Compositional dependence of the bowing parameter for highly strained InGaAs/GaAs
quantum wells
T. K. Sharma,
1,
* R. Jangir,
1
S. Porwal,
1
R. Kumar,
1
Tapas Ganguli,
1
M. Zorn,
2,†
U. Zeimer,
2
F. Bugge,
2
M. Weyers,
2
and S. M. Oak
1
1
Semiconductor Laser Section, Raja Ramanna Centre for Advanced Technology, Indore 452 013, Madhya Pradesh, India
2
Ferdinand-Braun-Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12489 Berlin, Germany
Received 4 May 2009; published 6 October 2009
Highly strained InGaAs/GaAs quantum wells QWs are studied using the complementary spectroscopic and
high-resolution x-ray diffraction HRXRD techniques. It is found that the QW features can be precisely
identified by solving the Schrödinger equation for a rectangular shape QW, thus ignoring any indium segre-
gation effect and considering only the compositional dependence of bowing parameter C while using the QW
parameters obtained from HRXRD measurements. The compositional dependence of “C” for In
x
Ga
1-x
As QWs
0.294 x 0.42 can be given by a linear relationship of C = 0.3525+ 0.9028x, which provides a conduction
band offset E
c
of the functional form: E
c
= 0.7529x + 0.2917x
2
- 0.4785x
3
using the band offset Q
c
value
of 0.53. It is also observed that Q
c
is independent of the composition of QWs. Though the QW sample with the
maximum strain showed some relaxation R 3.4% as measured by the reciprocal space mapping in HRXRD,
still it is largely insignificant and does not affect the measured value of “C” for the present set of QW samples.
DOI: 10.1103/PhysRevB.80.165403 PACS numbers: 78.66.Fd, 68.65.Fg
I. INTRODUCTION
Highly strained In
x
Ga
1-x
As / GaAs quantum wells QWs
are widely used for the development of laser diodes operat-
ing beyond 1.2 m, which are a key components in the local
area network LAN and metropolitan area network MAN
links especially for the fiber-to-the-home applications.
1–4
Re-
cently, such lasers with significantly improved device char-
acteristics have been reported by several groups.
5–9
For
MAN and LAN links, it is necessary to develop a QW laser
operating at wavelengths longer than 1.2 m.
3,10
For the
long wavelength operation of InGaAs QW lasers, it is nec-
essary that a sufficient amount of indium is incorporated into
the QW. However, strain puts an upper limit on the indium
content for a pseudomorphic InGaAs QW.
10,11
Earlier, we
reported the metal organic vapor phase epitaxy MOVPE
growth of highly strained InGaAs QWs with indium content
exceeding 40% by using only the conventional sources.
10
Spectroscopic techniques play a vital role in the development
of advanced semiconductor devices and in fact have been
applied extensively to study strained InGaAs/GaAs QWs
where an accurate knowledge of all QW transitions, as well
as the barrier band gap energy is routinely obtained.
10–15
Modulation spectroscopic techniques in general have been
extremely useful for studying moderately strained x 0.2
In
x
Ga
1-x
As / GaAs QW structures.
15–17
Complementary spec-
troscopic techniques such as photoluminescence PL, pho-
toreflectance PR, and surface photovoltage spectroscopy
SPS, where in the PR and SPS technique one essentially
measures the absorption spectrum of semiconductors are of-
ten applied to study such quantum structures.
11–18
Recently,
we applied PL and SPS techniques to investigate InGaAs/
GaAs QWs where it was demonstrated that SPS provides
more information about QWs than the routinely used PL
technique even at room temperature.
12
We were able to
identify the QW transitions by numerically solving the
Schrödinger equation using an envelope function approxima-
tion for a finite square potential well only for the lowest
values of indium content x 0.2. We were unable to do a
similar exercise for In
x
Ga
1-x
As x 0.30 QWs with large
built-in strain where it was observed that even the ground
state GS transition could not be matched accurately by us-
ing the QW parameters determined from high-resolution
x-ray diffraction HRXRD measurements. Long back, a
similar observation has been made by Muraki et al.
19
where
they observed that one needs to choose a particular value of
the band offset in order to match the GS energy measured by
the PL experiments with the numerically calculated transi-
tions energy. It was further observed by them that for a few
InGaAs/GaAs QW samples which were grown at a higher
temperature, an inclusion of the indium segregation effect
was absolutely essential in order to get a genuine match be-
tween experiment and theory which was otherwise impos-
sible simply by choosing an arbitrary value of the band
offset.
In this paper, we present our results related to the spec-
troscopic investigation of highly strained InGaAs QWs
where we obtained a reasonable match between experiment
and theory with a perfect rectangular shape QW without any
indium segregation. Unlike a constant value reported in the
literature,
20
we found that the bowing parameter for
In
x
Ga
1-x
As QWs 0.294 x 0.42 is rather compositional
dependent. Our analysis is further supported by HRXRD
measurements where we did not find any signature of indium
segregation.
II. EXPERIMENTAL DETAILS
Highly strained In
x
Ga
1-x
As / GaAs QW samples were
grown in a horizontal low-pressure MOVPE reactor AIX
200/4 reactor with a rotating substrate holder on GaAs 001
substrates. Arsine AsH
3
and the trimethyl compounds of
gallium TMGa and indium TMIn were used as precur-
sors. The indium content of QWs x was varied by changing
PHYSICAL REVIEW B 80, 165403 2009
1098-0121/2009/8016/16540311 ©2009 The American Physical Society 165403-1