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ABSTRACT: Self-assembled GaAs anti quantum dots (AQDs) were grown in an InAs matrix via migration enhanced molecular beam epitaxy. The transmission electron microscopy image showed that the 2D to 3D transition thickness is below 1.5 monolayers (MLs) of GaAs coverage. The average diameter and height of the GaAs AQDs for 1.5 ML GaAs coverage taken from the atomic force microscopy image were approximately 29.0 nm and 1.4 nm, respectively. The density was approximately 6.0 x 10(10) cm(-2). The size of the AQDs was enlarged in the InAs matrix compared with that on the surface. These results indicate that the GaAs AQDs in the InAs matrix under tensile strain can be effectively formed with the assistance of the migration enhanced epitaxy method.
Journal of Nanoscience and Nanotechnology 02/2012; 12(2):1480-2. · 1.56 Impact Factor
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Pilkyung Moon,
S.-K. Ha,
J. D. Song,
J. Y. Lim,
S. Bounouar,
F. Donatini,
L. S. Dang,
J. P. Poizat,
J. S. Kim,
W. J. Choi,
I. K. Han, J. I. Lee
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ABSTRACT: We fabricated low‐density GaAs∕AlGaAs quantum dots for single photon source by droplet epitaxy. We investigated the emission energies of the dots and underlying superlattice by using photoluminescence and cathodoluminescence measurements. By forming a mesa etched structure, we distinguished the transitions from the superlattice and the dots. And we calculated the diffusion length in this system from the peak shift of the superlattice, and applied the diffusion to the dots to investigate the emission energy shift of the QDs.
AIP Conference Prooceedings; 07/2011
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ABSTRACT: We have investigated the influence of alloy buffer and capping layers on the shape, size, and density of self-assembled InAs/GaAs quantum dots. Cross-sectional scanning tunneling microscopy (XSTM) images reveal ellipse-shaped dots with highest (lowest) diameter, height, and density, for dots with (without) surrounding alloy layers. Furthermore, the wetting layer is thicker in the presence of the alloy layers. We propose a strain-based mechanism for dot formation and collapse in the absence and presence of alloy buffer and capping layers. This mechanism is likely to be applicable to a wide range of lattice-mismatched thin-film systems.
Applied Physics Letters 10/2009; 95(16):163114-163114-3. · 3.84 Impact Factor
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ABSTRACT: We have investigated the origins of electronic states in individual (uncoupled) quantum dots (QDs) and the surrounding wetting layers (WLs) using a combination of cross-sectional scanning tunneling microscopy (XSTM) and scanning tunneling spectroscopy (STS). XSTM images reveal uncoupled ellipse-shaped QDs with 18±5 nm (9±3 nm ) major (minor) axes. Room temperature STS spectra reveal a gradient in the effective bandgap within the QDs with smallest values near the QD core and top surfaces. The variations in effective bandgap are apparently dominated by indium composition gradients, with minimal effects due to the QD shape and strain. Indium composition gradients also dominate the effective bandgap variations in the WL.
Journal of Applied Physics 08/2009; · 2.17 Impact Factor
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ABSTRACT: The effect of rapid thermal annealing temperature on the trap properties of Au/n-GaAs Schottky diodes with embedded InAs quantum dots in asymmetric In0.2Ga0.8As wells have been investigated by capacitance–voltage (C –V) and low frequency noise (LFN) measurements in both reverse and forward bias regimes. The current noise spectra show 1/f behaviour and generation–recombination (g–r) noise, attributed to uniformly distributed traps in energy and to a discrete trap level in the energy band-gap of the GaAs capping layer, respectively. The experimental results show that the annealing temperature is closely related with the level of these noise sources. The apparent doping concentrations, calculated from the C –V characteristics, indicate that the density of trapping states near the buffer layer interface is increased as the annealing temperature increases. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
physica status solidi (b) 01/2009; 246(4):880 - 884. · 1.32 Impact Factor
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ABSTRACT: The trap properties of Au/n-GaAs Schottky diodes with embedded InAs quantum dots (QDs) and different ideality factors were studied by capacitance-voltage (C-V) and low-frequency noise (LFN) measurements in the reverse bias regime. The reverse current noise spectra show 1/f behaviour and g-r noise, attributed to uniformly distributed traps in energy or to a discrete trap level in the energy band-gap of the GaAs capping layer, respectively. The Schottky contact performance or characteristics is closely related with the level of these noise sources. The C-V characteristics indicate the existence of traps with Gaussian energy distribution in the GaAs capping layer and in the InAs QDs layer. From analysis of the C-V characteristics, the density and the activation energy of these trap distributions are determined. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
physica status solidi (c) 09/2008; 5(12):3617 - 3621.
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ABSTRACT: We have compared the performances of 980-nm InGaAs quantum-dot and quantum-well laser diode grown by molecular beam epitaxy. The quantum-dot laser diodes show superior performance to the quantum-well laser diodes in their lower threshold current density and temperature sensitivity.
Lasers and Electro-Optics - Pacific Rim, 2007. CLEO/Pacific Rim 2007. Conference on; 09/2007
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ABSTRACT: Schottky contacts on n-type GaAs with embedded InAs quantum dots (QDs) were studied by current–voltage (I–V) and low-frequency noise measurements. For comparison, diodes not containing QDs were investigated as reference devices. A wide distribution of the ideality factor was observed, correlated with the level of the leakage current. Reverse I–V characteristics on the logarithmic scale indicate that the space-charge limited current dominates the carrier transport in these diodes. In all diodes, the reverse current noise spectra show 1/f behaviour, attributed to traps uniformly distributed in energy within the band-gap of the GaAs capping layer. Depth profiling measurements of the 1/f noise power spectral density demonstrate the impact of the QDs on these traps. In diodes containing QDs, in addition to the 1/f noise, a generation–recombination noise is found originating from a deep trap level localized in the vicinity of the QD plane.
Semiconductor Science and Technology 08/2007; 22(10):1086. · 1.72 Impact Factor
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ABSTRACT: In this article, we present an in-depth study of the effects of the structural and optical properties of InAs “dots in an In0.2Ga0.8As well” (DWELL) and InAs “dots in an asymmetric In0.2Ga0.8As well” (asym. DWELL) grown by migration-enhanced molecular beam epitaxy. The energy spacing (ΔE1) between the ground-state and the first-excited-state transitions increases from 66 meV for the DWELL to 73 meV for the asym. DWELL. These results are consistent with ΔE1 measured by photoluminescence excitation and the values of activation energy fitting. The photoluminescence linewidth of the asym. DWELL (40 meV) is narrower than that of the DWELL (70 meV), which shows superior uniformity in the former over the latter. The trends of the properties of the DWELL and the asym. DWELL deduced from the structural properties are in good agreement with those from the optical properties. From the results, it is strongly supported that the asym. DWELL is more suitable for application to long wavelength optical communication than the DWELL counterpart.
Journal of Applied Physics 07/2007; 102(2):023105-023105-5. · 2.17 Impact Factor
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ABSTRACT: A superluminescent diode (SLD) using J-shaped ridge waveguide and chirped multiple InAs quantum dots (QDs) with three different energy bandgap wavelengths, which are controlled by QD size, is demonstrated. The fabricated QD SLDs exhibit high continuous wave output power of 32 mW and wide spectral bandwidth up to 98 nm, covering the range 1084-1182 nm.
Electronics Letters 02/2007; · 0.96 Impact Factor
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ABSTRACT: We have investigated the carrier capture behavior of n-type modulation-doped InAs/GaAs QDs using THz time-domain spectroscopy (THz TDS) in order to estimate the total number of electrons captured by the QDs. The THz transmission of the sample with QDs (#1) is larger than that of the sample without QDs (#2). From the THz waveforms and subsequent analysis, the #1 sample shows lower conductivity which is resulted from the smaller number of free carriers due to the capture by the QDs.
Infrared Millimeter Waves and 14th International Conference on Teraherz Electronics, 2006. IRMMW-THz 2006. Joint 31st International Conference on; 10/2006
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Journal of Materials Science 07/2006; 41(15):5036-5039. · 2.02 Impact Factor
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ABSTRACT: We have investigated the half-metallicity and magnetism at the surface and interface of CrS(001) on GaAs using the full-potential linearized augmented plane-wave method within the generalized gradient approximation. Two different terminations, Cr-terminated and S-terminated surfaces, have been considered. We found, from the calculated local density of states, that both of the Cr-terminated and the S-terminated surfaces retain the half-metallicity, but the band gap for the S surface is much reduced compared to that of bulk. The magnetic moment of the Cr-terminated surface (4.08μ<sub>B</sub>) is enhanced much compared to the value of bulk (3.61μ<sub>B</sub>) while that of the interface Cr (3.29μ<sub>B</sub>) is smaller than the bulk value.
Journal of Applied Physics 05/2006; · 2.17 Impact Factor
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ABSTRACT: We strongly support Guryanov’s speculation—that a thinner wetting layer is expected with quantum dots (QDs) grown by migration-enhanced epitaxy—with structural and optical measurements. InAs QDs grown by migration-enhanced molecular-beam epitaxy showed a larger size, lower density, ∼ 40% enhanced uniformity, ∼ 2 times larger aspect ratio, and a measurement temperature insensitivity of the photoluminescence linewidth compared to QDs grown by conventional molecular-beam epitaxy. The thickness of the wetting layer for the migration-enhanced epitaxial InAs QD (2.1 nm) was thinner than that of the counterpart (4.0 nm).
Applied Physics Letters 03/2006; 88(13):133104-133104-3. · 3.84 Impact Factor
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physica status solidi (a) 02/2006; 131(1):K77 - K80. · 1.21 Impact Factor
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ABSTRACT: Magnetic properties of magnetic transition metals doped in the infinite Si nanotubes (SiNTs) with hexagonal prism structure (Si<sub>12</sub>M<sub>n</sub>, M=Fe, Co, Ni, n=1, 2) have been investigated for two different numbers of dopants per hexagonal prism by using the localized basis calculational method. The decrease (increase) of spin-down (spin-up) electrons for the n=2 case results in the increase of magnetic moments compared with the n=1 case. The calculated magnetic moment per dopant Fe atom (2.39 μ<sub>B</sub>) is larger than both of the bulk value (2.22 μ<sub>B</sub>) and previous result for finite nanotube (1.7 μ<sub>B</sub>). For Co and Ni atoms doped in the tube, the magnetic moments are smaller than those of bulk metals. The Si-Si bond lengths for the hexagonal prisms decrease compared with that of the nanotube without transition metals, but there is no dependency on different dopants. The distances between the transition metals and Si atoms decrease as the atomic number of transition metals increases, which is the same trend for the atomic radii of transition metal atoms. The doping of transition metal atoms leads to the increase of the binding energy (BE).
IEEE Transactions on Magnetics 11/2005; · 1.36 Impact Factor
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ABSTRACT: We have investigated the optical properties of InAs self-assembled quantum dots (SAQDs) with the Si-doped GaAs barrier layer. Two types of samples are fabricated according to the position of the Si-doped GaAs layer. For type A samples the Si-doped GaAs layer is grown below the QDs, whereas for type B samples the Si-doped GaAs layer is grown above the QDs. For both types of samples the excited-state emissions caused by state filling are observed in photoluminescence (PL) spectra at high excitation power densities. The bandgap renormalization of QDs can be found from the shift of the PL peak energy. Particularly, for type A samples the Si atoms act as nucleation centers during the growth of InAs QDs on the Si-doped GaAs layer and affect the density and the size of the QDs. The Si-doped GaAs layer in type A samples has more effects on the properties of QDs, such as state filling and bandgap renormalization than those of type B samples. r 2004 Elsevier B.V. All rights reserved.
01/2005; 6720(72).
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ABSTRACT: We compared the structural and optical properties of InAs∕GaAs quantum dots grown by migration enhanced epitaxy, with and without arsenic, during indium deposition. The uniformity and size of the quantum dots are enhanced in a sample without arsenic. As a result, narrower and longer wavelength photoluminescence is observed in this sample. Furthermore, the thickness of the wetting layers is reduced by ∼20% in the sample without arsenic, and this result agrees well with the speculation that metallic indium has a smaller driving force for corrugating the InAs wetting layers before they are transformed from two-dimensional to three-dimensional layers. Additionally, the photoluminescence linewidth of the sample without arsenic is insensitive to the cryostat temperature due to two major factors: the reduced thickness of the wetting layers and the enhanced uniformity. In the sample with arsenic, however, the photoluminescence linewidth shows typical anomalies.
Journal of Applied Physics 10/2004; 96(8):4122-4125. · 2.17 Impact Factor
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Microprocesses and Nanotechnology Conference, 2004. Digest of Papers. 2004 International; 02/2004
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Microprocesses and Nanotechnology Conference, 2004. Digest of Papers. 2004 International; 02/2004
