2017年7月27日星期四

A novel method of making high-quality vertical nanowires

A novel method of making high-quality vertical nanowires
Researchers in Japan have developed a novel way of growing high quality ferromagnetic nanowires in and on semi-conducting nanowire templates. Electron micrograph (a) shows a typical InAs nanowire template array, and (b) a heterojunction MnAs/InAs nanowire array. The ferromagnetic nanowires grow either inside (in the middle) or on top of the semiconducting nanowires, providing interesting electronic properties for future applications. Credit: Japan Society of Applied Physics (JSAP)

Researchers at Hokkaido University describe a novel method of making high quality vertical nanowires with full control over their size, density and distribution over a semi-conducting substrate. The findings are reported in the Japanese Journal of Applied Physics.

Nanowires hold interesting properties that are not found in bulk materials, making them useful in components for novel electronic and photonic devices. There is much interest in the development of vertical, free-standing nanowires, as their versatility shows great promise. However, most current designs use bottom-up fabrication techniques that result in vertical nanowires being randomly distributed on semi-conducting substrates, limiting their usability.

Now, Ryutaro Kodaira, Shinjiro Hara and co-workers at Hokkaido University have demonstrated a novel method of making high quality vertical nanowires with full control over their size, density and distribution over a semi-conducting substrate.

The team created an indium arsenide (InAs) nanowire template from which to grow the desired heterojunction nanowires, which were composed of ferromagnetic manganese arsenide (MnAs) and  InAs. In the fabrication process, they first produced the InAs nanowire template by precisely patterning circular openings in silicon dioxide thin films, which were deposited by plasma sputtering onto wafers. Next the researchers grew single InAs nanowires in each circular hole. The MnAs nanowires formed either inside (in the middle) or on top of the InAs nanowires, by a process known as 'endotaxy' – orientated crystal growth inside another crystal.

The MnAs nanowires had a hexagonal structure, exhibiting no defects or dislocations, and no contamination with other elements. The interface between the semi-conducting InAs nanowires and the ferromagnetic MnAs nanowires provides interesting possibilities for future devices. Indeed, Kodaira and Hara's team have already been using their new nanowires to carefully characterize magnetotransport properties of the nanowires for the potential fabrication of vertical spintronic device applications.

The nanowires could prove invaluable in next-generation sensing devices for electronic, photonic and bio-chemical applications. The new nanowires created by the team could widen the versatility of the  to even nano-scale spintronics.

More information: Ryutaro Kodaira et al. Synthesis and structural characterization of vertical ferromagnetic MnAs/semiconducting InAs heterojunction nanowires, Japanese Journal of Applied Physics (2016). DOI: 10.7567/JJAP.55.075503 

Provided by: Japan Society of Applied Physics



Source: Iopscience
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2017年7月19日星期三

Tuning the bandgap of InAs quantum dots by selective-area MOCVD

Abstract

In-plane bandgap energy control of InAs quantum dots (QDs) grown on GaAs substrates is demonstrated using selective-area epitaxy. Transmission electron microscopy and cathodoluminescence are used for characterization of the selectively grown dots. A single-step growth of a thin InAs quantum well and InAs QDs emitting at 1010 and 1100 nm (at 77 K) on the same wafer is demonstrated. Non-uniform growth profile is reported for the selectively grown QDs in the mask openings. Surface migration of adatoms from higher order facets to (1 0 0) facets results in enhanced deposition rates closer to the edge of the openings and vapour phase diffusion of adatoms results in density variations across the openings over length scales greater than the surface migration length of the adatoms.
Keywords:InAs wafer,
Source: Iopscience
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2017年7月7日星期五

Wafer-bonded coupled multilayer cavity with InAs quantum dots for two-color emission

Abstract

A GaAs/AlAs coupled multilayer cavity structure with InAs quantum dots (QDs) was fabricated by wafer-bonding of two cavity structures grown individually. The wafer-bonding technique is important to control the spatial distribution of nonlinear polarization for strong terahertz emission by the differential frequency generation of the two cavity modes of the coupled cavity. Three layers of self-assembled InAs QDs were inserted in a cavity grown on a (001) GaAs substrate as optical gain materials for two-color emission of the cavity mode lights. The other cavity with a GaAs cavity layer was grown on a (113)B GaAs substrate. Two-color emissions with a 3.8 THz frequency difference were successfully observed from the wafer-bonded coupled cavity by cw optical pumping at room temperature.
Keywords:InAs, InAs QDs,
Source:iopscience
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