Antimonide quantum dots enable novel photonic devices

TLDR: In this paper, the authors used nanostructured semiconductors, such as a quantum dot (QDs), to create near-IR luminescent material on GaAs and Si substrates.

Abstract: Long-wavelength (ie, near-IR) light-emitting devices, especially 13and 155μm lasers, are needed for ubiquitous fiberoptic communication networks To achieve low-cost, low-power consumption and high performance from such light sources, we would like to fabricate them on low-cost, high-quality semiconductor substrates such as gallium arsenide and silicon wafers But the crystal lattice mismatch between these substrates and narrow-energy-bandgap semiconductors makes it difficult to obtain near-IR light-emitting materials using normal fabrication techniques Recently, some approaches for creating these luminescent materials have been proposed As one method, the epitaxial growth of nitride-based semiconductors—such as GaInNAs— on GaAs substrates is being widely investigated SiGe, silicon quantum dots (QDs), and III-V semiconductors bonded directly to Si are also being studied to find a photonics technology that allows us to fabricate light-emitting materials on Si However, obtaining optimized material characteristics for highintensity and near-IR luminescence with these material fabrication techniques is also difficult To avoid these difficulties, we used nanostructured semiconductors, such as a quantum dots (QDs), to create near-IR luminescent material on GaAs and Si substrates Quantum dots have very interesting characteristics, including quantum confinement of carriers and high luminescent efficiency In addition, QD structures can be grown without requiring lattice matching between the QDs and the substrate Without this restriction, we are free to use antimonide-based III-V semiconductor materials, which have very narrow bandgaps These materials were not used in the past because of the very large lattice mismatch (more than 10%) between Sb-based materials and GaAs or Si Therefore, we created Sb-based III-V semiconductor QD structures (ie, the Sb atoms are included in Figure 1 Atomic force microscope image of Sb-based quantum dots (QDs) on a GaAs surface

Figures

Figure 3. A Sb-based QD vertical-cavity surface-emitting laser (VCSEL) structure (left) and the emission spectrum from an optically pumped VCSEL structure (right).

Figure 2. Light emission from Sb-based QD structures on GaAs in the fiber-optic communications waveband.

Figure 1. Atomic force microscope image of Sb-based quantum dots (QDs) on a GaAs surface.

Full text

SPIE Newsroom
10.1117/2.1200612.0546
Antimonide quantum dots
enable novel photonic devices
Naokatsu Yamamoto, Kouichi Akahane,
Shin-ichirou Gozu, Akio Ueta, and Masahiro Tsuchiya
Structures based on antimonide III-V semiconductor quantum dots can
provide communications lasers on inexpensive substrates.
Long-wavelength (i.e., near-IR) light-emitting devices, espe-
cially 1.3- and 1.55
µ
m lasers, are needed for ubiquitous fiber-
optic communication networks. To achieve low-cost, low-power
consumption and high performance from such light sources, we
would like to fabricate them on low-cost, high-quality semicon-
ductor substrates suc h as gallium a rsenide and silicon wafers.
But the crystal lattice mismatch between these substrates and
narrow-energy-bandgap semiconductors makes it difficult to ob-
tain near-IR light-emitting materials using normal fabrication
techniques.
Recently, some approaches for creating these luminescent
materials have been proposed. As one method, the epitaxial
growth of nitride-based semiconductors—such as GaInNAs—
on GaAs substrates is b eing widely investigated. S iGe, silicon
quantum dots (QDs),
1
and III-V semiconductors bonded di-
rectly to Si are also being studied to find a photonics technol-
ogy that allows us to fabricate light-emitting materials on Si.
However, obtaining optimized material characteristics for high-
intensity and near-IR luminescence with these material fabrica-
tion techniques is also diffic ult. To avoid these diffic u lties, we
used nanostructured semiconductors, such as a quantum dots
(QDs), to create near-IR luminescent material on GaAs and Si
substrates.
Quantum dots have very interesting characteristics,
2
includ-
ing quantum confinement of carriers and high luminescent effi-
ciency. In addition, QD structures can be grown without requir-
ing lattice matching between the QDs and the substrate. With-
out this restriction, we are free to use antimonide-based III-V
semiconductor materials, which have very narrow bandgaps.
These materials were not used in the past because of the very
large lattice mismatch (more than 10%) between Sb-based ma-
terials and GaAs or Si. Therefore, we created Sb-based III-V
semiconductor QD structures (i.e., the Sb atoms are included in
Figure 1. Atomic force microscope image of Sb-based quantum dots
(QDs) on a GaAs surface.
or neighbor the QD structure) formed on GaAs and Si to achieve
near-IR emission.
We grew the Sb-based QD structure using molecular beam
epitaxy (MBE). First, we proposed a Si-atom irradiation tech-
nique and optimized the growth conditions to improve the den-
sity of the QDs (a density as high as 10
10
/cm
2
is nec essary to de-
velop a laser or other light-emitting device).
3, 4
We b elieved that
emission could be obtained by a confined-carrier recombination
in this nanostructured Sb-based semiconductor. Figure 1 shows
the Sb-based QD structure formed on a GaAs surface under op-
timized growth conditions. The height a nd diameter of the QD
structures are
∼ 7.5 and 25nm, respectively. We also obtained a
density as high as 2
× 10
10
QD/cm
2
.
Continued on next page

10.1117/2.1200612.0546 Page 2/3
SPIE Newsroom
Figure 2. Light emission from Sb-based QD structures on GaAs in the
fiber-optic communications waveband.
Figure 3. A Sb-based QD vertical-cavity surface-emitting laser (VC-
SEL) structure (left) and the e mission spectrum from an optically
pumped VCSEL structure (right).
We observed emission at wavelengths as long as 1.3- and
1.55
µ
m,asshowninFigure2,fromtheSb-basedQDstructure
embedded in GaAs. We also obtained these wavelengths from
an LED that contained QDs in the active regions. We tried to de-
velop a vertical-cavity surface-emitting laser (VCSEL) c ontain-
ing Sb-based QDs because near-IR VCSELs are expected to be
one of the candidates for the light source used in 10Gb Ether-
net (or faster) optical networks. In addition, a high-performance
distributed Bragg reflector (DBR) necessary to form the optical
cavity in VCSELs is simple to form in the AlGaAs system.
Figure 4. Sb-based III-V semiconductor QD structure on silicon.
We fabricated, respectively, current-injected and optically
pumped Sb-QD VCS ELs. Figu re 3 presents a cross-section of our
current-injection Sb-based QD VCSEL and the 1.55
µ
memission
spectrum from the optically pumped VCSEL. The Sb-based QD
active layers and AlGaAs DBR mirrors can be grown monolith-
ically using epitaxial growth on a G aAs substrate. This is a sim-
plewaytomaketheseVCSELs.Wefoundthata1.52
µ
memis-
sion peak can be obtained at room temperature with continuous
current injection.
4
A sharp 1.55
µ
memissionpeakandthresh-
old characteristics of the curve of the optical pump power ver-
sus laser power were also observed from the optica lly pumped
VCSELs. These results may indicate a possibility of laser opera-
tion in the 1.5
µ
m waveband u sing the Sb-QD-VCSEL structure.
However, we are continuing characterization and optimization
of Sb-based QD materials and laser structures to clarify the las-
ing operation and develop the VCSEL for practical use.
Recently, we also focused on Sb-based QDs fabricated on a Si
wafer for Si photonics technology (see Figure 4). We found that a
high-density (more than 10
10
/cm
2
)ofsmall(8nm)Sb-basedQDs
can be grown on Si using MBE.
5
We expect that this will enable
us to achieve energy-bandgap engineering, high carrier mobil-
ity, and near-IR light emission for novel photonic devices on Si
wafers.
Previous techniques considered for forming light emitters at
these wavelengths from semiconductor materials on GaAs and
Si wafers were very difficult. To solve this problem, we proposed
fabricating Sb-based QDs on these wafers, which emit in the
low-loss window of optical fiber. We also succ essfully demon-
strated 1.5
µ
m emissions from a Sb-based QD VCSEL. Addition-
ally, we fabricated a Sb-based QD structure on a Si wafer, which
may b ecome a novel material for making Si-light emitters and
optoelectronics devices. We believe that Sb-based QDs on low-
cost and high-performance GaAs and Si wafers will enable u s
to achieve breakthroughs in fabricating novel photonics devices
for ubiquitous communication networks.
Continued on next page

10.1117/2.1200612.0546 Page 3/3
SPIE Newsroom
We thank H. Sotobayashi, T. Kawanishi, M. Izutsu, T. Itabe, and F.
Tomita at NICT for encouragement throughout this work. We also
thank Y. Mitsumori of Tohoku University, N. Ohtani of Doshisha Uni-
versity, and all of the staff at the Photonics Device Laboratory (PDL)
of NICT for technical assistance and a dvice.
Author Information
Naokatsu Yamamoto, Kouichi Akahane,
Shin-ichirou Gozu, Akio Ueta, and Masahiro Tsuchiya
Advanced Communications Technology Group
National Institute of Information and Communications
Technology
Tokyo, Japan
http://act.nict.go.jp/lwd/staf f/naokatsu/
http://act.nict.go.jp
Naokatsu Yamamoto is a researcher in the Advanced Commu-
nications Technology Group at NICT. His research interests in-
clude development and creation of novel photonic devices with
attractive material characteristics and nanostructures.
References
1. N. Yamamoto, A. Sumiya, and H. Takai, Electroluminescence from photo-chemically
etched silicon, Mater. Sci. Eng. B69-70, pp. 205–209,2000.
2. Y. Arakawa and H. Sakaki, Multidimensional quantum well laser and temperature
dependence of its threshold current, Appl. Phys. Lett. 40, pp. 939–941, 1982.
3. N.Yamamoto,K.Akahane,S.Gozu,andN.Ohtani,Over 1.3
µ
m continuous-wave
laser emission from InGaSb quantum-dot laser diode fabricated on GaAs substrates, Appl.
Phys. Lett. 86, p. 203118, 2005.
4. N. Yamam o to, K. Akahane, S. Gozu, A. Ueta, and N. Ohtani, 1.55-
µ
m-waveband
emissions from Sb-based quantum-dot vertical-cavity surface-emitting laser structures fab-
ricated on GaAs substrate, Jpn. J. Appl. Phys 45, pp. 3423–3426,2006.
5. N. Yamamoto, K. Akahanea, S. Gozu, A. Ueta, N. Ohtani, and M . Tsuchiya, Sb-
based quantum dots for creating novel light-emitting devices for optical communications,
Proc. SPIE 6393 , 2006. Also Growth of InGaSb quantum dot structures on GaAs and
silicon substrates, Jpn. J. Appl. Phys., submitted.
c
 2006 SPIE—The International Society for Optical Engineering

Frequently asked questions

Q1. What contributions have the authors mentioned in the paper "Antimonide quantum dots enable novel photonic devices" ?

To achieve low-cost, low-power consumption and high performance from such light sources, the authors would like to fabricate them on low-cost, high-quality semiconductor substrates such as gallium arsenide and silicon wafers. SiGe, silicon quantum dots ( QDs ), and III-V semiconductors bonded directly to Si are also being studied to find a photonics technology that allows us to fabricate light-emitting materials on Si. To avoid these difficulties, the authors used nanostructured semiconductors, such as a quantum dots ( QDs ), to create near-IR luminescent material on GaAs and Si substrates. Without this restriction, the authors are free to use antimonide-based III-V semiconductor materials, which have very narrow bandgaps. Therefore, the authors created Sb-based III-V semiconductor QD structures ( i. e., the Sb atoms are included in Figure 1.