by the AIP Publishing 
 
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Observation of defect complexes containing Ga vacancies in GaAsN
J. Toivonen,a) T. Hakkarainen, M. Sopanen, and H. Lipsanen
Optoelectronics Laboratory, Helsinki University of Technology, P.O. Box 3500, FIN-02015 HUT, Finland
J. Oila and K. Saarinen
Laboratory of Physics, Helsinki University of Technology, P.O. Box 1100, FIN-02015 HUT, Finland
~Received 15 April 2002; accepted 7 November 2002!
Positron annihilation spectroscopy was used to study GaAsN/GaAs epilayers. GaAsN layers were
found to contain Ga vacancies in defect complexes. The density of the vacancy complexes increases
rapidly to the order of 1018 cm23 with increasing N composition and decreases after annealing at
700 °C. The anticorrelation of the vacancy concentration and the integrated photoluminescence
intensity suggests that the Ga vacancy complexes act as nonradiative recombination
centers. © 2003 American Institute of Physics. @DOI: 10.1063/1.1533843#
Quaternary alloy Ga12yInyNxAs12x is a novel material
for low-band-gap applications on gallium arsenide.1,2 The al-
loy is lattice matched to GaAs when y’3x , and only a few
percent of N (x,0.05) is needed to decrease the band gap
below 1 eV due to huge band-gap bowing. This material is
used in applications such as infrared lasers,3 multijunction
solar cells,4 and heterojunction bipolar transistors.5 Because
of the large size mismatch between As and N atoms, high
quality arsenide-nitride alloys are difficult to fabricate. The
epitaxial growth is typically performed at the temperature
range of 400 to 600 °C. The effects caused by N are more
straightforward to study with the ternary alloy GaAs12xNx .
The addition of N affects the band structure of GaAsN
mainly by decreasing the conduction band edge. However,
also the valence band changes a little, and it has been re-
cently shown that GaAsN/GaAs material system has type-I
band alignment.6,7 Various defects are formed in the material
during the growth, and post-growth annealing can be used to
eliminate some of them.8,9 Intrinsic point defects identified in
the arsenide-nitrides so far are an AsGa antisite,10,11 an N
interstitial,12–14 and a Ga vacancy.14
In this work, we have found evidence of vacancies in
GaAsN alloy grown by metalorganic vapor phase epitaxy
~MOVPE!. We show these vacancies to be Ga vacancies
(VGa) that exist in defect complexes. We have further studied
the effect of annealing on the density of the Ga vacancies.
Positron annihilation spectroscopy15 was used to detect
vacancy-type defects in GaAsN epitaxial layers. A variable-
energy positron beam was used to scan the depth profile.
Positrons thermalize very fast in the sample and diffuse until
they annihilate with electrons. At room temperature, posi-
trons are effectively trapped by neutral and negatively-
charged vacancy defects. The annihilation spectrum of
trapped positrons differs from that of free positrons by
smaller Doppler broadening of the annihilation line at 511
keV. Broadening is described by line shape parameters S and
W determined as a fraction of counts in the central area and
the wing area of the peak, respectively.15 Thus, vacancies are
detected as an increase in the low-momentum parameter S
and a decrease in the high-momentum parameter W . The
measurement is sensitive in the vacancy density range ap-
proximately from 1016 to 1019 cm23.
The GaAsN layers were grown by MOVPE on semi-
insulating GaAs ~001! substrates using TMGa, TBAs, and
DMHy precursors and hydrogen carrier gas. A detailed de-
scription of the growth parameters can be found in Ref. 16.
The samples consist of a 50-nm-thick GaAs buffer, a
GaAs12xNx layer with a thickness of 170 nm and composi-
tion x ranging from 0 to 0.05, and a 3-nm-thick GaAs cap
layer. One of the samples was cut in pieces, which were
annealed in the MOVPE reactor for 10 min under different
annealing conditions. The GaAsN layer thicknesses and
compositions were determined by high-resolution x-ray dif-
fraction using ~004! reflection, and photoluminescence ~PL!
at a temperature of 10 K was used to characterize the optical
quality of the layers. The unintentionally doped epilayers
were p-type with hole concentrations between 1016 and
1017 cm23 as determined by Hall measurements. The hole
concentration decreased with increasing N composition, and
the effect of annealing to the hole concentrations was negli-
gible.
When nitrogen is introduced into the GaAsN epilayer, an
increase in the S parameter and a decrease in the W param-
eter are observed at positron incident energies of 0 to 5 keV,
indicating the presence of vacancy defects in the 170-nm-
thick overlayer ~Fig. 1!. By increasing the nitrogen compo-
sition x of the GaAs12xNx layer higher than 1%, the value of
the S parameter saturates. A p-type GaAs sample was used to
obtain the reference levels SB50.5374 and WB50.0361 for
the GaAs lattice.
The linear dependency between the S and W parameters
in our as-grown GaAsN epilayers ~Fig. 2! shows that the
change in the positron annihilation signal is caused by only a
single type of a vacancy.15 To identify this defect, we com-
pare the slopes of the (S , W) data to those expected for VGa
and VAs . The parameters of SV ,Ga /SB51.019 and
WV ,Ga /WB50.76 were estimated for Ga vacancies by mea-
suring the highly Si-doped and Si d-doped GaAs samples,
where complexes of VGa have been previously identified.17,18
The parameters for neutral As vacancies have been estimated
to be SV ,As /SB51.030 and WV ,As /WB50.80.19 The (S , W)
points of GaAsN layers appear between the values of GaAsa!Electronic mail: juha.toivonen@hut.fi
APPLIED PHYSICS LETTERS VOLUME 82, NUMBER 1 6 JANUARY 2003
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lattice and Ga vacancy, which allows us to identify the de-
fects as Ga vacancies. In fact, As vacancies are not typically
seen by positron annihilation spectroscopy in p-type and
semi-insulating GaAs, because of their positive charge.15
According to electron irradiation studies, isolated Ga va-
cancies are not stable in the GaAs lattice at temperatures
above 300 °C.20 Thus, the vacancies in our samples grown at
.500 °C probably belong to defect complexes with some
other defects or impurities. The C and H impurity concentra-
tions in MOVPE-grown GaInNAs are typically
1017– 1018 cm23 and 1018– 1020 cm23,8,21 respectively.
However, the complex of VGa and C impurity is unlikely due
to the negative charge of both of them and vacancies deco-
rated by hydrogen are usually not positron traps.22
Molecular-beam-epitaxy-grown GaAsN has been shown to
contain interstitial nitrogen (Ni).12–14 However, we consider
it unlikely that complexes of Ni and VGa could be stable,
since the N interstitials could easily annihilate the Ga va-
cancy. The AsGa antisite is another typical defect arising at
group-V-rich growth conditions, and it has already been
identified in GaAsN.10,11 Indeed, the densities of positive
AsGa and negative VGa have been found to correlate in As-
rich low-temperature-grown GaAs,23 suggesting that they
form neutral complexes.24 We thus infer that the complexes
involving VGa constitute intrinsic defects, and their likely
assignment is that formed of the acceptor VGa and donor
antisites such as AsGa or NGa .
The vacancy concentration of an epilayer can be esti-
mated by applying a positron trapping model with a single
type of vacancies.15 Figure 3 shows the experimental VGa
concentration and the integrated PL intensity at 10 K of the
GaAsN samples. The VGa concentration increases with N
composition up to the order of 1018 cm23. Interestingly, the
VGa concentration anticorrelates with the intensity of the
photoluminescence.
A post-growth thermal annealing process is typically
used to enhance the optical quality of the arsenide-nitrides.
Figure 4 shows the S parameter data of the GaAs0.975N0.025
layers annealed at different conditions. Annealing at 650 °C
decreases the S parameter and the sample annealed at 700 °C
exhibits an even more pronounced effect. The S parameter,
however, remains high compared with the vacancy-free level
SB .
Figure 5 shows the PL efficiency and the VGa concentra-
FIG. 1. Low-momentum parameter S as a function of positron incident
energy in the as-grown GaAs12xNx samples. The reference value SB of
p-type GaAs and the characteristic value SV of the VGa are drawn by dashed
lines. The top axis shows the mean depth of positron penetration corre-
sponding to the positron incident energy.
FIG. 2. High-momentum parameter W as a function of low-momentum
parameter S for as-grown GaAs12xNx samples. Characteristic W and S pa-
rameters for VAs ~h! and VGa ~n! are from Refs. 18 and 22, respectively,
and parameters for VGa ~,! are measured in this work. The dashed lines are
guides for the eye.
FIG. 3. Integrated PL intensity at 10 K and VGa concentration of as-grown
170-nm-thick GaAs12xNx epilayers as a function of N composition.
FIG. 4. Low-momentum parameter S as a function of positron incident
energy in GaAs0.975N0.025 samples annealed at different temperatures. Other
features are identical with Fig. 1.
41Appl. Phys. Lett., Vol. 82, No. 1, 6 January 2003 Toivonen et al.
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tion of GaAs0.975N0.025 annealed at different temperatures.
The maximum PL efficiency is obtained by annealing for 10
min at 700 °C under H2 carrier gas flow and TBAs excess
ambient in the MOVPE reactor.16,25 This procedure reduces
the VGa density by a factor of 5 compared to that found in
as-grown material. The ratio between the VGa concentration
and the PL intensity is about the same as in the as-grown
GaAsN layers with increasing N composition. The anticorre-
lation of the VGa density and the PL intensity thus suggests
that the defect complexes containing the Ga vacancies act as
nonradiative recombination centers in GaAsN.
In summary, we have found vacancies in MOVPE-
grown GaAsN that are attributed to Ga vacancies in defect
complexes. The density of the vacancies was found to in-
crease rapidly up to the order of 1018 cm23 with increasing
N composition, and to decrease by a factor of 5 after the
thermal annealing procedure optimized for the PL intensity.
The anticorrelation between the vacancy density and the in-
tegrated PL intensity suggest that the defect complex acts as
a nonradiative recombination center.
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FIG. 5. Integrated PL intensity at 10 K and VGa concentration of 170-nm-
thick GaAs0.975N0.025 epilayers annealed at different conditions. The lines are
guides to the eye.
42 Appl. Phys. Lett., Vol. 82, No. 1, 6 January 2003 Toivonen et al.
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English

Observation of defect complexes containing Ga vacancies in GaAsN

Aaltodoc Publication Archive

This is an electronic reprint of the original article.This reprint may differ from the original in pagination and typographic detail.Author(s): Toivonen, J. & Hakkarainen, T. & Sopanen, M. & Lipsanen, Harri &Oila, J. & Saarinen, K.Title: Observation of defect complexes containing Ga vacancies in GaAsNYear: 2003Version: Final published versionPlease cite the original version:Toivonen, J. & Hakkarainen, T. & Sopanen, M. & Lipsanen, Harri & Oila, J. & Saarinen,K. 2003. Observation of defect complexes containing Ga vacancies in GaAsN. AppliedPhysics Letters. Volume 82, Issue 1. P. 40-42. ISSN 0003-6951 (printed). DOI:10.1063/1.1533843.Rights: © 2003 AIP Publishing. This article may be downloaded for personal use only. Any other use requires priorpermission of the author and the American Institute of Physics. http://scitation.aip.org/content/aip/journal/japAll material supplied via Aaltodoc is protected by copyright and other intellectual property rights, andduplication or sale of all or part of any of the repository collections is not permitted, except that material maybe duplicated by you for your research use or educational purposes in electronic or print form. You mustobtain permission for any other use. Electronic or print copies may not be offered, whether for sale orotherwise to anyone who is not an authorised user.Powered by TCPDF (www.tcpdf.org)Observation of defect complexes containing Ga vacancies in GaAsNJ. Toivonen, T. Hakkarainen, M. Sopanen, H. Lipsanen, J. Oila, and K. Saarinen  Citation: Applied Physics Letters 82, 40 (2003); doi: 10.1063/1.1533843 View online: http://dx.doi.org/10.1063/1.1533843 View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/82/1?ver=pdfcov Published by the AIP Publishing  Articles you may be interested in Vacancy-type defects in Er-doped GaN studied by a monoenergetic positron beam J. Appl. Phys. 103, 104505 (2008); 10.1063/1.2932166  Low-temperature emission in dilute GaAsN alloys grown by metalorganic vapor phase epitaxy J. Appl. Phys. 103, 063526 (2008); 10.1063/1.2901141  Effect of growth rate and gallium source on GaAsN Appl. Phys. Lett. 82, 2634 (2003); 10.1063/1.1565500  Comparison of the annealing characteristics of resistivity and vacancy defects for implant isolated n-type GaAs J. Appl. Phys. 87, 663 (2000); 10.1063/1.371923  Effect of reactive ion etching on the yellow luminescence of GaN Appl. Phys. Lett. 75, 3710 (1999); 10.1063/1.125437    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:130.233.216.27 On: Mon, 04 May 2015 10:17:19Observation of defect complexes containing Ga vacancies in GaAsNJ. Toivonen,a) T. Hakkarainen, M. Sopanen, and H. LipsanenOptoelectronics Laboratory, Helsinki University of Technology, P.O. Box 3500, FIN-02015 HUT, FinlandJ. Oila and K. SaarinenLaboratory of Physics, Helsinki University of Technology, P.O. Box 1100, FIN-02015 HUT, Finland~Received 15 April 2002; accepted 7 November 2002!Positron annihilation spectroscopy was used to study GaAsN/GaAs epilayers. GaAsN layers werefound to contain Ga vacancies in defect complexes. The density of the vacancy complexes increasesrapidly to the order of 1018 cm23 with increasing N composition and decreases after annealing at700 °C. The anticorrelation of the vacancy concentration and the integrated photoluminescenceintensity suggests that the Ga vacancy complexes act as nonradiative recombinationcenters. © 2003 American Institute of Physics. @DOI: 10.1063/1.1533843#Quaternary alloy Ga12yInyNxAs12x is a novel materialfor low-band-gap applications on gallium arsenide.1,2 The al-loy is lattice matched to GaAs when y’3x , and only a fewpercent of N (x,0.05) is needed to decrease the band gapbelow 1 eV due to huge band-gap bowing. This material isused in applications such as infrared lasers,3 multijunctionsolar cells,4 and heterojunction bipolar transistors.5 Becauseof the large size mismatch between As and N atoms, highquality arsenide-nitride alloys are difficult to fabricate. Theepitaxial growth is typically performed at the temperaturerange of 400 to 600 °C. The effects caused by N are morestraightforward to study with the ternary alloy GaAs12xNx .The addition of N affects the band structure of GaAsNmainly by decreasing the conduction band edge. However,also the valence band changes a little, and it has been re-cently shown that GaAsN/GaAs material system has type-Iband alignment.6,7 Various defects are formed in the materialduring the growth, and post-growth annealing can be used toeliminate some of them.8,9 Intrinsic point defects identified inthe arsenide-nitrides so far are an AsGa antisite,10,11 an Ninterstitial,12–14 and a Ga vacancy.14In this work, we have found evidence of vacancies inGaAsN alloy grown by metalorganic vapor phase epitaxy~MOVPE!. We show these vacancies to be Ga vacancies(VGa) that exist in defect complexes. We have further studiedthe effect of annealing on the density of the Ga vacancies.Positron annihilation spectroscopy15 was used to detectvacancy-type defects in GaAsN epitaxial layers. A variable-energy positron beam was used to scan the depth profile.Positrons thermalize very fast in the sample and diffuse untilthey annihilate with electrons. At room temperature, posi-trons are effectively trapped by neutral and negatively-charged vacancy defects. The annihilation spectrum oftrapped positrons differs from that of free positrons bysmaller Doppler broadening of the annihilation line at 511keV. Broadening is described by line shape parameters S andW determined as a fraction of counts in the central area andthe wing area of the peak, respectively.15 Thus, vacancies aredetected as an increase in the low-momentum parameter Sand a decrease in the high-momentum parameter W . Themeasurement is sensitive in the vacancy density range ap-proximately from 1016 to 1019 cm23.The GaAsN layers were grown by MOVPE on semi-insulating GaAs ~001! substrates using TMGa, TBAs, andDMHy precursors and hydrogen carrier gas. A detailed de-scription of the growth parameters can be found in Ref. 16.The samples consist of a 50-nm-thick GaAs buffer, aGaAs12xNx layer with a thickness of 170 nm and composi-tion x ranging from 0 to 0.05, and a 3-nm-thick GaAs caplayer. One of the samples was cut in pieces, which wereannealed in the MOVPE reactor for 10 min under differentannealing conditions. The GaAsN layer thicknesses andcompositions were determined by high-resolution x-ray dif-fraction using ~004! reflection, and photoluminescence ~PL!at a temperature of 10 K was used to characterize the opticalquality of the layers. The unintentionally doped epilayerswere p-type with hole concentrations between 1016 and1017 cm23 as determined by Hall measurements. The holeconcentration decreased with increasing N composition, andthe effect of annealing to the hole concentrations was negli-gible.When nitrogen is introduced into the GaAsN epilayer, anincrease in the S parameter and a decrease in the W param-eter are observed at positron incident energies of 0 to 5 keV,indicating the presence of vacancy defects in the 170-nm-thick overlayer ~Fig. 1!. By increasing the nitrogen compo-sition x of the GaAs12xNx layer higher than 1%, the value ofthe S parameter saturates. A p-type GaAs sample was used toobtain the reference levels SB50.5374 and WB50.0361 forthe GaAs lattice.The linear dependency between the S and W parametersin our as-grown GaAsN epilayers ~Fig. 2! shows that thechange in the positron annihilation signal is caused by only asingle type of a vacancy.15 To identify this defect, we com-pare the slopes of the (S , W) data to those expected for VGaand VAs . The parameters of SV ,Ga /SB51.019 andWV ,Ga /WB50.76 were estimated for Ga vacancies by mea-suring the highly Si-doped and Si d-doped GaAs samples,where complexes of VGa have been previously identified.17,18The parameters for neutral As vacancies have been estimatedto be SV ,As /SB51.030 and WV ,As /WB50.80.19 The (S , W)points of GaAsN layers appear between the values of GaAsa!Electronic mail: juha.toivonen@hut.fiAPPLIED PHYSICS LETTERS VOLUME 82, NUMBER 1 6 JANUARY 2003400003-6951/2003/82(1)/40/3/$20.00 © 2003 American Institute of Physics 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:130.233.216.27 On: Mon, 04 May 2015 10:17:19lattice and Ga vacancy, which allows us to identify the de-fects as Ga vacancies. In fact, As vacancies are not typicallyseen by positron annihilation spectroscopy in p-type andsemi-insulating GaAs, because of their positive charge.15According to electron irradiation studies, isolated Ga va-cancies are not stable in the GaAs lattice at temperaturesabove 300 °C.20 Thus, the vacancies in our samples grown at.500 °C probably belong to defect complexes with someother defects or impurities. The C and H impurity concentra-tions in MOVPE-grown GaInNAs are typically1017– 1018 cm23 and 1018– 1020 cm23,8,21 respectively.However, the complex of VGa and C impurity is unlikely dueto the negative charge of both of them and vacancies deco-rated by hydrogen are usually not positron traps.22Molecular-beam-epitaxy-grown GaAsN has been shown tocontain interstitial nitrogen (Ni).12–14 However, we considerit unlikely that complexes of Ni and VGa could be stable,since the N interstitials could easily annihilate the Ga va-cancy. The AsGa antisite is another typical defect arising atgroup-V-rich growth conditions, and it has already beenidentified in GaAsN.10,11 Indeed, the densities of positiveAsGa and negative VGa have been found to correlate in As-rich low-temperature-grown GaAs,23 suggesting that theyform neutral complexes.24 We thus infer that the complexesinvolving VGa constitute intrinsic defects, and their likelyassignment is that formed of the acceptor VGa and donorantisites such as AsGa or NGa .The vacancy concentration of an epilayer can be esti-mated by applying a positron trapping model with a singletype of vacancies.15 Figure 3 shows the experimental VGaconcentration and the integrated PL intensity at 10 K of theGaAsN samples. The VGa concentration increases with Ncomposition up to the order of 1018 cm23. Interestingly, theVGa concentration anticorrelates with the intensity of thephotoluminescence.A post-growth thermal annealing process is typicallyused to enhance the optical quality of the arsenide-nitrides.Figure 4 shows the S parameter data of the GaAs0.975N0.025layers annealed at different conditions. Annealing at 650 °Cdecreases the S parameter and the sample annealed at 700 °Cexhibits an even more pronounced effect. The S parameter,however, remains high compared with the vacancy-free levelSB .Figure 5 shows the PL efficiency and the VGa concentra-FIG. 1. Low-momentum parameter S as a function of positron incidentenergy in the as-grown GaAs12xNx samples. The reference value SB ofp-type GaAs and the characteristic value SV of the VGa are drawn by dashedlines. The top axis shows the mean depth of positron penetration corre-sponding to the positron incident energy.FIG. 2. High-momentum parameter W as a function of low-momentumparameter S for as-grown GaAs12xNx samples. Characteristic W and S pa-rameters for VAs ~h! and VGa ~n! are from Refs. 18 and 22, respectively,and parameters for VGa ~,! are measured in this work. The dashed lines areguides for the eye.FIG. 3. Integrated PL intensity at 10 K and VGa concentration of as-grown170-nm-thick GaAs12xNx epilayers as a function of N composition.FIG. 4. Low-momentum parameter S as a function of positron incidentenergy in GaAs0.975N0.025 samples annealed at different temperatures. Otherfeatures are identical with Fig. 1.41Appl. Phys. Lett., Vol. 82, No. 1, 6 January 2003 Toivonen et al. 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:130.233.216.27 On: Mon, 04 May 2015 10:17:19tion of GaAs0.975N0.025 annealed at different temperatures.The maximum PL efficiency is obtained by annealing for 10min at 700 °C under H2 carrier gas flow and TBAs excessambient in the MOVPE reactor.16,25 This procedure reducesthe VGa density by a factor of 5 compared to that found inas-grown material. The ratio between the VGa concentrationand the PL intensity is about the same as in the as-grownGaAsN layers with increasing N composition. The anticorre-lation of the VGa density and the PL intensity thus suggeststhat the defect complexes containing the Ga vacancies act asnonradiative recombination centers in GaAsN.In summary, we have found vacancies in MOVPE-grown GaAsN that are attributed to Ga vacancies in defectcomplexes. The density of the vacancies was found to in-crease rapidly up to the order of 1018 cm23 with increasingN composition, and to decrease by a factor of 5 after thethermal annealing procedure optimized for the PL intensity.The anticorrelation between the vacancy density and the in-tegrated PL intensity suggest that the defect complex acts asa nonradiative recombination center.1 M. Weyers, M. Sato, and H. Ando, Jpn. J. Appl. Phys. 31, L853 ~1992!.2 M. Kondow, K. Uomi, A. Niwa, T. Kitatani, S. Watahiki, and Y. Yazawa,Jpn. J. Appl. Phys. 35, 1273 ~1996!.3 M. Fischer, D. Gollub, and A. Forchel, Jpn. J. Appl. Phys. 41, 1162~2002!.4 D. J. Friedman, J. F. Geisz, S. R. Kurtz, and J. M. Olson, J. Cryst. Growth195, 409 ~1998!.5 P. C. Chang, A. G. Baca, N. Y. Li, P. R. Sharps, H. Q. Hou, J. R. Laroche,and F. Ren, Appl. Phys. Lett. 76, 2788 ~2000!.6 A. Buyanova, G. Pozina, P. N. Hai, W. M. Chen, H. P. Xin, and C. W. Tu,Phys. Rev. B 63, 033303 ~2000!.7 P. Krispin, S. G. Spruytte, J. S. Harris, and K. 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Sopanen, and H. Lipsanen, J. Cryst.Growth 221, 456 ~2000!.17 T. Laine, K. Saarinen, J. Ma¨kinen, P. Hautoja¨rvi, C. Corbel, L. N. Pfeiffer,and P. H. Citrin, Phys. Rev. B 54, 11050 ~1996!.18 T. Laine, K. Saarinen, J. Ma¨kinen, P. Hautoja¨rvi, C. Corbel, M. J. Ashwin,and R. C. Newman, Appl. Phys. Lett. 71, 1843 ~1997!.19 R. Ambigapathy, A. A. Manuel, P. Hautoja¨rvi, K. Saarinen, and C. Corbel,Phys. Rev. B 50, 2188 ~1994!; J. Gebauer, R. Krause-Rehberg, C. Domke,Ph. Ebert, K. Urban, and T. Staab, Phys. Rev. B 63, 045203 ~2001!.20 C. Corbel, F. Pierre, K. Saarinen, P. Hautoja¨rvi, and P. Moser, Phys. Rev.B 45, 3386 ~1992!.21 A. Moto, M. Takahashi, and S. Takagishi, J. Cryst. Growth 221, 485~2000!.22 K. Saarinen, P. Hautoja¨rvi, J. Keinonen, E. Rauhala, J. Ra¨isa¨nen, and C.Corbel, Phys. Rev. B 43, 4249 ~1991!.23 T. Laine, K. Saarinen, P. Hautoja¨rvi, C. Corbel, and M. Missous, J. Appl.Phys. 86, 1888 ~1999!.24 M. Luysberg, H. Sohn, A. Prasad, P. Specht, Z. Liliental-Weber, E. R.Weber, J. Gebauer, and R. Krause-Rehberg, J. Appl. Phys. 83, 561 ~1998!.25 T. Hakkarainen, J. Toivonen, M. Sopanen, and H. Lipsanen, J. Cryst.Growth 234, 631 ~2002!.FIG. 5. Integrated PL intensity at 10 K and VGa concentration of 170-nm-thick GaAs0.975N0.025 epilayers annealed at different conditions. The lines areguides to the eye.42 Appl. Phys. Lett., Vol. 82, No. 1, 6 January 2003 Toivonen et al. 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:130.233.216.27 On: Mon, 04 May 2015 10:17:19

J. Toivonen

T. Hakkarainen

M. Sopanen

H. Lipsanen

J. Oila

K. Saarinen

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Observation of defect complexes containing Ga vacancies in GaAsN

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