COL 11(8), 082501(2013) CHINESE OPTICS LETTERS August 10, 2013
Optical properties of excitons in strained Ga
x
In
1−x
As/GaAs quantum dot: effect of geometrical confinement
on exciton g-factor
N. R. Senthil Kumar
1
, A. John Peter
2∗
, and Chang Woo Lee
3
1
Department of Physics, RVS School of Engineering College, Dindigul-624 401, India
2
Department of Physics, Govt. Arts College, Melur-625 106, Madurai, India
3
Department of Chemical Engineering and Green Energy Center, College of Engineering,
Kyung Hee University, 1Seochun, Gihung, Yongin, Gyeonggi 446-701, Korea
∗
Corresponding author: a.john.peter@gmail.com
Received December 7, 2012; accepted Jun 28, 2013; posted online August 2, 2013
Taking into account anisotropy, nonparabolicity of the conduction band, and geometrical confinement, we
discuss t he heavy-hole excitonic states in a strained Ga
x
In
1−x
As/GaAs quantum dot for various Ga alloy
contents. The strained qu antum dot is considered as a spherical InAs dot surrounded by a GaAs barrier
material. The dependence of the effective excitonic g-factor as a function of dot radius and Ga ion content
is numerically measured. Interband optical energy with and without the parabolic effect is computed using
structural confinement. The interband matrix element for different Ga concentrations is also calculated.
The oscillator strength of interband transitions on the dot radius is studied at different Ga concentrations in
the Ga
x
In
1−x
As/GaAs quantum dot. Heavy-hole excitonic absorption spectra are recorded for various Ga
alloy contents in the Ga
x
In
1−x
As/GaAs quantum dot. Results show that oscillator strength diminishes
when dot size decreases because of the dominance of the quantum size effect. Furthermore, exchange
enhancement and exchange splitting increase as exciton confinement increases.
OCIS codes: 250.0250, 250.5590, 160.0160, 160.4760.
doi: 10.3788/COL201311.082501.
Technological progress in the techniques for g rowing low-
dimensional semiconductor crystals ha s enabled the cus-
tomization of semiconductor structures toward desired
dimensions for specific applications. These techniques
include molecular beam epitaxy, metal organic chemi-
cal vapor deposition, and electron lithography, which en-
able the confinement of carriers in one, two, or three
dimensions (1D, 2D, or 3D). Because of the reduction in
dimensionality of carrier motion, low-dimensional semi-
conductor systems exhibit unusual properties that can
be easily accessible to experimental studies and that lend
themselves to theoretical interpretation. Quantum dots,
referred to as artificia l atoms, are characterized by elec-
tron sta tes tha t take the form of discrete e nergy levels.
The majority of research has thus far focused on the
electronic and optical properties of strained heterostruc-
tures under a strain percentage of around 1%. Con-
versely, studies on experimental data for InAs/GaAs
heterostructures that exhibit a lattice mismatch of ap-
proximately 7% are scarce. Extensively investigating
these highly strained materials is of great interest be-
cause of the large splitting between the hh and lh lower
bands; such splitting considerably modifies valence band
structure. Despite the promising prospects prese nted
by these materials, however, their wide usage is con-
strained by the limited composition of barrier materi-
als. This composition is re sponsible for the tunabil-
ity of the optical band gap of highly strained mate-
rials. Doped InAs semiconducting materials present
tremendous advantages in spintronic applications be-
cause of their large g-factor, high-mobility charge car ri-
ers, and large spin-orbit interaction
[1−3]
. The electronic,
optical, and magnetic properties of the active regions
used for high-performance long-wavelength lasers based
on InGaAs semiconducting materials are interesting be -
cause low-dimensional InGa As s e miconductors are used
on GaAs substrates to develop lasers that range from 1
200 to 1 500 nm. Low-dimensional InGaAs semico nduc-
tors are ideal materials given their tre mendo us tempera-
ture stability, high performance, br oad high-modulation
bandwidths, a nd low-threshold long wavelengths
[4−12]
.
Moreover, such materia ls are the preferred light source
for wideband optical communications, especially lo ng-
term telecommunications applications
[4−12]
. Zhang et
al.
[13]
recently studied the high pulse r e petition rates
(greater than 10 GHz) of diode-pumped solid-state lasers,
which were mode locked using semiconductor saturable
absorber mirror s in 1.55- µm InAs/Ga As quantum dots.
These quantum dots are ex tensively applied in laser
diodes, optical communications, o ptica l amplifier s, and
nonlinear and photonic devices.
Preisler et al.
[14]
conducted photoluminescence exci-
tation spectroscopy under a strong magnetic field to
investigate the interband transitions in se veral ensem-
bles of self-assembled InAs/GaAs qua ntum dots. The
authors determined the excitonic polaron energies and
oscillator strengths of interband transitions. Snelling
et al.
[15]
studied the Zeeman splitting of the heavy-
hole excitons confined in GaAs quantum wells, and
other scholars interpreted heavy-hole magneto excitons
through the electron-hole exchange interaction induced
by confinement
[16]
. By co ntrast, the enhancement of
the electron-hole exchange interaction induced by 2D
confinement is rarely investigated
[17]
.
1671-7694/2013/082501(7) 082501-1
c
2013 Chinese Optics Letters
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