Hiroshi Kakibayashi

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 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...

Crystal structure change of GaAs and InAs whiskers from zinc-blende to wurtzite type

Crystal structures of GaAs and InAs whiskers grown by metalorganic vapor phase epitaxy are evaluated by means of a transmission electron microscope. The whiskers are grown epitaxially on GaAs substrates with diameters of 20-100 nm and lengths of 1-5 µm. They have the following characteristics. 1) GaAs whiskers have layered structures with 2-30 nm period, that are the 111 rotating twins of the zinc-blende type. 2) InAs whiskers also have layered structures which consist of wurtzite and zinc-blende type crystals. The wurtzite type InAs is observed for the first time in this study. The volume ratio of these two types strongly depends on the growth conditions, such as substrate temperature and material gas pressure. This suggests that defect-free whiskers with a single phase that are useful for quantum wire devices can be grown by controlling the growth conditions.

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.

Ordered structure in OMVPE-grown Ga0.5In0.5P

Abstract The ordered structure of Ga and In in GaInP grown on (001) GaAs by organometallic vapor phase epitaxy (OMVPE) is investigated using high-resolution transmission electron microscopy (TEM). Cross-sectional TEM reveals that the main structure consists of ( 1 2 1 2 1 2 ) and ( 1 2 1 2 1 2 orderings. These orderings are sequences of (111) planes arranged in the order of Ga/P/In/P/ Ga/P/In/P along the [111] and [11 1 ] directions, respectively. The ordered structure may be thermodynamically stable. The OMVPE growth mechanism may partly determine ordering direction in the crystal.

Influence of growth temperature on crystalline structure in Ga0.5In0.5P grown by organometallic vapor phase epitaxy

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.

Composition dependence of equal thickness fringes in an electron microscope image of GaAs/AlxGa1−xAs multilayer structure

A new method is presented for the composition analysis of GaAs/AlxGa1-xAs multilayer structure using transmission electron microscopy. It is found that the position of equal thickness fringe observed at the edge of a cleaved chip is closely related to the composition. Change in Al composition in GaAs/AlxGa1-xAs superstructure is observed as a shift of the equal thickness fringe. Compositional abruptness at the heterointerface and compositional fluctuation in the thin layer can be estimated in the electron microscope image.

Study of Co‐Cr films for perpendicular magnetic recording using nuclear magnetic resonance

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.

Simulation studies of a composition analysis by Thickness-fringe (CAT) in an electron microscope image of GaAs/AlxGa1−xAs superstructure

The intensity distribution of thickness fringes, observed at the edge of a cleaved chip of GaAs/AlxGa1-xAs superstructure using a transmission electron microscope, was computer-simulated by means of the dynamical theory of electron diffraction. It was theoretically verified that the distance of a thickness fringe from the edge of a chip systematically changes, depending on the Al composition (experimentally found by the present authors (H. Kakibayashi and F. Nagata: Jpn. J. Appl. Phys. 24 (1985) L905)). The precise composition profile in the heterointerface and the most suitable observation condition for a composition analysis were studied using the simulation technique.

Electrical and structural properties of dislocations confined in a InGaAs/GaAs heterostructure

Electrical activation and structural defects in lattice‐mismatched InGaAs/GaAs heterostructures are studied using the capacitance‐voltage method, deep‐level transient spectroscopy, and cross‐sectional transmission electron microscopy. Confinement of structural defects is observed in an In0.2Ga0.8As/GaAs heterostructure with a relaxed InGaAs layer thicker than the thickness of the critical layer. When In composition is 0.2, where the lattice mismatch is 1.4% between InGaAs and GaAs, a two‐dimensional growth mode dominates. Misfit dislocations are formed and conduction electrons are depleted only near the InGaAs/GaAs interface. Carrier depletion is related to an electron trap with an activation energy of 0.395 eV and a capture cross section of 1×10−16 cm2 induced by deformation. Electrical evaluations show that electrical activity in the InGaAs layer does not degrade by interfacial dislocations. Therefore, a good‐quality InGaAs layer is provided though the thin layer near the interface is of poor quality. T...