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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 (11̄0) side walls.

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Magnetophotoluminescence spectra of GaAs quantum wires with lateral and vertical dimensions of 20 and 10 nm, respectively, were measured up to 40 T with three orthogonal magnetic field configurations. The observed photoluminescence peak shift with increase of applied magnetic field was strongly dependent on the direction of magnetic field, which directly demonstrates the existence of two-dimensional confinement in the quantum wires. It was found that the excitons were anisotropically shrunk in the quantum wires, and that the observed magnetic energy shift was consistent with the size of the quantum wire structure. PACS numbers: 73.20.Dx, 78.20.Ls, 78.55.Cr, 78.65.Fa Two-dimensional (2D) confinement of carriers in quantum wires (QWRs) is an important phenomenon in physics, as well as for applications to semiconductor lasers and other functional devices [1,2]. Many workers have intensively investigated the realization of QWR structures with various fabrication techniques [3-7]. In situ fabrication techniques embedding QWRs in barriers are promising for reducing damage or impurities and the resulting nonradiative recombination at the surfaces or the interfaces. Recently, by the growth technique of metalorganic chemical vapor deposition (MOCVD) on V grooves, GaAs QWRs embedded in AlGaAs have been produced [4,8,9]. The QWRs exhibited clear cathodoluminescence (CL) [9] or photoluminescence (PL) spectra [10], and an anisotropic polarization dependence of the PL excitation (PLE) spectra.In order to obtain evidence of 2D confinement in QWRs, the blueshift or polarization anisotropy of PL or PLE spectra has been studied [9-12]. However, it is pointed out that the blueshift or the polarization anisotropy itself is not a proof of 2D confinement [13]. Magneto-optical measurements were also carried out for QWRs prepared by the etching of quantum wells (QWLs), and the confinement energy or the exciton binding energy was estimated [14,15]. However, because the values were estimated from data in low magnetic fields and for one magnetic field direction, they were largely dependent on the theory with simplified approximations and fitting parameters. In order to clarify 2D confinement experimentally and more clearly, measurements with a three-dimensional variation of the direction of strong external fields on well-defined QWRs, and consistency among the data, are required.In this paper, we report high field magneto-PL (MPL) spectra of in situ fabricated GaAs QWRs, where the orientation of applied magnetic fields was varied in three independent directions relative to the QWRs. We observed a clear dependence of the PL spectra on both the magnitude and the direction of the magnetic fields. It was found that the excitons were anisotropically shrunk in the QWRs, and that the size of the QWRs estimated from the energy changes was consistent with that determined by the high-resolution secondary electron image (SEI) of the QWR structure.A schematic cross section and the SEI of the sample in this work are shown in Figs. 1 (a) and 1 (b), resp...

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.