Shinjiroh Hara

Control of InAs nanowire growth directions on Si.

We report on control of growth directions of InAs nanowires on Si substrate. We achieved to integrate vertical InAs nanowires on Si by modifying initial Si(111) surface in selective-area metal-organic vapor phase epitaxy with flow-rate modulation mode at low temperature. Cross-sectional transmission electron microscope and Raman scattering showed that misfit dislocation with local strains were accommodated in the interface.

GaAs/AlGaAs Core Multishell Nanowire-Based Light-Emitting Diodes on Si

We report on integration of GaAs nanowire-based light-emitting-diodes (NW-LEDs) on Si substrate by selective-area metalorganic vapor phase epitaxy. The vertically aligned GaAs/AlGaAs core-multishell nanowires with radial p-n junction and NW-LED array were directly fabricated on Si. The threshold current for electroluminescence (EL) was 0.5 mA (current density was approximately 0.4 A/cm(2)), and the EL intensity superlinearly increased with increasing current injections indicating superluminescence behavior. The technology described in this letter could help open new possibilities for monolithic- and on-chip integration of III-V NWs on Si.

Single GaAs/GaAsP coaxial core-shell nanowire lasers.

Highly uniform GaAs/GaAsP coaxial nanowires were prepared via selective-area metal organic vapor phase epitaxy. Photoluminescence spectra from a single nanowire indicate that the obtained heterostructures can produce near-infrared (NIR) lasing under pulsed light excitation. The end facets of a single nanowire form a natural mirror surface to create an axial cavity, which realizes resonance and give stimulated emission. This study is a considerable advance toward the realization of nanowire-based NIR light sources.

Selective-area growth of vertically aligned GaAs and GaAs/AlGaAs core–shell nanowires on Si(111) substrate

We report on selective-area growth of vertically aligned GaAs nanowires on Si(111) substrate. Modification of the initial Si(111) surface by pretreatment under an AsH(3) atmosphere and low-temperature growth of GaAs were important for controlling the growth orientations of the GaAs nanowire on the Si(111) surface. We also found that the size of openings strongly affected the growth morphology of GaAs nanowires on Si(111). Small diameter openings reduced the antiphase defects and improved the optical properties in the GaAs nanowires. Moreover, we realized coherent growth without misfit dislocation at the GaAs/Si interface. Finally, we demonstrated fabrication of a GaAs/AlGaAs core-shell nanowire array on a Si surface and revealed that the luminescence intensity was markedly enhanced by passivation effects. These results are promising for future III-V nanowire-based optoelectronic integration on Si platforms.

Vertical Surrounding Gate Transistors Using Single InAs Nanowires Grown on Si Substrates

We report on the fabrication and characterization of vertical InAs nanowire channel field effect transistors (FETs) with high-k/metal gate-all-around structures. Single InAs nanowires were grown on Si substrates by the selective-area metalorganic vapor phase epitaxy method. The resultant devices exhibited n-channel FET characteristics with a threshold voltage of around -0.1 V. The best device exhibited maximum drain current (I DSmax/w G), maximum transconductance (g mmax/w G), on–off ratio (I ON/OFF), subthreshold slope (SS) of 83 µA/µm, 83 µS/µm, 104, and 320 mV/decade, respectively, for a nanowire diameter of 100 nm.

Characterization of Fabry-Pérot microcavity modes in GaAs nanowires fabricated by selective-area metal organic vapor phase epitaxy

The authors present the formation of Fabry-Perot cavity in single GaAsnanowire prepared by selective-area metal organic vapor phase epitaxy. The grownnanowires with hexagonal cross section are highly uniform and vertically oriented. Microphotoluminescence measurements of single GaAsnanowire exhibit periodic peaks in the intensity, which are suggestive of the longitudinal modes of a Fabry-Perot cavity. The cavity is formed along the length of the nanowire and the (111) facets of both ends act as reflecting mirrors. Additionally, optical waveguides in GaAsnanowires were also observed.

Crystallographic Structure of InAs Nanowires Studied by Transmission Electron Microscopy

Crystallographic structure of InAs nanowires, which were grown by selective-area metalorganic vapor phase epitaxy on (111)B-oriented substrates, was investigated by transmission electron microscopy (TEM). The TEM images showed that the nanowires had many stacking faults along the growth direction. Statistical analysis of the atomic-layer stacking showed that InAs nanowires contained both zincblende and wurtzite crystal phases, whose transition took place in every one to three monolayers. This specific crystal phase transition resulted in peculiar electron diffraction patterns. The stacking of the atomic layers had no distinct correlation with the diameter of the nanowires.

Formation and photoluminescence characterization of quantum well wires using multiatomic steps grown by metalorganic vapor phase epitaxy

Abstract GaAs/AlGaAs quantum well wires (QWWs) were successfully fabricated using multiatomic steps on GaAs vicinal substrates by metalorganic vapor phase epitaxy (MOVPE). Coherent multiatomic steps with extremely straight step edges were observed on GaAs and AlGaAs epitaxially grown layers on vicinal substrates over a wide observation area by atomic force microscopy (AFM). Formation of QWW structures is due to the fact that the GaAs growth rate on AlGaAs with multiatomic steps is much larger at the corners of steps than on the terraces. GaAs QWWs at the corners of steps accompanied by quantum wells (QWs) on the terraces were observed in cross-sectional transmission electron microscope (TEM) images. Photoluminescence (PL) of QWWs was measured at 20 K. The PL peak energy of the QWW structures grown on 5.0°-misoriented substrates was 23 me V smaller than that of a reference QW structure on an exactly oriented substrate. Since the total amount of the grown material is basically the same for both structures, this peak energy shift indicates the formation of quantum-wire-like structures at the corners of multiatomic steps. Furthermore, this observed red shift is in good agreement with a simple theoretical estimate of the QWW structures observed by TEM. These results suggest that the present novel fabrication method of QWWs is very promising for the formation of uniform nano-meter size quantum wires without any processing damage.

Quantum Well Wire Fabrication Method Using Self-Organized Multiatomic Steps on Vicinal (001) GaAs Surfaces by Metalorganic Vapor Phase Epitaxy

Coherent multiatomic steps with extremely straight edges are naturally formed on vicinal (001) GaAs surfaces during metalorganic vapor phase epitaxial growth. GaAs quantum well wires (QWWs) are formed on these self-organized multiatomic steps. In our previous study, a thin AlGaAs layer was grown on GaAs with multiatomic steps as a lower barrier of QWWs. However, the height and spacing of the steps slightly fluctuate on AlGaAs layer surfaces. Therefore, in this experiment, AlAs layer instead of AlGaAs layer was used as a lower barrier layer to improve the uniformity of the height and spacing of the steps. Atomic force microscopy observations and photoluminescence (PL) measurements at 20 K revealed that the underlying coherent GaAs multiatomic steps were well traced by the AlAs barrier layer rather than the AlGaAs barrier layer. Furthermore, we measured the polarization anisotropy of the PL spectra from the QWWs with AlAs. These results suggest that uniform QWWs are successfully formed using multiatomic steps on vicinal (001) GaAs surfaces.

Hexagonal ferromagnetic MnAs nanocluster formation on GaInAs∕InP (111)B layers by metal-organic vapor phase epitaxy

The authors report the self-assembly of hexagonal MnAs nanoclusters on GaInAs (111)B surfaces by metal-organic vapor phase epitaxy. The ferromagnetic behavior of the nanoclusters dominates the magnetic response of the samples when magnetic fields are applied in a direction parallel to the wafer plane. For the magnetic fields applied in a direction perpendicular to the plane, diamagnetic characteristics are dominant. The results indicate that the c axis of the nanoclusters is perpendicular to the plane, and that their a axis is in plane. They are consistent with the results of crystallographic analysis, where the nanoclusters’ c axis is shown to be along a GaInAs [−1−1−1] direction.