The growth of InGaAsN/GaAs multiple quantum well structures by metal-organic vapor phase epitaxy is monitored by in situ reflectometry. The nitrogen incorporation is found to depend superlinearly on the precursor flow and a threshold value for the flow is observed. By in situmeasurements of the InGaAsN quantum well samples with a fixed indium content, the change in the reflectance during the quantum wellgrowth is found to be linearly dependent on the quantum well nitrogen content. A model to determine the nitrogen content already during the growth is developed. Moreover, the field of application of in situ reflectance monitoring is extended from thick layers to thin layers, including quantum wells.Peer reviewe

Hakkarainen, T.

Knuuttila, L.

Lipsanen, Harri

Mattila, M.

Reentilä, O.

Sopanen, Markku

O. Reentilä

M. Mattila

L. Knuuttila

T. Hakkarainen

M. Sopanen

H. Lipsanen

Crossref

In situ

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This is an electronic reprint of the original article.
This reprint may differ from the original in pagination and typographic detail.
Author(s): Reentilä, O. & Mattila, M. & Knuuttila, L. & Hakkarainen, T. &
Sopanen, M. & Lipsanen, Harri
Title: In situ determination of nitrogen content in InGaAsN quantum wells
Year: 2006
Version: Final published version
Please cite the original version:
Reentilä, O. & Mattila, M. & Knuuttila, L. & Hakkarainen, T. & Sopanen, M. & Lipsanen,
Harri. 2006. In situ determination of nitrogen content in InGaAsN quantum wells. Journal
of Applied Physics. Volume 100, Issue 1. P. 013509/1-4. ISSN 0021-8979 (printed). DOI:
10.1063/1.2209772.
Rights: © 2006 American Institute of Physics. This article may be downloaded for personal use only. Any other use
requires prior permission of the author and the American Institute of Physics.
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In situ determination of nitrogen content in InGaAsN quantum wells
O. Reentilä, M. Mattila, L. Knuuttila, T. Hakkarainen, M. Sopanen, and H. Lipsanen 
 
Citation: Journal of Applied Physics 100, 013509 (2006); doi: 10.1063/1.2209772 
View online: http://dx.doi.org/10.1063/1.2209772 
View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/100/1?ver=pdfcov 
Published by the AIP Publishing 
 
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Appl. Phys. Lett. 102, 102110 (2013); 10.1063/1.4795623 
 
Utilizing the interface adsorption of nitrogen for the growth of high-quality GaInAsN/GaAs quantum wells by metal
organic chemical vapor deposition for near infrared applications 
Appl. Phys. Lett. 96, 141102 (2010); 10.1063/1.3360216 
 
Strain-induced nitrogen incorporation in atomic layer epitaxy growth of InAsN/GaAs quantum wells using metal
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In situ determination of nitrogen content in InGaAsN quantum wells
O. Reentilä,a M. Mattila, L. Knuuttila, T. Hakkarainen, M. Sopanen, and H. Lipsanen
Optoelectronics Laboratory, Micronova, Helsinki University of Technology, P.O. Box 3500,
FIN-02015 TKK, Finland
Received 27 March 2006; accepted 21 April 2006; published online 7 July 2006
The growth of InGaAsN/GaAs multiple quantum well structures by metal-organic vapor phase
epitaxy is monitored by in situ reflectometry. The nitrogen incorporation is found to depend
superlinearly on the precursor flow and a threshold value for the flow is observed. By in situ
measurements of the InGaAsN quantum well samples with a fixed indium content, the change in the
reflectance during the quantum well growth is found to be linearly dependent on the quantum well
nitrogen content. A model to determine the nitrogen content already during the growth is developed.
Moreover, the field of application of in situ reflectance monitoring is extended from thick layers to
thin layers, including quantum wells. © 2006 American Institute of Physics.
DOI: 10.1063/1.2209772
I. INTRODUCTION
The research of dilute nitrides has achieved a solid po-
sition in the research of compound semiconductors since
Kondow et al.1 published their results concerning the effects
of nitrogen on the properties of InGaAsN. It has been ob-
served that the adjustment of the nitrogen content and the
control of the material quality are demanding tasks both in
metal-organic vapor phase epitaxy MOVPE and in molecu-
lar beam epitaxy MBE. When growth processes are devel-
oped for these challenging materials the information ob-
tained during the growth by in situ monitoring is all the more
important. MOVPE and MBE systems both have the possi-
bility of in situ monitoring the growth by nondestructive
methods.
In situ reflectance measurements of MOVPE growth are
fast, easy, and practical way to monitor the progress of crys-
tal growth. They are commonly used to monitor the growth
of thick layers of III-N materials; see, for example, Hardtde-
gen et al.2 The in situ monitoring of the growth of thick
GaAs and AlAs layers has also been studied.3 However, it is
also possible to monitor the growth of thin layers, e.g., quan-
tum wells QWs,4 and the layers can even be partially ana-
lyzed during the growth.5 Here we use in situ reflectance
measurements to monitor the MOVPE growth of InGaAsN
quantum wells. Furthermore, a model to determine the QW
nitrogen content during the growth is derived.
II. EXPERIMENT
The samples were fabricated by low-pressure close
coupled showerhead MOVPE system at 100 torr pressure on
semi-insulating 100 GaAs substrates using hydrogen H2
as a carrier gas. The total flow to the reactor was 6 l /min.
Trimethylindium TMIn, trimethylgallium TMGa, tertiary-
butylarsine TBAs, and dimethylhydrazine DMHy were
used as precursors for indium, gallium, arsenic, and nitrogen,
respectively. Two GaAs buffer layers, the first one at 660 °C
and the second at 575 °C thermocouple readings, were
grown on the 350-m-thick substrate before the QW struc-
ture which consisted of four InGaAsN/GaAs QWs. The
growth temperature of the QW structure was 575 °C. The
QW and barrier thicknesses were approximately 8 and
15 nm, respectively. No extra capping was used on top of the
uppermost barrier layer. TMGa, TMIn, and TBAs molar
flows to the reactor were kept constant for all the samples.
TBAs/III molar flow ratio for all the QWs was 2.23 while the
DMHy molar flow to the reactor was varied from
0 to 1680 mol/min DMHy/III molar flow ratios are 0–37,
DMHy/V ratios are 0–0.94 to fabricate samples with differ-
ent nitrogen contents.
In situ monitoring of the growth was realized with a
normal incident reflectance setup using a halogen lamp as a
light source. The rotation speed of 100 rpm of the susceptor
led to a sampling frequency of 1.7 Hz. In our system, the
reflected signal can be recorded at either 635 or 950 nm. In
this study, the reflectance was measured at 635 nm.
The layer thicknesses, indium contents, and nitrogen
contents of the QWs were determined by high-resolution
x-ray diffraction XRD measurements -2 configuration
and simulations together with photoluminescence PL mea-
surements and band anticrossing BAC model.6 Combining
the information obtained from these methods the nitrogen
content of the samples was found to vary from 0% to 5%.
The indium content was 16.5%–19%. Both low temperature
photoluminescence LTPL 10 K and room temperature
photoluminescence RTPL measurements were carried out
to determine the luminescence energy and optical quality of
the samples. Ex situ atmospheric pressure MOVPE annealing
using TBAs to protect the surface from desorption was per-
formed for 10 min at 700 °C to enhance the PL intensity of
the samples. LTPL and RTPL measurements were performed
for as-grown samples as well as for the annealed samples.
III. RESULTS AND DISCUSSION
Figure 1 shows the QW nitrogen content as a function of
the DMHy molar flow. The nitrogen content has been re-aElectronic mail: outi.reentila@tkk.fi
JOURNAL OF APPLIED PHYSICS 100, 013509 2006
0021-8979/2006/1001/013509/4/$23.00 © 2006 American Institute of Physics100, 013509-1
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ported earlier to have a superlinear dependence on the
amount of nitrogen precursor in the vapor phase.7 A nonlin-
ear correlation between the QW nitrogen content and the
DMHy molar flow can also be seen in Fig. 1. In addition, a
clear threshold for the nitrogen incorporation is observed as
the DMHy flow is increased. The threshold DMHy flow ap-
pears to be around 850 mol/min. Below this value the ni-
trogen incorporation is relatively inefficient.
A typical XRD curve and a simulation fitted to that are
shown in Fig. 2. XRD measurements were performed on
as-grown samples to avoid any possible changes in the QW
material and intermixing at the QW-barrier interfaces. In the
simulated sample in Fig. 2, the QWs contained 19% indium
and 0.8% nitrogen. The quantum well thickness was 8.6 nm.
Good agreement between the measurement and simulation
curves was found for all the samples. At large nitrogen con-
tents the intensity of the satellite peaks in the XRD curve
decreased which indicates a slight decrease of the crystal
quality.
Figure 3 shows RTPL and LTPL peak energies from the
as-grown and annealed samples as a function of the DMHy
molar flow. The PL peak energies vary nonlinearly from
0.79 to 1.27 eV depending on the DMHy flow and thus the
QW nitrogen content Fig. 1. To excite the as-grown
samples sufficiently, a large pump power was needed. This,
however, led to blueshift of the luminescence wavelength.
Blueshift increased up to 35 nm as the luminescence wave-
length increased. This is assumed to be caused by increasing
compositional inhomogeneity within the quantum wells as
the nitrogen content increases. No LTPL was observed from
the sample grown with the largest DMHy molar flow.
Figure 4 shows a typical reflectance curve measured dur-
ing the growth of the quantum well structure. QW growth
regions shaded in the figure can be clearly distinguished
from the barriers. The sample in Fig. 4 contained 5% nitro-
gen and 16.5% indium in all four 7-nm-thick quantum wells
separated by 16-nm-thick barrier layers. All the samples
FIG. 1. QW nitrogen content as a function of DMHy flow. The curve indi-
cates a threshold for nitrogen incorporation with a DMHy flow of about
850 mol/min.
FIG. 2. Typical XRD measurement upper curve and a simulation result
lower curve fitted to the measurement. For clarity, a vertical offset is added
between the measured and simulated curves.
FIG. 3. RTPL and LTPL peak energies of as-grown and annealed samples as
a function of the DMHy molar flow.
FIG. 4. Reflectance measured during the QW structure growth. QW growth
regions are shaded and the unmarked regions between them are barrier
growth regions. The linear fit to the reflectance measured during the growth
of the first QW is also shown.
013509-2 Reentilä et al. J. Appl. Phys. 100, 013509 2006
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showed similar consistent behavior in in situ reflectance
measurements. We have earlier observed that the deteriora-
tion of the crystal quality of the QW can be observed as
changes in the in situ reflectance curve.5 Thus, the fact that
all the samples fabricated here showed a similar shape of the
in situ reflectance curves indicates a successful growth of the
structures even with large nitrogen contents. The good crys-
talline quality was also confirmed by the XRD measure-
ments.
The changes in the reflectance in Fig. 4 originate from
the different complex refractive indices of GaAs and In-
GaAsN. Also, a change in temperature can cause variations
in reflectance, but here the whole QW stack was grown at a
constant temperature. Naturally, the refractive index of In-
GaAsN depends on the nitrogen and indium contents: the
increase of both leads to a larger refractive index difference
between GaAs and the QW. The reflectance increases as the
QW is grown and decreases during the barrier growth. A
linear fit to the reflectance measured during the growth of the
first QW is shown in Fig. 4 and has a slope R /t of 3.0
10−4 1 /s. Because the difference of reflectance R is lin-
early dependent on the layer thickness as the first approxi-
mation when the layer is thin, the slope R /t is linearly
dependent on the growth rate. The first QW has been chosen
to be the one of interest because of simplicity: below the first
QW there is only a thick layer of GaAs, whereas below the
subsequent QWs there are also the other QWs already
grown.
Figure 5 shows the growth rate corrected reflectance
slopes R /d of the samples with different nitrogen con-
tents in the QWs. The slopes in Fig. 5 are obtained in units of
1/nm by taking the slopes R /t in 1/s and dividing
them with the actual QW growth rates. After the growth rate
correction the slope R /d depends only on the composi-
tion of the quantum well. The slope increases linearly with
the QW nitrogen content assuming that the QW indium con-
tent is constant. A linear fit forced via the InGaAs data point
is shown in the figure with a slope of 1.3010−4 1 /
% nm. The deviations from the fit are assumed to be
caused mostly by the slightly different QW indium contents
of the samples. The samples grown with the smallest DMHy
molar flows contain two percentage units more indium than
the sample grown with the largest DMHy molar flow. As a
result, the data points for the three samples with small nitro-
gen content remain a bit above the linear fit in Fig. 5.
In the light of these results we report that for a given
indium content, the nitrogen content y of the InGaAsN QW
can be written as
y =
kInGaAsN − kInGaAs
A
, 1
where ki is the reflectance slope R /d from material i, and
A is a constant. A can be determined from the linear fit to the
growth rate corrected slope R /d as a function of the QW
nitrogen content. We expect this method to be suitable for
any fixed indium content. For In0.18Ga0.82AsN, A is 1.30
10−4 1 / % nm and kInGaAs is 4.6510−4 1 /nm. For a
given indium composition, kInGaAs and A are constants and,
therefore, the nitrogen content can be determined straightfor-
wardly from the in situ data.
In situ reflectance provides information about the sample
composition and quality5 which makes it a fast and easy to
use tool for characterizing dilute nitride QW samples already
during the fabrication of the sample. We would like to point
out that thick layers are not needed, but a layer thickness of
a few nanometers is enough to enable the use of in situ
reflectance to determine the composition. In addition to the
dilute nitride samples investigated here and in Ref. 5, the
method should be applicable to any material combination
with different refractive indices. We are currently in the pro-
cess of expanding the model to include all the QWs in the
structure and not only the first QW. Then the homogeneity of
the structure in the vertical direction, e.g., the similarity of
the QWs in the multi-quantum-well MQW structure, could
also be observed during the growth.
IV. CONCLUSION
MOVPE growth of InGaAsN/GaAs MQW structures
has been monitored using in situ reflectance measurements.
XRD characterization together with PL measurements has
been performed and the BAC model is utilized to determine
the QW nitrogen content. Based on the measurements and
simulations, a clear thresholdlike behavior of the QW nitro-
gen content as a function of DMHy molar flow was ob-
served. Furthermore, the nitrogen content of the
InGaAsN/GaAs quantum wells with a fixed indium content
is found to be linearly dependent on the slope of the in situ
reflectance measured during the quantum well growth. Based
on these results, we have developed a method to determine
the nitrogen content of quantum wells in situ from the reflec-
tance curve measured during the growth in the MOVPE re-
actor. The model developed in this study is applicable to the
typical nitrogen content range for dilute nitrides from 0% to
5% and extends the field of application of the reflectance
monitoring to include the growth of thin layers.
FIG. 5. Growth rate corrected slopes R /d of the reflectance measured
during the growth of the first QW as a function of the QW nitrogen content.
A linear fit forced via the InGaAs data point gives a slope of 1.30
10−4 1 / % nm.
013509-3 Reentilä et al. J. Appl. Phys. 100, 013509 2006
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130.233.216.27 On: Wed, 06 May 2015 09:19:01
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English

In situ determination of nitrogen content in InGaAsN quantum wells

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): Reentilä, O. & Mattila, M. & Knuuttila, L. & Hakkarainen, T. &Sopanen, M. & Lipsanen, HarriTitle: In situ determination of nitrogen content in InGaAsN quantum wellsYear: 2006Version: Final published versionPlease cite the original version:Reentilä, O. & Mattila, M. & Knuuttila, L. & Hakkarainen, T. & Sopanen, M. & Lipsanen,Harri. 2006. In situ determination of nitrogen content in InGaAsN quantum wells. Journalof Applied Physics. Volume 100, Issue 1. P. 013509/1-4. ISSN 0021-8979 (printed). DOI:10.1063/1.2209772.Rights: © 2006 American Institute of Physics. This article may be downloaded for personal use only. Any other userequires prior permission 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)In situ determination of nitrogen content in InGaAsN quantum wellsO. Reentilä, M. Mattila, L. Knuuttila, T. Hakkarainen, M. Sopanen, and H. Lipsanen  Citation: Journal of Applied Physics 100, 013509 (2006); doi: 10.1063/1.2209772 View online: http://dx.doi.org/10.1063/1.2209772 View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/100/1?ver=pdfcov Published by the AIP Publishing  Articles you may be interested in Atomic scale investigations of ultra-thin GaInN/GaN quantum wells with high indium content Appl. Phys. Lett. 102, 102110 (2013); 10.1063/1.4795623  Utilizing the interface adsorption of nitrogen for the growth of high-quality GaInAsN/GaAs quantum wells by metalorganic chemical vapor deposition for near infrared applications Appl. Phys. Lett. 96, 141102 (2010); 10.1063/1.3360216  Strain-induced nitrogen incorporation in atomic layer epitaxy growth of InAsN/GaAs quantum wells using metalorganic chemical vapor deposition Appl. Phys. Lett. 95, 051102 (2009); 10.1063/1.3193663  In situ determination of InGaAs and GaAsN composition in multiquantum-well structures J. Appl. Phys. 101, 033533 (2007); 10.1063/1.2435065  Simultaneous determination of indium and nitrogen contents of InGaAsN quantum wells by optical in situmonitoring Appl. Phys. Lett. 89, 231919 (2006); 10.1063/1.2402265    [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: Wed, 06 May 2015 09:19:01In situ determination of nitrogen content in InGaAsN quantum wellsO. Reentilä,a M. Mattila, L. Knuuttila, T. Hakkarainen, M. Sopanen, and H. LipsanenOptoelectronics Laboratory, Micronova, Helsinki University of Technology, P.O. Box 3500,FIN-02015 TKK, FinlandReceived 27 March 2006; accepted 21 April 2006; published online 7 July 2006The growth of InGaAsN/GaAs multiple quantum well structures by metal-organic vapor phaseepitaxy is monitored by in situ reflectometry. The nitrogen incorporation is found to dependsuperlinearly on the precursor flow and a threshold value for the flow is observed. By in situmeasurements of the InGaAsN quantum well samples with a fixed indium content, the change in thereflectance during the quantum well growth is found to be linearly dependent on the quantum wellnitrogen content. A model to determine the nitrogen content already during the growth is developed.Moreover, the field of application of in situ reflectance monitoring is extended from thick layers tothin layers, including quantum wells. © 2006 American Institute of Physics.DOI: 10.1063/1.2209772I. INTRODUCTIONThe research of dilute nitrides has achieved a solid po-sition in the research of compound semiconductors sinceKondow et al.1 published their results concerning the effectsof nitrogen on the properties of InGaAsN. It has been ob-served that the adjustment of the nitrogen content and thecontrol of the material quality are demanding tasks both inmetal-organic vapor phase epitaxy MOVPE and in molecu-lar beam epitaxy MBE. When growth processes are devel-oped for these challenging materials the information ob-tained during the growth by in situ monitoring is all the moreimportant. MOVPE and MBE systems both have the possi-bility of in situ monitoring the growth by nondestructivemethods.In situ reflectance measurements of MOVPE growth arefast, easy, and practical way to monitor the progress of crys-tal growth. They are commonly used to monitor the growthof thick layers of III-N materials; see, for example, Hardtde-gen et al.2 The in situ monitoring of the growth of thickGaAs and AlAs layers has also been studied.3 However, it isalso possible to monitor the growth of thin layers, e.g., quan-tum wells QWs,4 and the layers can even be partially ana-lyzed during the growth.5 Here we use in situ reflectancemeasurements to monitor the MOVPE growth of InGaAsNquantum wells. Furthermore, a model to determine the QWnitrogen content during the growth is derived.II. EXPERIMENTThe samples were fabricated by low-pressure closecoupled showerhead MOVPE system at 100 torr pressure onsemi-insulating 100 GaAs substrates using hydrogen H2as a carrier gas. The total flow to the reactor was 6 l /min.Trimethylindium TMIn, trimethylgallium TMGa, tertiary-butylarsine TBAs, and dimethylhydrazine DMHy wereused as precursors for indium, gallium, arsenic, and nitrogen,respectively. Two GaAs buffer layers, the first one at 660 °Cand the second at 575 °C thermocouple readings, weregrown on the 350-m-thick substrate before the QW struc-ture which consisted of four InGaAsN/GaAs QWs. Thegrowth temperature of the QW structure was 575 °C. TheQW and barrier thicknesses were approximately 8 and15 nm, respectively. No extra capping was used on top of theuppermost barrier layer. TMGa, TMIn, and TBAs molarflows to the reactor were kept constant for all the samples.TBAs/III molar flow ratio for all the QWs was 2.23 while theDMHy molar flow to the reactor was varied from0 to 1680 mol/min DMHy/III molar flow ratios are 0–37,DMHy/V ratios are 0–0.94 to fabricate samples with differ-ent nitrogen contents.In situ monitoring of the growth was realized with anormal incident reflectance setup using a halogen lamp as alight source. The rotation speed of 100 rpm of the susceptorled to a sampling frequency of 1.7 Hz. In our system, thereflected signal can be recorded at either 635 or 950 nm. Inthis study, the reflectance was measured at 635 nm.The layer thicknesses, indium contents, and nitrogencontents of the QWs were determined by high-resolutionx-ray diffraction XRD measurements -2 configurationand simulations together with photoluminescence PL mea-surements and band anticrossing BAC model.6 Combiningthe information obtained from these methods the nitrogencontent of the samples was found to vary from 0% to 5%.The indium content was 16.5%–19%. Both low temperaturephotoluminescence LTPL 10 K and room temperaturephotoluminescence RTPL measurements were carried outto determine the luminescence energy and optical quality ofthe samples. Ex situ atmospheric pressure MOVPE annealingusing TBAs to protect the surface from desorption was per-formed for 10 min at 700 °C to enhance the PL intensity ofthe samples. LTPL and RTPL measurements were performedfor as-grown samples as well as for the annealed samples.III. RESULTS AND DISCUSSIONFigure 1 shows the QW nitrogen content as a function ofthe DMHy molar flow. The nitrogen content has been re-aElectronic mail: outi.reentila@tkk.fiJOURNAL OF APPLIED PHYSICS 100, 013509 20060021-8979/2006/1001/013509/4/$23.00 © 2006 American Institute of Physics100, 013509-1 [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: Wed, 06 May 2015 09:19:01ported earlier to have a superlinear dependence on theamount of nitrogen precursor in the vapor phase.7 A nonlin-ear correlation between the QW nitrogen content and theDMHy molar flow can also be seen in Fig. 1. In addition, aclear threshold for the nitrogen incorporation is observed asthe DMHy flow is increased. The threshold DMHy flow ap-pears to be around 850 mol/min. Below this value the ni-trogen incorporation is relatively inefficient.A typical XRD curve and a simulation fitted to that areshown in Fig. 2. XRD measurements were performed onas-grown samples to avoid any possible changes in the QWmaterial and intermixing at the QW-barrier interfaces. In thesimulated sample in Fig. 2, the QWs contained 19% indiumand 0.8% nitrogen. The quantum well thickness was 8.6 nm.Good agreement between the measurement and simulationcurves was found for all the samples. At large nitrogen con-tents the intensity of the satellite peaks in the XRD curvedecreased which indicates a slight decrease of the crystalquality.Figure 3 shows RTPL and LTPL peak energies from theas-grown and annealed samples as a function of the DMHymolar flow. The PL peak energies vary nonlinearly from0.79 to 1.27 eV depending on the DMHy flow and thus theQW nitrogen content Fig. 1. To excite the as-grownsamples sufficiently, a large pump power was needed. This,however, led to blueshift of the luminescence wavelength.Blueshift increased up to 35 nm as the luminescence wave-length increased. This is assumed to be caused by increasingcompositional inhomogeneity within the quantum wells asthe nitrogen content increases. No LTPL was observed fromthe sample grown with the largest DMHy molar flow.Figure 4 shows a typical reflectance curve measured dur-ing the growth of the quantum well structure. QW growthregions shaded in the figure can be clearly distinguishedfrom the barriers. The sample in Fig. 4 contained 5% nitro-gen and 16.5% indium in all four 7-nm-thick quantum wellsseparated by 16-nm-thick barrier layers. All the samplesFIG. 1. QW nitrogen content as a function of DMHy flow. The curve indi-cates a threshold for nitrogen incorporation with a DMHy flow of about850 mol/min.FIG. 2. Typical XRD measurement upper curve and a simulation resultlower curve fitted to the measurement. For clarity, a vertical offset is addedbetween the measured and simulated curves.FIG. 3. RTPL and LTPL peak energies of as-grown and annealed samples asa function of the DMHy molar flow.FIG. 4. Reflectance measured during the QW structure growth. QW growthregions are shaded and the unmarked regions between them are barriergrowth regions. The linear fit to the reflectance measured during the growthof the first QW is also shown.013509-2 Reentilä et al. J. Appl. Phys. 100, 013509 2006 [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: Wed, 06 May 2015 09:19:01showed similar consistent behavior in in situ reflectancemeasurements. We have earlier observed that the deteriora-tion of the crystal quality of the QW can be observed aschanges in the in situ reflectance curve.5 Thus, the fact thatall the samples fabricated here showed a similar shape of thein situ reflectance curves indicates a successful growth of thestructures even with large nitrogen contents. The good crys-talline quality was also confirmed by the XRD measure-ments.The changes in the reflectance in Fig. 4 originate fromthe different complex refractive indices of GaAs and In-GaAsN. Also, a change in temperature can cause variationsin reflectance, but here the whole QW stack was grown at aconstant temperature. Naturally, the refractive index of In-GaAsN depends on the nitrogen and indium contents: theincrease of both leads to a larger refractive index differencebetween GaAs and the QW. The reflectance increases as theQW is grown and decreases during the barrier growth. Alinear fit to the reflectance measured during the growth of thefirst QW is shown in Fig. 4 and has a slope R /t of 3.010−4 1 /s. Because the difference of reflectance R is lin-early dependent on the layer thickness as the first approxi-mation when the layer is thin, the slope R /t is linearlydependent on the growth rate. The first QW has been chosento be the one of interest because of simplicity: below the firstQW there is only a thick layer of GaAs, whereas below thesubsequent QWs there are also the other QWs alreadygrown.Figure 5 shows the growth rate corrected reflectanceslopes R /d of the samples with different nitrogen con-tents in the QWs. The slopes in Fig. 5 are obtained in units of1/nm by taking the slopes R /t in 1/s and dividingthem with the actual QW growth rates. After the growth ratecorrection the slope R /d depends only on the composi-tion of the quantum well. The slope increases linearly withthe QW nitrogen content assuming that the QW indium con-tent is constant. A linear fit forced via the InGaAs data pointis shown in the figure with a slope of 1.3010−4 1 /% nm. The deviations from the fit are assumed to becaused mostly by the slightly different QW indium contentsof the samples. The samples grown with the smallest DMHymolar flows contain two percentage units more indium thanthe sample grown with the largest DMHy molar flow. As aresult, the data points for the three samples with small nitro-gen content remain a bit above the linear fit in Fig. 5.In the light of these results we report that for a givenindium content, the nitrogen content y of the InGaAsN QWcan be written asy =kInGaAsN − kInGaAsA, 1where ki is the reflectance slope R /d from material i, andA is a constant. A can be determined from the linear fit to thegrowth rate corrected slope R /d as a function of the QWnitrogen content. We expect this method to be suitable forany fixed indium content. For In0.18Ga0.82AsN, A is 1.3010−4 1 / % nm and kInGaAs is 4.6510−4 1 /nm. For agiven indium composition, kInGaAs and A are constants and,therefore, the nitrogen content can be determined straightfor-wardly from the in situ data.In situ reflectance provides information about the samplecomposition and quality5 which makes it a fast and easy touse tool for characterizing dilute nitride QW samples alreadyduring the fabrication of the sample. We would like to pointout that thick layers are not needed, but a layer thickness ofa few nanometers is enough to enable the use of in situreflectance to determine the composition. In addition to thedilute nitride samples investigated here and in Ref. 5, themethod should be applicable to any material combinationwith different refractive indices. We are currently in the pro-cess of expanding the model to include all the QWs in thestructure and not only the first QW. Then the homogeneity ofthe structure in the vertical direction, e.g., the similarity ofthe QWs in the multi-quantum-well MQW structure, couldalso be observed during the growth.IV. CONCLUSIONMOVPE growth of InGaAsN/GaAs MQW structureshas been monitored using in situ reflectance measurements.XRD characterization together with PL measurements hasbeen performed and the BAC model is utilized to determinethe QW nitrogen content. Based on the measurements andsimulations, a clear thresholdlike behavior of the QW nitro-gen content as a function of DMHy molar flow was ob-served. Furthermore, the nitrogen content of theInGaAsN/GaAs quantum wells with a fixed indium contentis found to be linearly dependent on the slope of the in situreflectance measured during the quantum well growth. Basedon these results, we have developed a method to determinethe nitrogen content of quantum wells in situ from the reflec-tance curve measured during the growth in the MOVPE re-actor. The model developed in this study is applicable to thetypical nitrogen content range for dilute nitrides from 0% to5% and extends the field of application of the reflectancemonitoring to include the growth of thin layers.FIG. 5. Growth rate corrected slopes R /d of the reflectance measuredduring the growth of the first QW as a function of the QW nitrogen content.A linear fit forced via the InGaAs data point gives a slope of 1.3010−4 1 / % nm.013509-3 Reentilä et al. J. Appl. Phys. 100, 013509 2006 [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: Wed, 06 May 2015 09:19:011M. Kondow, K. Uomi, A. Niva, T. Kitatani, S. Watahiki, and Y. Yasawa,Jpn. J. Appl. Phys., Part 1 35, 1273 1996.2H. Hardtdegen, N. Kaluza, R. Schmidt, R. Steins, E. V. Yakolev, R. Tala-laev, Y. N. Makarov, and J.-T. Zettler, Phys. Status Solidi A 201, 3122004.3A. Rebey, M. Habchi, A. Bchetnia, and B. El Jani, J. Cryst. Growth 261,450 2004.4R. Lum, J. McDonald, J. Bean, J. Vandenberg, T. Pernell, S. Chu, A.Robertson, and A. Karp, Appl. Phys. Lett. 69, 928 1996.5O. Reentilä, M. Mattila, M. Sopanen, and H. Lipsanen, J. Cryst. Growth290, 345 2006.6W. Shan, W. Walukiewicz, J. Ager, E. Haller, J. Geisz, D. Friedman, J.Olson, and S. Kurtz, Phys. Rev. Lett. 82, 1221 1999.7T. Miyamoto, T. Kageyama, S. Makino, D. Schlenker, F. Koyama, and K.Iga, J. Cryst. Growth 209, 339 2000.013509-4 Reentilä et al. J. Appl. Phys. 100, 013509 2006 [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: Wed, 06 May 2015 09:19:01

The growth of InGaAsN∕GaAs multiple quantum well structures by metal-organic vapor phase epitaxy is monitored by in situ reflectometry. The nitrogen incorporation is found to depend superlinearly on the precursor flow and a threshold value for the flow is observed. By in situ measurements of the InGaAsN quantum well samples with a fixed indium content, the change in the reflectance during the quantum well growth is found to be linearly dependent on the quantum well nitrogen content. A model to determine the nitrogen content already during the growth is developed. Moreover, the field of application of in situ reflectance monitoring is extended from thick layers to thin layers, including quantum wells.Peer reviewe

Reentilä, Outi

Mattila, Marco

Knuuttila, Lauri

Hakkarainen, Teppo

Journal of Applied Physics

In-situ determination of nitrogen content in InGaAsN quantum wells

https://aaltodoc.aalto.fi/bitstream/handle/123456789/15913/A1_reentil%c3%a4_o_2006.pdf?sequence=1&isAllowed=y

In situ determination of nitrogen content in InGaAsN quantum wells

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