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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 and optical devices.

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...

Molecular beam epitaxy (MBE) of Si atoms onto a Si(001) 1×2 surface is investigated using reflection electron microscopy. A 1×2 surface with wide 1×2 and narrow 2×1 terraces is prepared by passing a direct current from the down side to the up side at the surface steps. After sample heating to 900 °C using an alternating current without deposited Si atoms, the 1×2 surface changes to a double-domain surface, where the width of the 2×1 terraces is approximately equal to that of the 1×2 terraces. With MBE, however, the 1×2 surface remains the 1×2 surface, and the double-monolayer-height islands with an approximately circular shape are stably formed on it.

A 59Co nuclear magnetic resonance measurement and a transmission electron microscope observation are utilized to investigate the compositional distribution of Co‐Cr films with and without heat treatment. The spin‐echo spectra of evaporated films are found to be entirely different from those of Co‐Cr alloy powders. The spectra of films comprise a very complicated hyperfine field distribution and the resonant frequencies are much higher than those of powder samples, implying the existence of various kinds of segregation regions typical of a film. Chrysanthemumlike patterns, which disappear with heat treatment, are also observed for chemically etched films. This disappearance is accompanied by the disappearance of the highest‐frequency resonant line.

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.

Crystallinity of InGaPAs layers grown on GaAs substrates by liquid phase epitaxy has been examined by observing equal thickness fringes in transmission electron microscopy. Even InGaPAs layers within the theoretically immiscible composition region are found to be of one phase without compositional fluctuation. Phase separation, which can theoretically occur, is not found. However, crystallinity is generally inferior, and this inferiority increases as the epitaxial layer grows. The substrate‐induced stabilization effect seems to produce high quality crystals in the immiscible region only in the initial stage of epitaxial growth. It is also found that immiscibility affects InGaPAs layers grown on GaAs substrates to a greater extent than those grown on InP substrates.

The relation between growth temperature and ordered structures in Ga0.5In0.5P grown using organometallic vapor phase expitaxy is investigated using transmission electron diffraction, electroreflectance, and Raman scattering measurements. It is found that generation of the ordered structure is not related to the immiscibility of this alloy and that the ordered structures do not simply represent ‘‘sublattice ordering.’’ The anomalous band gap may be a consequence of the variation in the atomic arrangement of neighboring atoms, but not of the long‐range ordered structure itself.