Masamitsu Yazawa

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...

Effect of one monolayer of surface gold atoms on the epitaxial growth of InAs nanowhiskers

This letter shows that selective heteroepitaxy of nanometer‐scale InAs whiskers on SiO2‐patterned GaAs substrates [Yazawa, Koguchi, and Hiruma, Appl. Phys. Lett. 58, 1080 (1991)] is induced by surface contamination with Au resulting from the fluorocarbon plasma etching process used to etch the SiO2 mask. We demonstrate that high densities (≂1010/cm2) of InAs nanowhiskers 20–30 nm in diameter can be epitaxially grown on InAs(111)B substrates onto which 1 monolayer of Au atoms had been deposited. This wirelike growth appears to be induced by ultrafine alloy droplets generated by the reactions between Au‐clusters and InAs substrates.

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.

Heteroepitaxial ultrafine wire‐like growth of InAs on GaAs substrates

We demonstrate heteroepitaxial ultrafine wire‐like growth of InAs. Ultrafine InAs whiskers with diameters less than 20 nm are grown selectively on SiO2‐patterned GaAs substrates using metalorganic vapor phase epitaxy. These InAs nanowhiskers grow epitaxially with a growth axis parallel to the 〈111〉As dangling bond direction of the GaAs substrate surface irrespective of substrate orientation.

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.

Nanometre-sized GaAs wires grown by organo-metallic vapour-phase epitaxy

We grew GaAs wires as thin as 20?nm on a GaAs(111)B substrate using organo-metallic vapour-phase epitaxy (OMVPE), with Au as a growth catalyst. To investigate the growth characteristics, we compared two methods of depositing Au. In the first, Au was deposited by vacuum evaporation, and the deposition thickness was varied to form a planar Au layer. We found that an Au layer thickness of 1?nm was best for forming cylindrical shaped wires. Next, a new method of injecting Au onto an area of a few micrometres was tested using a focused ion beam (FIB), and this method was found to be effective for growing wires as thin as 30?80?nm. However, the wire width did not depend on the injected density of Au. We based our analysis of the results on an ion implantation model. GaAs wires with a p?n junction along the direction were formed by changing dopants from silicon to carbon during growth. We observed an optical emission with a peak intensity at the wavelength of 910?920?nm during continuous current injection into the wires at 300?K. A spectral blue-shift in the light emission and a polarization along the wire growth direction were also revealed at 77?K.

Nanocolumns composed of GaAs‐InAs jointed whiskers and SiO2 covers

A dense array of nanocolumns composed of GaAs‐InAs jointed whiskers and SiO2 covers has been fabricated on InAs substrates. The cylindrical GaAs whisker with a 20 nm diameter and 1.5 μm long is jointed on top of 0.3‐μm‐long InAs whisker by vapor‐liquid‐solid epitaxy. The nanocolumns array exhibited photoluminescence at 14 K.

The Growth Mechanism of Nanometer-scale GaAs, InAs, and AlGaAs Whiskers

Freestanding nanometer-scale whiskers composed of GaAs, InAs, and AlGaAs were grown using organometallic vapor-phase epitaxy. We found two kinds of relationship between the growth rate of the whiskers and their width depending on the growth temperature. The relationship between the growth rate and the width of the whiskers at lower temperatures can be explained by the difference between the chemical potentials in the vapor phase and in the whisker (solid phase). The minimum width of the whiskers was around 1 nm for GaAs, 4 nm for InAs, and 9 nm for AlGaAs. The relationship between the growth rate and the width of the whiskers at higher temperatures can be explained by the process of surface migration of the source material near the whiskers. In both relationships, the growth rate depended on the amount of Au in the alloy droplets used as seeds for growth. This dependence indicates that there is an optimum amount of Au for whisker growth.

Selective Growth of Ultra-low Resistance GaAs/lnGaAs for High Performance lnGaAs FETs

To minimize the source resistance of a doped-channel InGaAs heterostructure FET grown on a GaAs substrate, GaAs, InGaAs and InAs selective growth conditions are studied by metalorganic vapor phase epitaxy (MOVPE). It is found that the lowest growth temperatures with complete selectivity for InGaAs (indium composition less than 0.2) and InAs are 540 and 400°C, respectively. The contact resistance at the regrown interface measured with the transmission line model (TLM), is minimized to 5 × 10-9 ω cm2 when the Si-doped GaAs is regrown using a side contact structure. However, the contact resistance increases as the In composition in the regrown InGaAs increases. This might be due to the strain or dislocations caused by lattice mismatching between GaAs and InGaAs.