Understanding the kink formation in GaAs/InAs heterostructural nanowires

The kinks formation in heterostructural nanowires was observed to be dominant when InAs nanowires were grown on GaAs nanowires. Nanowires were grown through vapor-liquid-solid (VLS) mechanism in an MOCVD (metalorganic chemical vapor deposition) reactor. GaAs nanowires were grown in [1 1 1 ]B direction on a GaAs (1 1 1 )B substrate. When InAs nanowires grown on the GaAs nanowires, most of the InAs nanowires changed their growth directions from [1 1 1 ]B to other 〈111〉B directions. The kinks formation is ascribed to the large compressive misfit strain at the GaAs/InAs interface (7.2% lattice mismatch between GaAs and InAs) and the high mobility of indium species during MOCVD growth. The in-depth analysis of the kinks formation was done by growing InAs for short times on the GaAs nanowires and characterizing the samples. The hindrance to compressively strain InAs to form coherent layers with GaAs pushed the InAs/Au interfaces to the sides of the GaAs nanowires growth ends. New InAs/Au interfaces have generated at the sides of GaAs nanowires, due to lateral growth of InAs on GaAs nanowires. These new interfaces led the InAs nanowires growth in other 〈111〉B directions. The morphological and structural features of these heterostructural kinked nanowires were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. © 2006 IEEE.

Quantum dots and nanowires for photonics applications

We review our results on integrated photonic devices fabricated using InGaAs quantum-dots. Selective-area metal organic chemical vapor deposition (MOCVD) is used to grow the active region with quantum dots emitting at different wavelengths for fabrication of the integrated devices. We will also review the structural and optical properties of III-V nanowires, and axial and radial nanowire heterostructures grown by MOCVD. In addition to binary nanowires, such as GaAs, InAs, and InP, we have demonstrated ternary InGaAs and AlGaAs nanowires. Core-shell nanowires consisting of GaAs cores with AlGaAs shells, and core-multishell nanowires with several alternating shells of AlGaAs and GaAs, exhibit strong photoluminescence. Axial segments of InGaAs have been incorporated within GaAs nanowires to form GaAs/InGaAs nanowire superlattices.

Growth mechanism of truncated triangular GaAs nanowires

During the growth of GaAs nanowires on the {111}B GaAs substrate, truncated triangular GaAs nanowires were commonly observed in the bottom region of nanowires. Through detailed structural analysis by electron microscopy, we have determined the growth mechanism of truncated triangular GaAs nanowires. © 2006 IEEE.

Temperature dependence of photoluminescence from single core-shell GaAs-AlGaAs nanowires

Temperature-dependent polarized microphotoluminescence measurements of single GaAsAlGaAs core-shell nanowires are used to probe their electronic states. The low-temperature emission from these wires is strongly enhanced compared with that observed in bare GaAs nanowires and is strongly polarized, reflecting the dielectric mismatch between the nanowire and the surrounding air. The temperature-dependent band gap of the nanowires is seen to be somewhat different from that observed in bulk GaAs, and the PL rapidly quenches above 120 K, with an activation energy of 17 meV reflecting the presence of nonradiative defects. © 2006 American Institute of Physics.

Growth of GaAs/InAs vertical nanowires on GaAs (111)B by metalorganic chemical vapor deposition

The growth mechanism and properties of GaAs/InAs nanowires prepared by metalorganic chemical vapor deposition are investigated. Vertical InAs nanowires on GaAs (111)B substrates are successfully grown despite the large lattice mismatch (-7.2%). The crystallographic perfection of InAs nanowires is confirmed by hexagonal or triangular cross section. An interesting L-shaping of GaAs/InAs heterostructure nanowire which could be useful for novel device application is observed. © 2005 IEEE.

Semiconductor laser with a biconical waveguide

The propagation losses in the fundamental mode of a bicone made of highly reflecting metal or a dielectric of large refraction were approximately estimated using Leontovich's boundary condition. A 400-fold concentration of the energy flux density lias been obtained in a cross section which is much smaller than λ. Here, the losses are 2.5% at λ = 550 nm in an Ag bicone and 12% in a semiconductor bicone with a band gap of ≈1 eV for hv larger than the band gap. The excitation efficiency of a bicone has been estimated. While not too large, it can be increased significantly using the method proposed in the present paper. The application of the optical bicone for the multiplication of a semiconductor-laser frequency is discussed. The results obtained are also of use in scanning near-field optical microscopy and in experiments on focusing laser pulses of ultrahigh power. © 2000 Plenum/Kluwer Publishing Corporation.

Role of a high gain of the medium in superradiance generation and in observation of coherent effects in semiconductor lasers

A theoretical model of superradiant pulse generation in semiconductor laser structures is developed. It is shown that a high optical gain of the medium can overcome phase relaxation and results in a built-up superradiant state (macroscopic dipole) in an assembly of electron - hole pairs on a time scale much longer than the characteristic polarisation relaxation time T2. A criterion of the superradiance generation is the condition acmT2 > 1, where α is the gain coefficient and cm is the speed of light in the medium. The theoretical model describes both qualitatively and quantitatively the author's own experimental results.