Structural and optical properties of strain-compensated GaAsSb/GaAs quantum wells
with high Sb composition
X. H. Zheng, D. S. Jiang, S. Johnson, and Y. H. Zhang
Citation: Applied Physics Letters 83, 4149 (2003); doi: 10.1063/1.1628395
View online: http://dx.doi.org/10.1063/1.1628395
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APPLIED PHYSICS LETTERS

VOLUME 83, NUMBER 20

17 NOVEMBER 2003

Structural and optical properties of strain-compensated GaAsSbÕGaAs
quantum wells with high Sb composition
X. H. Zhenga)
Institute of Physics, Chinese Academy of Sciences, P.O. Box 603, Beijing 100080,
People’s Republic of China

D. S. Jiang
State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors,
Chinese Academy of Sciences, P.O. Box 912, Beijing 100083, People’s Republic of China

S. Johnson and Y. H. Zhang
Department of Electrical Engineering and Center for Solid State Electronics Research,
Arizona State University, Tempe, Arizona 85287-6206

共Received 28 July 2003; accepted 23 September 2003兲
The structural and optical properties of GaAsSb/GaAs quantum wells 共QWs兲 and
strain-compensated GaAsP/GaAs/GaAsSb/GaAs/GaAsP QWs grown on a GaAs substrate by
molecular beam epitaxy are investigated using high-resolution x-ray diffraction and
photoluminescence 共PL兲 measurements. We demonstrated that the insertion of tensile GaAsP layers
into the active region of GaAsSb/GaAs QWs effectively improves the structural and optical quality.
Even the Sb composition is as high as 0.39. The PL spectra at 11 K and room temperature indicate
that the PL peak of strain-compensated QWs has a narrower linewidth and higher intensity in
comparison to the sample without strain compensation. The results of PL peak blueshift with
increasing excitation show the strain-compensated GaAsSb/GaAs interface characteristic of type-I
band alignment. © 2003 American Institute of Physics. 关DOI: 10.1063/1.1628395兴

The prospect of realizing 1.3 ␮m laser device structures
on a GaAs substrate has attracted considerable interest because of the important applications in fiber-optics communications, photodiodes, data links, and optical interconnection.1– 4 For vertical cavity surface-emitting lasers, the
active region structures, which can be epitaxially grown on a
GaAs substrate, are of special technical interest. For this purpose, one promising candidate is the GaAsSb quantum well
共QW兲 structure. However, the critical layer thickness of
GaAsSb is limited5,6 due to its large lattice mismatch with
GaAs substrates and the higher composition of Sb in
GaAsSb/GaAs QW is normally hard to be available for highquality device structures. Moreover, a poor electron confinement due to a type-II interface and a small band offset becomes an obvious drawback and will result in a low
characteristic T 0 temperature.7 In order to compensate for the
compressive strain in GaAsSb/GaAs QWs and improve the
confinement effects of electrons, additional tensile GaAsP
barrier layers had been proposed to incorporate in the active
region to form a strain-compensated coupled QW
structure.7–9 However, the detailed structural and optical
properties as introducing the GaAsP tensile-compensation
layers are still not reported. In this letter, we performed highresolution x-ray diffraction 共HRXRD兲 and low-temperature
photoluminescence 共PL兲 measurements for both straincompensated and uncompensated GaAsSb/GaAs QWs structure, indicating that the insertion of strain-compensated
GaAsP layers effectively improves the structural quality at a
very high Sb composition in GaAs1⫺x Sbx layer up to 0.39. In
a兲

Electronic mail: elfiecn@yahoo.com.cn

addition, the PL peak of related strain-compensated QW
structures shows narrower linewidth and higher intensity, as
well as a remarkable redshift of the peak position.
The GaAsSb/GaAs QW and strain-compensated
GaAsSb/GaAs/GaAsP QW structures were grown by molecular beam epitaxy on a semi-insulating 共100兲 GaAs substrate. The growth details have been described elsewhere.8
The samples studied here are three period GaAsSb/GaAs
QWs 共B325兲 and five period strain-compensated GaAsSb/
GaAs/GaAsP QWs 共B344兲, respectively. Their growth structures of one period QW are schematically shown in Fig. 1. It
is noted that a higher number of QW periods were grown for
the B344 in order to check the effect of strain-compensation
on the structural and optical properties of multiple QWs.
HRXRD and reciprocal space mapping 共RSM兲 experiments
were performed using a Bede D1 triple-axis diffractometer
with a parabolic graded multiplayer Gutman mirror collimator, followed by a four-bounce channel-cut Si 共220兲 mono-

FIG. 1. Schematic energy band diagram of one growth period for 共a兲 the
normal GaAsSb/GaAs QWs and 共b兲 the strain-compensated GaAsP/GaAs/
GaAsSb/GaAs/GaAsP QWs with nominal thickness.

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4149
© 2003 American Institute of Physics
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Zheng et al.

Appl. Phys. Lett., Vol. 83, No. 20, 17 November 2003

FIG. 3. 共a兲 The symmetric 共004兲 and 共b兲 asymmetric 共224兲 RSMs of the
normal GaAsSb/GaAs QWs and strain-compensated GaAsP/GaAs/GaAsSb/
GaAs/GaAsP QWs, respectively.

mogeneity would decrease the phase coherence and eliminate the Pendellösung fringes.12 In addition, as can be seen in
Fig. 2, the distances between the zero-order satellite peak
and GaAs substrate peak for sample B344 are closer than
FIG. 2. The ␻ –2␪ scan profiles of 共004兲 reflection for B325 共up side兲 and
B344 共down side兲 showing the measurement and simulation, respectively.
that of B325. This result provides convincing evidence that
‘‘A’’ marks the envelope modulation induced by GaAsSb layer. Note that the
tensile GaAsP layers help to reduce the overall strain in mulPendellösung fringes among satellite peaks in the top left inset for B344 can
tiple QW structures.
be clearly seen.
To further investigate the structural properties of the
QWs, HR-RSM measurements around the symmetric 共004兲
chromator, delivering a Cu K ␣ 1 line of wavelength
and asymmetric 共224兲 were performed, displayed in Fig. 3.
␭⫽0.154 056 nm. The asymmetric two-bounce Si 共220兲 anaIn the 共004兲 RSM, the intensity maximum of the GaAs sublyzer crystal was placed in front of the detector. PL spectra
strate and SL peaks of the QW system are aligned along the
measurements were carried out by the He-Ne laser line
line ␻⫽␪, confirming that the QWs have grown on axis to
共␭⫽632.8 nm兲 excitation with a power intensity.
the GaAs substrate. However, it is worth noting that the
Figure 2 shows the experimental 共004兲 x-ray diffraction
asymmetric 共224兲 RSM for B325 and B344 is different. For
patterns of samples B325 and B344. The measured ␻ –2␪
B344, the diffraction peak of GaAs substrates and satellite
diffraction patterns were simulated using a computer propeaks are aligned in a vertical line 共dashed line兲 parallel to
gram based on dynamical theory.10,11 The strongest peaks are
the Q(004) or Q z axis, indicating that the straindue to the GaAs substrates. A series of sharp satellite peaks
compensated GaAsSb QWs are grown coherently on GaAs.
appear, modulated by several slow-varying envelopes. DisTherefore, the QWs system is fully strained, showing that the
tinct higher orders of satellite peaks can be observed, indiassumption of totally strained GaAsSb layers used in the
cating that the two multiple QW samples have good periodsimulation procedure to estimate Sb composition is justified.
icity and high quality. The QW period was determined from
For B325, a clear in-plane shift 共marked PR兲 of the QW
the distance of the satellite peaks. Their periods are 432 and
system with respect to the GaAs is observed, which corre238 Å, respectively. According to the best fit to the experisponds to a partial relaxation of about 30%. The inclined line
mental curves, we obtained sublayer thickness as well as Sb
共marked CR兲 shows a completely relaxed QW structure. The
and P composition. For B344, the Sb composition is up to
partial relaxation considered also complies with our assump0.39. These results show that the composition and thickness
tion of simulation program. The results are in agreement with
were successfully controlled, as was expected. However, it
those of ␻ –2␪ scans.
should be noted that Pendellösung fringes can be clearly seen
To check the optical properties of QWs, PL measurein the insets of Fig. 2 for sample B344, i.e., the strainments were performed. Figure 4 shows PL spectra of
compensated GaAsSb/GaAs QW where tensile GaAsP barsamples B325 and B344 at 11 K and RT, respectively. The 11
rier layers are added. Three fringes between every two neighK PL results show that the linewidth is reduced by over a
boring satellite peaks correspond well to the five periods of
factor of 2 for sample B344, from 54 to 25 meV, where
QW structures in the active region. It means that the added
tensile-strained GaAsP barrier layers are added. The lineGaAsP layers effectively compensate the compressive strain
width of B344 also decreases compared to that of B325 at
in GaAsSb/GaAs QWs and improve the interface quality,
RT. A reduced inhomogeneous broadening of the PL lineThis 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:
since any interface imperfection or compositional inhowidth, due to lateral composition and thickness modulation,
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Zheng et al.

Appl. Phys. Lett., Vol. 83, No. 20, 17 November 2003

4151

FIG. 5. PL peak shift as a function of the excitation power at T⫽11 K for
B325 共solid squares兲 and B344 共solid circles兲. The much larger blueshift for
B325 is characteristic of type-II QWs. The line is a guide for the eyes.

FIG. 4. PL spectra of normal GaAsSb/GaAs QWs 共B325兲 and straincompensated GaAsP/GaAs/GaAsSb/GaAs/GaAsP QWs 共B344兲 at 11 K 共dot
lines兲 and room temperature 共solid lines兲.

In conclusion, we investigated the structural and optical
properties of the normal GaAsSb/GaAs QWs and straincompensated GaAsP/GaAs/GaAsSb/GaAs/GaAsP QWs using HRXRD and PL. The interface quality becomes higher
and the clearer Pendellösung fringes are observed for straincompensated GaAsSb QWs. The asymmetrical 共224兲 RSM
measurements give us evidence that the GaAsSb base layers
remain fully elastic despite the high composition of Sb, up to
0.39 when the tensile layers GaAsP are added to the QW
structure, while the normal GaAsSb/GaAs QWs appears to
have partial relaxation of about 30%. The narrower linewidth
and higher intensity of the PL peak at 11 K and RT are in
support of the improvement of the structural properties. The
observations of PL peak blueshift with increasing excitation
show us that the strain-compensated GaAsSb/GaAs QWs
possess many characteristics of type-I QWs.

may be ascribed to the decrease in the strain accumulation
and higher structure quality of strain-compensated QWs.7
That is, the contribution of strain compensation to the overall
structure is that it does not allow a significant amount of
overall strain to accumulate as the layer is grown. Meanwhile, improvement in the PL emission strength is observed
for the insertion of GaAsP layer. Higher peak intensity from
B344 than from B325 at 11 K indicates that additional electron confinement enhances the oscillator strength of the QW
transition. The lower RT emission intensity was also observed for B325, indicating that the dislocations that act as
This work was partially supported by the National Natunonradiative recombination centers have possibly been introral Science Foundation of China through Grant No.
duced into B325 due to the partial relaxation. A very mean60276003 and by the National Science Foundation of the
ingful fact is that the PL peak energy shifts to 1.041 eV for
USA 共No. 0070125兲. The authors are grateful for Professor
B344 from 1.051 eV for B325, possibly owing to the Sb
Junming Zhou’s help with the XRD experiment.
content increase from 0.36 to 0.39.
Actually, the PL peak position of B325 exhibits a much
stronger blueshift as compared to that of B344 when the
excitation intensity increases, as shown in Fig. 5. A larger
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