J. Noborisaka

Catalyst-free growth of GaAs nanowires by selective-area metalorganic vapor-phase epitaxy

We report on the fabrication of GaAs hexagonal nanowires surrounded by {110} vertical facets on a GaAs (111) B substrate using selective-area (SA) metalorganic vapor-phase epitaxial (MOVPE) growth. The substrate for SA growth was partially covered with thin SiO2, and a circular mask opening with a diameter d0 of 50–200 nm was defined. After SA-MOVPE, GaAs nanowires with a typical diameter d ranging from 50 to 200 nm and a height from 2 to 9μm were formed vertically on the substrate without any catalysts. The size of the nanowire depends on the growth conditions and the opening size of the masked substrate. A possible growth mechanism is also discussed.

Fabrication and characterization of freestanding GaAs/AlGaAs core-shell nanowires and AlGaAs nanotubes by using selective-area metalorganic vapor phase epitaxy

We fabricated GaAs∕AlGaAs core-shell nanowires by using selective-area metalorganic vapor phase epitaxy. First, GaAs nanowires were selectively grown on partially masked GaAs (111)B substrates; then AlGaAs was grown to form freestanding heterostructured nanowires. Investigation of nanowire diameter as a function of AlGaAs growth time suggested that the AlGaAs was grown on the sidewalls of the GaAs nanowires, forming GaAs∕AlGaAs core-shell structures. Microphotoluminescence measurements of GaAs and GaAs∕AlGaAs core-shell nanowires reveal an enhancement of photoluminescence intensity in GaAs∕AlGaAs core-shell structures. Based on these core-shell nanowires, AlGaAs nanotubes were formed by using anisotropic dry etching and wet chemical preferential etching to confirm the formation of a core-shell structure and to explore a new class of materials.

Electrical Characterizations of InGaAs Nanowire-Top-Gate Field-Effect Transistors by Selective-Area Metal Organic Vapor Phase Epitaxy

Single InGaAs nanowire-top-gate metal–semiconductor field-effect transistors (MESFETs) were fabricated and characterized. Silicon-doped n-InGaAs nanowires (with a typical diameter of 100 nm) were grown by catalyst-free selective-area metal–organic vapor-phase epitaxy (SA-MOVPE). The FETs of single nanowires on SiO2-coated Si substrates were fabricated by defining metal contacts at both ends of the nanowires and the metal top gate between contacts. According to the measurements of drain current–voltage and gate transfer characteristics, the top-gate MESFETs exhibited significant enhancements in device performance characteristics compared with FETs under back-gate operation; that is, a peak transconductance of 33 mS/mm and a current on–off ratio of 103 were obtained. A possibility for further improvements in FET characteristics was also considered.

Fabrication of Axial and Radial Heterostructures for Semiconductor Nanowires by Using Selective-Area Metal-Organic Vapor-Phase Epitaxy

The fabrication of GaAs- and InP-based III-V semiconductor nanowires with axial/radial heterostructures by using selective-area metal-organic vapor-phase epitaxy is reviewed. Nanowires, with a diameter of 50–300 nm and with a length of up to 10 μm, have been grown along the 〈111〉B or 〈111〉A crystallographic orientation from lithography-defined SiO2 mask openings on a group III-V semiconductor substrate surface. An InGaAs quantum well (QW) in GaAs/InGaAs nanowires and a GaAs QW in GaAs/AlGaAs or GaAs/GaAsP nanowires have been fabricated for the axial heterostructures to investigate photoluminescence spectra from QWs with various thicknesses. Transmission electron microscopy combined with energy dispersive X-ray spectroscopy measurements have been used to analyze the crystal structure and the atomic composition profile for the nanowires. GaAs/AlGaAs, InP/InAs/InP, and GaAs/GaAsP core-shell structures have been found to be effective for the radial heterostructures to increase photoluminescence intensity and have enabled laser emissions from a single GaAs/GaAsP nanowire waveguide. The results have indicated that the core-shell structure is indispensable for surface passivation and practical use of nanowire optoelectronics devices.

Growth of GaAs and InGaAs nanowires by utilizing selective area MOVPE

We report on the fabrication of GaAs and InGaAs hexagonal nanowires surrounded by {110} vertical facets on GaAs (111)B and InP (111)B substrates using selective area (SA) MOVPE growth. The substrate for SA-growth was partially covered with thin SiO/sub 2/ and circular mask opening with diameter d/sup 0/ of 50/spl sim/200 nm was defined. After SA-MOVPE, GaAs or InGaAs nanowires with the typical diameter d ranging from 50 nm to 200 nm and height 2 /spl mu/m to 9 /spl mu/m was formed vertically on the substrates, depending on the growth conditions and the pattern geometry. Possible growth mechanism is also discussed.

Catalyst-free Growth and FET Application of (InGa) As Nanowires

In this paper, we report the catalyst-free growth of nanowires utilizing selective-area metalorganic vapor-phase epitaxy (SA-MOVPE) and their application to FETs. InAs nanowire FETs with Schottky gate resulted in large gate leakage current. But the leakage current was suppressed by using a MIS gate structure, and good saturation characteristics as FET were obtained.

Catalyst‐free growth of semiconductor nanowires by selective area MOVPE

We report on a novel catalyst‐free approach to form GaAs, AlGaAs and InGaAs nanowires and their arrays by selective area metalorganic vapor phase epitaxy (SA‐MOVPE). At optimized growth conditions, extremely uniform array of GaAs or InGaAs nanowires with diameter d of 100 nm to 200 nm were grown on GaAs and InP substrates, respectively. It was found the the shape (height h and size d) depends strongly on the growth conditions as well as the size d0 and pitch a of the mask opening. In particular, the height h of the pillar becomes higher as d is reduced. On the other hand, h decreases as a is increased. Based on these results, we obtained hexagonal nanowires with much smaller d (∼ 50 nm) and longer h (>6 μm) by doing SA‐MOVPE on masked substrates with smaller d0.