We present a bidirectional growth mode of InP nanowires grown by selective-area metalorganic vapor-phase epitaxy (SA-MOVPE). We studied the effect of the supply ratio of DEZn ([DEZn]) on InP grown structure morphology and crystal structures during the SA-MOVPE. Two growth regimes were observed in the investigated range of the [DEZn] on an InP(111)B substrate. At low [DEZn], grown structures formed tripod structures featuring three nanowires branched toward the [111]A directions. At high [DEZn], we obtained hexagonal pillar-type structures vertically grown on the (111)B substrate. These results show that the growth direction changes from [111]A to [111]B as [DEZn] is increased. We propose a growth mechanism based on the correlation between the incident facet of rotational twins and the shapes of the grown structures. Our results bring us one step closer to controlling the direction of nanowires on a Si substrate that has a nonpolar nature. They can also be applied to the development of InP nanowire devices.

The growth mechanism of GaAs nanowires (NWs) grown on polycrystalline silicon (poly-Si) thin films using selective-area metalorganic vapor-phase epitaxy was investigated. Wire structures were selectively grown in the mask openings on a poly-Si substrate. The appearance ratio of wire structures strongly depended on the growth conditions and deposition temperature of the poly-Si substrate. Evaluation of the grown shapes and growth characteristics revealed that GaAs NWs grown on a poly-Si substrate have the same growth mechanism as conventional GaAs NWs grown on a single-crystalline GaAs or Si substrate. Experiments showed that the wire structure yield can be improved by increasing the Si grain size and/or increasing the Si deposition temperature. The growth model proposed for understanding NW growth on poly-Si is based on the mask opening size, the Si grain size, and the growth conditions. The ability to control the growth mode is promising for the formation of nanowires with complex structures on poly-Si thin layers.

We demonstrated the formation of all-wurtzite (WZ) InP/AlInP core-multishell (CMS) nanowires (NWs) by selective-area growth with the crystal structure transfer method. The CMS NWs consisting of an AlInP-based double heterostructure showed that the crystal structure of the multishell succeeded to the WZ phase from the WZ InP NW by the crystal structure transfer method. Transmission electron microscopy revealed that the core-shell interface had a few stacking faults due to lattice mismatch. In addition, lattice constants of WZ AlInP with a variation of Al content were determined by X-ray diffraction reciprocal space mappings, and the WZ AlInP shell had tensile strain along the c-axis. The WZ AlInP shells (Al content: 25-54%) showed cathode luminescence emissions at 1.6-2.1 eV, possibly related to In-rich domains due to composition fluctuation in the WZ AlInP shell.

A GaP nanowire is promising from the viewpoint of device applications because when its crystal phase is changed from zinc blende (ZB) to wurtzite (WZ), its band gap changes from indirect to direct. GaP in the WZ phase is theoretically and experimentally shown to have the possibility of "green" emission. Here we report on the growth of WZ GaP in InP/GaP core-shell nanowires by selective-area metal-organic vapor-phase epitaxy (SA-MOVPE). WZ InP nanowires were used as a template for transferring the WZ structure to GaP. Transmission electron microscopy revealed that WZ GaP was grown on the sidewalls of the InP core in the lateral <-211> direction and that ZB GaP was grown on the top of the InP core in the axial <111>A direction. A growth model for the different crystal structures of the GaP shell is proposed from the viewpoint of the growth direction. The WZ structure is "transferred" from the InP core to the GaP shell only when GaP grows in the direction perpendicular to the WZ stacking direction of the InP core. This so-called "crystal structure transfer" can also be applied to p-and n-doped GaP and is therefore promising for fabricating WZ-GaP-based light-emitting diodes.

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We grew AlInP on two types of GaN substrate in order to transfer the wurtzite (WZ) structure to grown layers. An AlInP epitaxial layer grown on GaN with high-density stacking faults was obtained. X-ray diffraction and Raman scattering analyses indicate that the dominant crystal structure of the AlInP layer grown on GaN was WZ. Cathode luminescence measurements at 35 K revealed strong green emissions from the WZ AlInP layer, suggesting an energy band gap change from indirect to direct. These results demonstrate the potential of WZ AlInP as a new candidate for high-efficiency green emission material.

We studied the growth of indium-rich InGaP nanowires (NWs) on InP (111)A substrates by selective-area metal organic vapor phase epitaxy (SA-MOVPE). We obtained vertically aligned InGaP NWs by optimizing growth conditions, such as group III supply ratio and V/III ratio. We found that the height, diameter, shape, and composition of InGaP NWs depended significantly on the supply ratios of trimethylgallium (TMGa) and trimethylindium (TMIn). As the supply ratio of TMGa was increased, the lateral growth was drastically enhanced, and the uniformity of NWs deteriorated. Furthermore, the sidewall facets of NWs changed from {211} to {110} as the supply ratio of TMGa was increased, indicating the possibility of structural transition from wurtzite (WZ) to zinc blende (ZB). We propose a possible growth model for such lateral growth, uniformity, and structural transition. Photoluminescence (PL) measurements revealed that the Ga compositions ranged approximately from 0 to 15%. Our results show that highly uniform InGaP NWs can be grown by controlling the growth conditions.

We report on selective-area growth and characterization of wurtzite (WZ) InP/AlGaP core-multishell nanowires. Quantum well (QW) structures were fabricated in the AlGaP multishells by changing alloy compositions. Transmission electron microscopy revealed that the AlGaP multishell was grown with a WZ structure on side of the WZ InP core. The lattice constants of the WZ InP core and WZ AlGaP shell were determined by X-ray diffraction. Cathodoluminescence studies showed that the WZ AlGaP QW with an Al composition of 20% had green emissions at 2.37 eV. These results open the possibility for green light-emitting diodes using WZ AlGaP based materials. 2Color mixed RGB light-emitting diodes (LEDs) are promising candidates for future solidstate lightning and display technology due to their potential advantages in energy conversion efficiency and color rendering index (CRI). 1,2) However, achieving high efficient LEDs in the green region is challenging due to a lack of suitable semiconductor materials, which is known as the "green gap". 3,4) Non-nitride III-V materials having wurtzite (WZ) structures have recently offered a new approach to overcome this issue. Some theories predict that GaP and AlP in the WZ structures have direct band gaps in contrast to the conventional zinc blende (ZB) structures with indirect band gaps. [5][6][7] Although this approach has been experimentally demonstrated in WZ GaP 8,9) and WZ AlInP, 10) these WZ materials with quantum well (QW) structures required for LED applications have not been reported so far.In nanowire (NW) structures, radial core-multishell (CMS) NWs with QW structures are suitable structures for LED applications. 11,12) In this study, we report the growth and characterization of WZ InP/AlGaP CMS NWs with QW structures for the green color spectrum. The WZ AlGaP at an Al composition of around 20% is expected to have the band gap energy in the green spectral region according to calculations of their band structures. 6,7) The CMS NWs were synthesized by selective-area metal organic vapor phase epitaxy (SA-MOVPE). In SA-MOVPE, InP NWs can be grown with a pure WZ structure by properly adjusting the growth conditions. 13-15) Based on these WZ InP NWs, the crystal structure transfer method [16][17][18] was applied for the radial multishell growth. At first, a 20-nm-thick SiO 2 layer was deposited on an InP (111)A substrate using plasma sputtering, and the SiO 2 layer was partially removed using electron-beam (EB) lithography and wet chemical etching. The SiO 2 patterns were designed to be a periodic array of openings with a diameter of 130 nm.The SA-MOVPE was performed in a low-pressure MOVPE reactor using trimethylaluminum (TMAl), trimethylgallium (TMGa), trimethylindium (TMIn), and tertiarybutylphosphine 3 (TBP) as source materials. Prior to the growth, the native oxide on the openings was removed using thermal cleaning for 5 min at 600°C under a hydrogen and TBP ambient. After thermal cleaning, WZ InP NWs were grown for 15 min at 660°C with a V/III ratio of 18, which is t...