Kyoungwan Park

Fabrication of metal nanowire using carbon nanotube as a mask

We report on the fabrication of metal nanowires on an insulating substrate using carbon nanotubes as a new kind of mask material. By irradiating Ar+ ions of 300 eV energy on a nanotube-coated Au/Ti thin layer on a SiO2 substrate, Au/Ti nanowires were successfully formed just underneath the nanotube, indicating that the carbon nanotubes had acted as a good mask against the argon ion bombardment. The Au/Ti wire of a few nanometers in width was frequently observed among the wires of various widths. After the formation of the Au/Ti nanowires, the carbon nanotube on the metal nanowire could be removed by atomic force microscope.

Improvement of catastrophic optical damage (COD) level for high-power 0.98-μm GaInAs-GaInP laser

We investigate improvement of catastrophic optical damage (COD) level for Al-free 0.98-/spl mu/m ridge waveguide laser diodes (LDs) using the impurity induced layer disordering (IILD) process applied near the facets. The IILD is used for the purpose of forming transparent windows near both facets of the LDs utilizing its ability to increase bandgap energy of the GaInAs-GaInAsP strained quantum-well (QW) active layer. Improvement of the cod level by at least 1.65 times compared to the conventional LDs is obtained for the LDs with Si/sup +/ implantation followed by annealing at 900/spl deg/C for 10 min.

Characterization of catastrophic optical damage in Al-free InGaAs/InGaP 0.98 μm high-power lasers

Catastrophic optical damage (COD) in Al-free InGaAs/InGaP 0.98 μm lasers has been investigated using real-time electroluminescence (EL) and transmission electron microscopy (TEM). From EL images, we observed that multiple bright spots initiated from one of the facets and then propagated to the center of the cavity during the COD process. It is clarified by the TEM analysis that the propagation of bright spots resulted in 60-nm-wide Moire fringe along the cavity and the crystalline phase of the active area became polycrystalline. Highly nonradiative polycrystalline phase of the active area is the major cause of COD failure in the Al-free 0.98 μm lasers.

Erbium silicided n-type Schottky barrier tunnel transistors for nanometer regime applications

The theoretical and experimental current-voltage characteristics of Erbium silicided n-type Schottky barrier tunneling transistors (SBTTs) are discussed. The theoretical drain current to drain voltage characteristics show good correspondence with the experimental results in 10-/spl mu/m-long channel n-type SBTTs. From these results, the extracted Schottky barrier height is 0.24 eV. The experimentally manufactured n-type SBTTs with 60-nm gate lengths show typical transistor behaviors in drain current to drain voltage characteristics. The drain current on/off ratio is about 10/sup 5/ at low-drain voltage regime in drain current to gate voltage characteristics. However, the on/off ratio tends to decrease as the drain voltage increases. From the numerical simulation results, the increase of off-current is mainly attributed to the thermionic current and the increase of drain current is mainly attributed to the tunneling current.

Improvement of kink and beam steering characteristics of 0.98-μm GaInAs-GaInP high-power lasers utilizing channel ion implantation

We demonstrate a kink and beam steering free operation of 0.98-/spl mu/m GaInAs-GaInP high-power ridge waveguide (RW) lasers utilizing channel ion implantation. The ion-implanted regions along the both sides of the ridge effectively suppressed the excitation of higher order lateral modes, which causes beam steering and kink. The maximum power without beam steering and kink has been achieved over 250 mW for channel ion-implanted RW lasers with 1.8-3.7-/spl mu/m ridge width, compared to 120-mW maximum power without the channel ion implantation.

Ga-droplet-induced formation of GaAs nano-islands by chemical beam epitaxy

We report on the fabrication of self-assembled GaAs islands in a nanometer scale by chemical beam epitaxy via Ga droplet formation and subsequent supply of arsine. The density and size of GaAs nano-islands were determined by the nucleation and the growth process of Ga droplets, which were fairly sensitive to the growth condition of Ga droplets, such as the substrate temperature and the amount of TEGa supplied. Transmission electron microscopy observation showed that GaAs nano-islands with well-defined zinc-blende structure were coherently grown on the GaAs surface. Ga droplet-induced formation of GaAs nano-island is thought to be a promising method for fabricating GaAs quantum dots.

Potential applications of nanoscale semiconductor quantum devices for information and telecommunications technologies

This paper presents the results of some of our studies on nanoscale semiconductor quantum structures that bear potential capabilities to bring forth new device concepts in future information and telecommunications technologies. Experimental and theoretical results include: quantum interference effects in AlGaAs/GaAs corrugated one-dimensional wires, room temperature electron tunneling through Ag nanoclusters on silicon, and single electron tunneling through a circular quantum dot array. We also have found several new ways of forming semiconductor nanostructures such as Si nano-pillars, GaAs quantum dots, and InGaAs V-grooved quantum wires. The results collectively suggest that nanoscale semiconductor quantum structures can be useful in advanced forms of information and telecommunications technologies.

Initial stage of Ag epitaxial growth on Sb-terminated Si(111) surface

Abstract In the initial stage of Ag film growth on the Sb-terminated Si(111) surface, we have found that the surface diffusion of Ag atoms was greatly suppressed, thereby producing atomically uniform epitaxial Ag films. It was also found that the crystallographic direction of the grown Ag islands matched well with that of the substrate. The aspect ratios (height-to-diameter) of the Ag islands did not increase noticeably even after thermal annealing, which is quite different to the case of Ag growth on clean Si(111). The effects of the thermally stable Sb-terminated Si(111) surface and Sb segregation on Ag islands on the formation of atomically uniform Ag films are also discussed.

Field Emission Property of Double-walled Carbon Nanotubes Related to Purification and Transmittance

Double-walled carbon nanotubes (DWCNTs) with high purity were produced by the catalytic decomposition of tetrahydrofuran (THF) using a Fe-Mo/MgO catalyst at 800°C. The as-synthesized DWCNTs typically have catalytic impurities and amorphous carbon, which were removed by a two-step purification process consisting of acid treatment and oxidation. In the acid treatment, metallic catalysts were removed in HCl at room temperature for 5 hr with magnetic stirring. Subsequently, the oxidation, using air at 380°C for 5 hr in the a vertical-type furnace, was used to remove the amorphous carbon particles. The DWCNT suspension was prepared by dispersing the purified DWCNTs in the aqueous sodium dodecyl sulfate solution with horn-type sonication. This was then air-sprayed on ITO glass to fabricate DWCNT field emitters. The field emission properties of DWCNT films related to transmittance were studied. This study provides the possibility of the application of large-area transparent CNT field emission cathodes. (Received October 8, 2010)

Nonvolatile Memory Characteristics of Double-Stacked Si Nanocluster Floating Gate Transistor

We have studied nonvolatile memory properties of MOSFETs with double-stacked Si nanoclusters in the oxide-gate stacks. We formed Si nanoclusters of a uniform size distribution on a 5 nm-thick tunneling oxide layer, followed by a 10 nm-thick intermediate oxide and a second layer of Si nanoclusters by using LPCVD system. We then investigated the memory characteristics of the MOSFET and observed that the charge retention time of a double-stacked Si nanocluster MOSFET was longer than that of a single-layer device. We also found that the double-stacked Si nanocluster MOSFET is suitable for use as a dual-bit memory.