Y. Nagamune

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.

Formation of GaAs ridge quantum wire structures by molecular beam epitaxy on patterned substrates

A ridge quantum wire structure has been successfully fabricated on a patterned (001) GaAs substrate by first growing a (111)B facet structure with a very sharp ridge and then depositing a thin GaAs quantum well on its top. Electron microscope study has shown that a GaAs wire with the effective lateral width of 17–18 nm is formed at the ridge top. Photoluminescence and cathodoluminescence measurements indicate that one of the luminescence lines comes from the wire region at the ridge and its blue shift (∼60 meV) agrees with the quantum confined energy calculated for the observed wire structure.

Surface diffusion processes in molecular beam epitaxial growth of GaAs and AlAs as studied on GaAs (001)‐(111)B facet structures

Mechanisms of molecular beam epitaxy have been investigated for GaAs and AlAs by growing and analyzing the shapes of facet structures consisting of an (001) top surface and two (111)B side surfaces. It is found that all of the Ga flux on the three facet planes is incorporated into the film, but the growth rates on (111)B and (001) depend strongly on the As flux and are mainly determined by the diffusion of Ga ad‐atoms between the two planes. In contrast, the diffusion of Al is found to be almost negligible, irrespective of the As flux. By analyzing the shape of the facet, the diffusion length, λ, of Ga on a (001) surface is estimated to be about 1 μm at 580 °C, while that of Al is about 0.02 μm. On (111)B, λ of Ga is found to be several μms. The reflectivity of diffusing Ga atoms is found to be far less than 1 for the (001)‐(111)B boundary, and almost unity at facet boundaries where the (111)B side surfaces are bound by the (110) side walls.

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.

Single electron transport and current quantization in a novel quantum dot structure

We report on single electron transport via a novel quantum dot structure fabricated by a combination of mesa etching and gate formation. In this device electrons are confined in an etched submicron wire and squeezed further by two barrier gates. The resulting dot is of a very small size, and the number of confined electrons can be tuned down to the few electron limit. This novel structure has a large charging energy and an improved current quantization during turnstile operation. In small dots, containing only a few electrons, we found Coulomb oscillations with an unexplained multiple peak structure.

Growth process and mechanism of nanometer-scale GaAs dot-structures using MOCVD selective growth

Abstract Nanometer-scale GaAs dot-structures were fabricated by the selective epitaxial growth on SiO 2 -masked GaAs (100) substrates with low pressure metalorganic chemical vapor deposition. The growth process and the mechanism were investigated using the growth rate distribution and a surface potential model. It was revealed that the growth rates of the crystal planes change in dependence on the existence of other planes with faster growth rates, and that the in-plane migration is an important factor in the growth process. Based on these characteristics and the study on AlGaAs dot-structure growth, GaAs dot-structures three-dimensionally surrounded by Al 0.4 Ga 0.6 As were fabricated. The clear photoluminescence peak from the dots with high quantum efficiency shows the usefulness of the fabrication technique for quantum dots.

Spatially and spectrally resolved imaging of GaAs quantum‐dot structures using near‐field optical technique

We present experimental result on spatially and spectrally resolved imaging of GaAs quantum dot (QD) structures using a near‐field optical microscope. Three photoluminescence (PL) peaks which originate from QD, quantum well (QW), and bulk regions were observed at liquid‐He temperature. Carriers were observed to diffuse effectively from the AlGaAs barriers to the QD and QW regions. The region of the intension carrier capture manifests itself by emitting a sharp PL peak, and is estimated to be about 300 nm.

OBSERVATION OF A SINGLE PHOTOLUMINESCENCE PEAK FROM A SINGLE QUANTUM DOT

We observed a very sharp photoluminescence peak from a single GaAs/AlGaAs quantum dot structure by using a microphotoluminescence measurement technique. The spectral linewidth was more suppressed by decreasing the excitation laser power, which is mainly due to reduction of the filling effect of quantized energy levels. The minimal spectral linewidth with low excitation laser power was 0.9 meV.