Toshio Katsuyama

GROWTH AND OPTICAL PROPERTIES OF NANOMETER-SCALE GAAS AND INAS WHISKERS

The growth process, crystal structure, and optical properties of ultrathin GaAs and InAs wires (whiskers) as thin as 15–40 nm and about 2 μm long are reviewed and discussed. Experimental results for growing whiskers using Au as a growth catalyst during metalorganic vapor phase epitaxy (MOVPE) and the shape and growth direction of whiskers provide new insight into growth control of GaAs and InAs whiskers. The crystal structure of whiskers, Au behavior during MOVPE, and their growth mechanism are reviewed and discussed on the basis of transmission electron microscopic analysis. The photoluminescence spectra of GaAs wires are compared with those of a GaAs epitaxial layer, and the effect of surface treatment on the luminescence peak energy shift is discussed. The time dependent photoluminescence of GaAs wires is also discussed. The application of GaAs whiskers to light emitting devices is reviewed because a semiconductor wire structure employing quantum size effects is a very important element of electronic a...

GaAs p‐n junction formed in quantum wire crystals

A p‐n junction is formed for the first time in a cross‐sectional area of a GaAs wire crystal with a diameter of about 100 nm. Ultrafine cylindrical growth by metalorganic vapor phase epitaxy is employed for the fabrication. Current‐voltage and capacitance‐voltage characteristics confirm the formation of the p‐n junction in a narrow area at the midpoint of a wire crystal. Intensive light emission by current injection is observed at 77 K and even at room temperature. These results suggest that ultrafine optoelectronic devices with quantum‐size p‐n junction are possible.

GaAs free‐standing quantum‐size wires

Ultrathin GaAs wires as thin as 15–40 nm and about 2 μm long have been grown on a GaAs substrate by metal‐organic vapor‐phase epitaxy. The wires, which consist of whiskers, are grown between 380 and 550 °C using trimethylgallium and arsine (AsH3) as source materials. It is found that the wire growth direction is parallel to the [111] arsenic dangling‐bond direction and can be perfectly controlled by the crystallographic orientation of the GaAs substrate surface. From transmission electron microscopic analysis it is revealed that the crystal structure of the wire coincides with the zinc‐blende type for the growth temperature range of 460–500 °C, but it changes to the wurtzite type at 420 °C and temperatures higher than 500 °C. It is also found that the wires have a twin‐type structure around the [111] growth axis for zinc blende and [0001] growth axis for wurtzite. Photoluminescence study of these wires shows that the luminescence peak energy shifts to a higher energy as the wire width decreases from 100 t...

Quantum size microcrystals grown using organometallic vapor phase epitaxy

Needle‐shaped quantum size microcrystals as thin as 10 nm have been selectively grown by employing reduced pressure organometallic vapor phase epitaxy using trimethylgallium and arsine as source materials. The microcrystals grown within a SiO2 window area have their growth axes along the [111] direction. Transmission electron diffraction analysis shows that the crystal structure of microcrystals is consistent with the zinc‐blende structure of GaAs. The mechanism for growing the needle‐shaped crystals is similar to a vapor‐liquid‐solid (VLS) equilibrium phase growth model. From photoluminescence measurements at 4.2 K, it is found that the microcrystals show a very distinct spectra for free exciton and neutral acceptor‐bound exciton recombinations, meaning good crystal quality.

Self-organized growth of GaAsInAs heterostructure nanocylinders by organometallic vapor phase epitaxy

Abstract Free-standing GaAs InAs heterostructure wires as thin as 20 nm and as long as 1 μm have been formed by vapor-liquid-solid (VLS) growth during organometallic vapor phase epitaxy. The grown wires were analyzed by transmission electron microscopy, which revealed that the crystal structure of the GaAs portion coincides with that of zincblende, and the InAs portion coincides with that of wurtzite. The atomic composition along the heterojunction was also measured by energy dispersive X-ray analysis. The composition changes within a width of 5 nm at the heterojunction interface. The InAs GaAs wires show a photoluminescence peak around 1.5 eV at 14 K, which indicates significant improvement in crystal quality over conventional GaAs InAs layer structures.

Polarization dependence of light emitted from GaAs p‐n junctions in quantum wire crystals

Micro p‐n junctions are formed in GaAs nanowhiskers having diameters of about 100 nm by metalorganic vapor phase epitaxy. The result of photoluminescence measurement shows that nanowhiskers with p‐n junctions have the same confinement effect as one‐dimensional quantum wires, the average effective width of which is about 30 nm. Infrared light emitted from the whisker as a result of carrier injection is observed at 4.2 and 77 K. The most important feature of this emitted light is the dependence of its intensity on the polarization. The intensity of the emitted light whose polarization is perpendicular to the whisker axis is about 20% less than the intensity of light with parallel polarization when the influence of the electrode structure is eliminated. This value is in agreement with the theoretically predicted value of 25%, confirming that a nanowhisker is a kind of quantum wire.

A dispersion compensator using coupled defects in a photonic crystal

We propose a new type of dispersion compensator that uses the characteristics of light traveling in a coupled defect waveguide (CDW) in a photonic crystal. By using a theoretical computation based on the plane-wave method, we show that the CDW band appears within the bandgap and its characteristics are well reproduced by the tight-binding (TB) model. We calculate the wavelength dispersion of light propagating in the CDW using TB formalism. The calculated result shows an inherently large dispersion of the CDW, which enables the realization of an extremely small dispersion compensator of a few tens of millimeters in size.

Self‐organized fabrication of planar GaAs nanowhisker arrays

GaAs lateral nanowhiskers are grown on the side wall of a ridge formed on a GaAs substrate. The growth positions of the lateral nanowhiskers are controlled by a technique based on electron beam lithography. Also, lateral nanowhiskers bridging between two parallel wall surfaces are grown. These methods are potentially applicable to the fabrication of planar‐type quantum functional devices.

Low‐loss Te‐based chalcogenide glass optical fibers

Infrared optical fibers composed of Te‐based chalcogenide glass have been fabricated by using a high‐speed drawing method. Transmission loss at 10.6 μm wavelength is reduced to 1.5 dB/m.

Site‐controlled growth of nanowhiskers

The metalogranic vapor‐phase epitaxy (MOVPE) growth of site‐controlled nanowhiskers having a single preferential growth direction is accomplished by using a SiO2 window mask. A small window size (200×200 nm in this experiment) is essential for growing a single whisker from a single Au‐ seed cluster formed inside each window of the mask. The presence of the SiO2 mask greatly influences the MOVPE growth process, especially the growth direction and resultant diameter of the whiskers. This influence may be due to surface migration of the source materials or source gas diffusion near the surface from the masked region to the window region.