Shiro Tsukamoto

Fabrication of GaAs quantum wires on epitaxially grown V grooves by metal‐organic chemical‐vapor deposition

Successful fabrication of thin GaAs quantum wires (120–200 A)×(200–300 A) by a novel metal‐organic chemical‐vapor‐deposition growth technique is reported. The GaAs quantum wires were grown on a V groove formed by two GaAs triangular prisms which were selectively grown on SiO2 masked substrates. The V groove has a very sharp corner at the bottom, which results in reduction of the effective width of the quantum wire structures. The measurement of photoluminescence and photoluminescence excitation spectra with polarization dependence indicate the existence of the quantized state in the quantum wires.

Fabrication of GaAs quantum wires (∼10 nm) by metalorganic chemical vapor selective deposition growth

GaAs triangular‐shaped quantum wires with the lateral width of ∼10 nm are fabricated by metalorganic chemical vapor selective deposition growth technique. The lateral dimension is determined by both photoluminescence (PL) measurement and a high‐resolution scanning electron micrograph observation. A systematic change in the size of the quantum wire exhibits consistent blue shifts of the PL peak keeping high intensities, which demonstrates enhanced two‐dimensional quantum confinement with the material of high quality.

Fabrication of GaAs arrowhead-shaped quantum wires by metalorganic chemical vapor deposition selective growth

We fabricated GaAs arrowhead‐shaped quantum wires utilizing both the selective growth technique and the difference in the stabilized crystal facet between GaAs and Al0.4Ga0.6As; the stabilized facet of the GaAs layer is (111)A and that of the Al0.4Ga0.6As layer is (311)A. A systematic change in the size of the quantum wire exhibits blue shifts of the photoluminescence peak, which is due to enhancement of the two‐dimensional quantum confinement effect.

GAAS QUANTUM DOTS WITH LATERAL DIMENSION OF 25 NM FABRICATED BY SELECTIVE METALORGANIC CHEMICAL VAPOR DEPOSITION GROWTH

We report on in situ fabrication and the photoluminescence spectra of pyramid‐shaped GaAs dot structures grown on (100) GaAs substrates using selective epitaxial growth by metalorganic chemical vapor deposition. The dot structures have lateral size of 25 nm and the period of 140 nm, showing a clear photoluminescence peak with strong intensity. In addition, energy change of magnetophotoluminescence spectra demonstrates the enhancement of exciton binding energy due to lateral confinement.

Molecular‐beam epitaxial growth of high‐quality InSb on InP and GaAs substrates

Epitaxial layers of InSb were grown on InP and GaAs substrates by molecular beam epitaxy. The dependence of the epilayer quality on flux ratio, J sub Sb4/J sub In, was studied. Deviation from an optimum value of J sub Sb4/J sub In (approx. 2) during growth led to deterioration in the surface morphology and the electrical and crystalline qualities of the films. Room temperature electron mobilities as high as 70,000 and 53,000 sq cm /V-s were measured in InSb layers grown on InP and GaAs substrates, respectively. Unlike the previous results, the conductivity in these films is n-type even at T = 13 K, and no degradation of the electron mobility due to the high density of dislocations was observed. The measured electron mobilities (and carrier concentrations) at 77 K in InSb layers grown on InP and GaAs substrates are 110,000 sq cm/V-s (3 x 10(15) cm(-3)) and 55,000 sq cm/V-s (4.95 x 10(15) cm(-3)), respectively, suggesting their application to electronic devices at cryogenic temperatures.

Fabrication of InGaAs quantum dots on GaAs(0 0 1) by droplet epitaxy

Abstract We have proposed a new self-organized growth method for InGaAs quantum dots (QDs) using droplet epitaxy with highly dense Ga droplets. During the crystallization process of InGaAs in droplet epitaxy, the highly dense Ga droplets effectively prevented the two-dimensional growth of InGaAs. Phase-separation during annealing for the InAs–GaAs system resulted in the formation of high-quality InGaAs QDs in the upper part of the sample with a flat surface.

New Self-Organized Growth Method for InGaAs Quantum Dots on GaAs(001) Using Droplet Epitaxy

Quantum dot (QD) systems for InGaAs/GaAs without a wetting layer have been fabricated on GaAs (001) surfaces by a new self-organized growth method using droplet epitaxy with highly dense Ga droplets. Droplets of InGa alloy with highly dense Ga droplets have been formed by supplying 1) Ga, 2) In and 3) Ga molecular beams, sequentially. These highly dense Ga droplets have successfully prevented the two-dimensional growth of InGaAs during crystallization under As flux supply. In the plan-view transmission electron microscope image, the InGaAs QDs with the density of 7×109 cm-2 are observed. These QDs show a very sharp photoluminescence peak (full width half maximum (FWHM): 21.6 meV) at 946 nm.

High density InAs∕GaAs quantum dots with enhanced photoluminescence intensity using antimony surfactant-mediated metal organic chemical vapor deposition

The antimony surfactant-mediated growth of InAs∕GaAs quantum dots (QDs) by metal organic chemical vapor deposition was investigated. The authors show that the growth of InAs QDs on Sb:GaAs(100) can result in both a strong increase of the dot density, up to 1011cm−2, and the suppression of coalescence. They achieved InAs∕Sb:GaAs QDs with density above 4×1010cm−2, ground-state emission above 1.30μm, and enhanced photoluminescence intensity at room temperature compared to that of InAs∕GaAs QDs. Remarkably, InAs∕Sb:GaAs QDs do not exhibit an emission blueshift under annealing at temperatures as high as 630°C, contrary to InAs∕GaAs QDs.

Nanoscale InGaAs concave disks fabricated by heterogeneous droplet epitaxy

The detailed cross-sectional structure of InGaAs quantum dots fabricated by a heterogeneous droplet epitaxy method was investigated by means of cross-sectional transmission electron microscopy observation. It was confirmed that concave disks without any dislocations or wetting layer were formed at the upper part of the flat surface. This result was consistent with the change of photoluminescence intensity and peak position. The sizes of the disks were estimated to be 30 and 12 nm in lateral and vertical directions, respectively. From this estimation, the occurrence of a phase-separation effect is suggested.

Narrow photoluminescence linewidth (<17 meV) from highly uniform self-assembled InAs/GaAs quantum dots grown by low-pressure metalorganic chemical vapor deposition

We report highly uniform self-assembled InAs quantum dots (QDs) emitting at 1.3 μm, grown on GaAs substrates by low-pressure metalorganic chemical vapor deposition. By optimizing the InAs growth rate and capping the QDs with GaAs using triethylgallium as a gallium source, we have achieved a narrow photoluminescence (PL) inhomogeneous linewidth of 16.5 meV (at 7 K) from QDs with a density of 1.7×1010 cm−2. Furthermore, we show by temperature-dependent PL measurements that the QDs exhibit almost no dependence of linewidth on temperature due to their high uniformity.