Semiconductor Quantum Structures and Quantum Devices

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Semiconductor Quantum Structures and Quantum
Devices
????????? C.P. Lee ?????????

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?????? C.P. Lee ?????????

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?????? K.W. Sun ???????

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?????? Y.W. Suen ???????
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Publications from this project
S.D. Lin, H.C. Lee, K.W. Sun and C.P. Lee,
?Investigation of electron-optical phonon
interactions in moderate wide In0.15Ga0.85As/GaAs
strained quantum wells?, Journal of Luminescence
94-95, 761-766 (2001). B.C. Lee, S.D. Lin, C.P.
Lee, H.M. Lee, J.C. Wu, and K.W. Sun, ?Selective
growth of single quantum dots using strain
engineering?, Applied Physics Letters 80, 326-328
(2002). H.C. Lee, K.W. Sun and C.P. Lee,
?Structure effects on electron-optical phonon
interaction in GaAs/AlxGa1-xAs quantum wells?,
Journal of Applied Physics 92, 268 (2002). K.W.
Sun, J.C. Wu, B.C. Lee and C.P. Lee, ?Selective
growth and photoluminescence studies of InAs
quantum dot array on patterned GaAs (001)
substrates?, Nanotechnology 13, 576-580
(2002) S.D. Lin, H.C. Lee, K.W. Sun and C.P.
Lee, ?Investigation of hot electron-neutral
acceptor luminescence in moderate wide
In0.15Ga0.85As/GaAs multiple quantum wells?, 2001
International Conference on Dynamical Processes
in Excited States of Solids, July 1-4, 2001 Lyon,
France
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H.C. Lee, K.W. Sun and C.P. Lee, ?Dependence of
electron-optical phonon interaction on the Al
composition in GaAs/AlxGa1-xAs quantum wells?,
Tenth International Conference on Phonon
Scattering in Condensed Matter, August 12-17,
2001 Hanover, USA. H.C. Lee, C.P. Lee and K.W.
Sun, ?Dependence of electron energy loss rate on
well width and Al composition in GaAs/AlxGa1-xAs
quantum well structures?, Tenth International
Conference on Phonon Scattering in Condensed
Matter, August 12-17, 2001 Hanover, USA B.C.
Lee, H.M. Lee, J.C. Wu, Y.P. Chang, K.W. Sun, and
C.P. Lee, ?Molecular beam epitaxial growth and
photoluminescence studies of InAs self-organized
quantum dots grown on patterned GaAs (001)
substrates?, pp. 376-380, in Physics, Chemistry
and Application of Nanostructures, Reviews and
Short Notes to Nanomeeting 2001, Published by
World Scientific, ISBN 981-0204618-8 S.D. Lin,
C.P. Lee, W.H. Hsieh, and Y.W. Suen,
?Self-assembled GaAs antiwires in In0.53Ga0.47As
matrix on (100) InP substrates?, Applied Physics
Letters 81, 3007 (2002). S.D. Lin and C.P. Lee,
?Hole Schottky barrier height enhancement and its
application to metal-semiconductor-metal
photodetector?, Journal of Applied Physics 90,
5666 (2001).
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Y. W. Suen, W. H. Hsieh, L. C. Li, T. C. Wan, C.
H. Kuan, S. D. Lin, C. P. Lee, and H. H. Cheng,
Using a pulsed phase lock loop to detect
high-frequency magnetotransport
properties of two-dimensional electron systems,
Proceedings of the 15th international conference
on High Magnetic Fields in Semiconductor
Physics, 5 - 9 August 2002, Clarendon Laboratory,
Oxford, UK H.C. Lee, K.W. Sun and C.P. Lee,
Investigation of reduced dimensionality on hot
carrier relaxation in highly excited GaAs ,
submitted to Physical Review B (November,
2002). K.W. Sun, C.L. Huang, G.B. Huang and H.C.
Lee, ?Inter- and intra-subband relaxation of hot
electrons in GaAs/AlGaAs Quantum wells?,
submitted to Journal of Physics Condensed Matter
(October, 2002).
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Summary of major results

1. Growth and characterization of of InAs quantum
   dots
2. Growth and characterization of quantum rings
3. Growth and characterization of Quantum wires
4. Quantum dot infrared detectors
5. Electron-LO phonon interactions in quantum
   structures
6. Inter- and inter-subband scattering in quantum
   wells
7. High-frequency magnetotransport properties of
   2DES

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Growth and characterization of of InAs quantum
dots
In this portion of the project, we have
successfully grow InAs QDs inside InGaAs QWs
. The luminescence from the dots are pushed
toward 1.3?m by changing either the In
compositions or the well widths of the InGaAs
QWs. We also discover that the high growth
temperatures of QDs inside the wells also lead to
longer emission wavelengths.
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The emission wavelength moves toward longer
wavelengths as the increasing In composition in
QWs.
The luminescence spectra of QDs grown inside the
QWs with different well width.
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The spectra of photoexcited QDs at room
temperature with different excitation power.
The photoluminescence spectra of QDs grown at
different temperatures.
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Growth and characterization of quantum rings
We have demonstrated the growth of InAs quantum
ring using Stranski-Krastanov growth method. A
partial capping layer was first deposited on the
top of the InAs QDs. After a thermal annealing
process, the QDs will transform into ring
structures.
The AFM image of the InAs quantum rings.
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Growth and characterization of Quantum wires
Our laboratory used self-assembly methods to
obtain quantum wire (QWr) and anti quantum wire
structures. Moreover, we also demonstrated the
correlation and anti-correlation behavior of
stacking QWr and anri-QWr structures.
The (110) cross-section TEM picture of stacked
InAs QWrs in InAlAs matrix lattice matched to
InP.
The (110) cross-section TEM picture of stacked
InAs QWrs in InGaAs matrix lattice matched to
InP.
AFM picture of GaAs anti-QWr structure on InGaAs
matrix.
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Orientation Dependent Mobility
GaAs wires
InGaAs
InP
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Quantum dot infrared detectors
InAs/GaAs quantum dot infrared photodetectors
were fabricated. Large detection wavelength
shift (5 to 15 µm) was demonstrated by changing
40 degrees of the epitaxy temperature. The
smaller quantum dots grown at lower temperature
generate 15 µm responses. The detectivity of the
normal incident 15 µm QDIP at 77K is
3108cmHz1/2/W. It is the best result reported so
far for QDIPs in this wavelength region and
comparable to the performance of QWIPs with the
same cutoff wavelength. A three-color detector
was also demonstrated with quantum dots grown at
medium temperature. The three color detection
comes from two groups of different sizes of dots
within one QD layer. This new type of multicolor
detector shows unique temperature tuning behavior
that has never been reported before.
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The responsivity of the QDIP measured at
different temperatures and biases.
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Electron-LO phonon interactions in quantum
structures
We have found theoretically that the reduced
dimensionality from a bulk semiconductor to a
quantum well structure has a strong effect on the
hot carrier relaxation in highly excited GaAs.
Comparisons of Electron energy loss rates in bulk
and 2D QWs.
Calculated electron energy loss rate as a
function of quantum well width.
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We have calculate the effect of phonon-plasma
coupling in the electron energy loss rate in
quantum well structures.
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Inter- and inter-subband scattering in quantum
wells
We have studied the inter-subband and
intra-subband scatterings of hot electrons in
quantum wells using the hot electron-neutral
acceptor luminescence technique. We have
observed direct evidences of the emission of
confined optical phonons by hot electrons excited
slightly above the n2 subband in
GaAs/Al0.37Ga0.63As quantum wells. Scattering
rates of photoexcited electrons via inter- and
intra-subband LO phonon emission were calculated
based on the dielectric continuum model (DCM). We
found that, for wide wells with the given Al
composition in our experiments, both the
calculated and experimental results suggest that
the scatterings of the electrons are dominated by
the confined LO phonon mode.
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Calculated electron-LO phonon scattering rates as
a function of well width.
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High-frequency magnetotransport properties of 2DES
We have studied the high-frequency transport
properties of a two-dimensional electron system
(2DES) by using a type-II phase lock loop (PLL)
for pulsed RF signals. A meandering coplanar
waveguide (CPW) is patterned on the surface of a
substrate, which contains a high-mobility 2DES in
a modulation-doped GaAs/AlGaAs heterostructure,
and is part of the traveling path for the RF
signals in the PLL. The conductivities, both the
real and the imaginary parts, of the 2DES will
affect the propagation constant of the CPW, which
can be detected by a PLL. This measurement
system is extremely useful in probing quantum dot
systems for which individual contact to each dot
is difficult to make.
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Schematic of a homemade PLL system for microwave
signals up to 18 GHz.
The most important specification of our system is
that the phase resolution is about 0.001 degree
even under very low average input power
(-100dBm) and the special designed homodyne
amplitude detection scheme also allows us to
detect very small microwave adsorption.
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(a)
(b)
(a) The pattern of the meandering coplanar
waveguide. The dark part is the metal. (b) The
amplitude and the frequency deviation Df vs
magnetic field B are shown for f01.39GHz at
T0.3K. Near the IQH plateau, the amplitude curve
shows a relatively flat feature similar to the DC
conductivity, while the phase data (Df) exhibit a
very different behavior.
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(a)
(b)
(a) The amplitude and (b) the frequency deviation
Df (phase) vs magnetic fields for several RF
frequencies. Each curve is offset for clarity.
The amplitude curve shows very flat region at QH
plateau region at a lower frequency but becomes
curved at a higher frequency. The Df curves show
a very strong dependence on the frequency. The
horizontal dashed lines give a rough reference
for a lossless condition given by the center of
the IQH plateau.
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Equipments and setups
A. National Chiao Tung University
A near field optical measurement system which is
designed for the studies of micro-Ramann and
photoluminescence of quantum dots and quantum
structures is currently under construction.
B. National Dong Hwa University
We have completed the construction of a
femtosecond Tisapphire laser based luminescence
up conversion system with the proposal grant and
matching funds
C. National Chung Hsing University
We have set up a high-sensitivity PLL detection
system for pulsed signals up to 18GHz.
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a femtosecond Tisapphire laser based
luminescence up conversion system