Kenji Hiruma

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.

Growth of Core–Shell InP Nanowires for Photovoltaic Application by Selective-Area Metal Organic Vapor Phase Epitaxy

We report on the formation of core–shell pn junction InP nanowires using a catalyst-free selective-area metalorganic vapor-phase epitaxy (SA-MOVPE) method. A periodically aligned dense core–shell InP nanowire array was fabricated and used in photovoltaic device applications. The device exhibited open-circuit voltage (VOC), short-circuit current (ISC) and fill factor (FF) levels of 0.43 V, 13.72 mA/cm2 and 0.57, respectively, which indicated a solar power conversion efficiency of 3.37% under AM1.5G illumination. This study demonstrates that high quality core–shell structure nanowire fabrication is possible by SA-MOVPE and that the nanowire arrays can be used in integrated nanowire photovoltaic devices.

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.

III–V Nanowires on Si Substrate: Selective-Area Growth and Device Applications

III-V nanowires (NWs) on Si are promising building blocks for future nanoscale electrical and optical devices on Si platforms. We present position-controlled and orientation-controlled growth of InAs, GaAs, and InGaAs NWs on Si by selective-area growth, and discuss how to control growth directions of III-V NW on Si. Basic studies on III-V/Si interface showing heteroepitaxial growth with misfit dislocations and coherent growth without misfit dislocations are presented. Finally, we demonstrate the integrations of a III-V NW-based vertical surrounding-gate field-effect transistor and light-emitting diodes array on Si. These demonstrations could have broad applications in high-electron-mobility transistors, laser diodes, and photodiodes with a functionality not enabled by conventional NW devices.

Structural transition in indium phosphide nanowires.

We study the catalyst-free growth of InP nanowires using selective-area metalorganic vapor phase epitaxy (SA-MOVPE) and show that they undergo transition of crystal structures depending on the growth conditions. InP nanowires were grown on InP substrates where the mask for the template of the growth was defined. The nanowires were grown only in the opening region of the mask. It was found that uniform array of InP nanowires with hexagonal cross section and with negligible tapering were grown under two distinctive growth conditions. The nanowires grown in two different growth conditions were found to exhibit different crystal structures. It was also found that the orientation and size of hexagon were different, suggesting that the difference of the growth behavior. A model for the transition of crystal structure is presented based on the atomic arrangements and termination of InP surfaces. Photoluminescence measurement revealed that the transition took place for nanowires with diameters up to 1 microm.

Growth and Characterization of InGaAs Nanowires Formed on GaAs(111)B by Selective-Area Metal Organic Vapor Phase Epitaxy

We fabricated InGaAs nanowires (NWs) in SiO2 mask openings on a GaAs(111)B substrate at growth temperatures of 600–700 °C using catalyst-free selective-area metal organic vapor phase epitaxy. At a growth temperature of 600 °C, particle-like depositions occurred, but they decreased in number and density when the growth temperature was increased to 650 °C and disappeared above 675 °C. The heights and growth rates of the NWs increased when the growth temperature was increased and the mask opening diameter was decreased from 300 to 50 nm. Photoluminescence (PL) spectra measured for the NWs indicated a blue shift in the peak from 0.95 to 1.3 eV as the growth temperature was increased from 600 to 700 °C, indicating an increase in the Ga composition from 62 to 88% in the InGaAs NWs.

Fabrication of Axial and Radial Heterostructures for Semiconductor Nanowires by Using Selective-Area Metal-Organic Vapor-Phase Epitaxy

The fabrication of GaAs- and InP-based III-V semiconductor nanowires with axial/radial heterostructures by using selective-area metal-organic vapor-phase epitaxy is reviewed. Nanowires, with a diameter of 50–300 nm and with a length of up to 10 μm, have been grown along the 〈111〉B or 〈111〉A crystallographic orientation from lithography-defined SiO2 mask openings on a group III-V semiconductor substrate surface. An InGaAs quantum well (QW) in GaAs/InGaAs nanowires and a GaAs QW in GaAs/AlGaAs or GaAs/GaAsP nanowires have been fabricated for the axial heterostructures to investigate photoluminescence spectra from QWs with various thicknesses. Transmission electron microscopy combined with energy dispersive X-ray spectroscopy measurements have been used to analyze the crystal structure and the atomic composition profile for the nanowires. GaAs/AlGaAs, InP/InAs/InP, and GaAs/GaAsP core-shell structures have been found to be effective for the radial heterostructures to increase photoluminescence intensity and have enabled laser emissions from a single GaAs/GaAsP nanowire waveguide. The results have indicated that the core-shell structure is indispensable for surface passivation and practical use of nanowire optoelectronics devices.

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.

Growth and Characterization of a GaAs Quantum Well Buried in GaAsP/GaAs Vertical Heterostructure Nanowires by Selective-Area Metal Organic Vapor Phase Epitaxy

We developed a growth method for forming a GaAs quantum well (QW) buried in GaAsP/GaAs heterostructure nanowires (NWs) by selective-area metal organic vapor phase epitaxy (SA-MOVPE). To determine the optimum growth conditions of GaAsP NWs, we varied the [(C4H9)PH2+ AsH3]/[(CH3)3Ga] ratio between 20 and 185. As a result, we could obtain NWs with good height uniformity when the ratio was 20. To form such NWs with a GaAs QW, we fabricated GaAs NWs of about 60 nm in diameter before the GaAsP growth. The NW uniformity was considerably improved by introducing GaAs growth. Photoluminescence (PL) measurements at 4.2 K indicated that the QW had a spectral peak about 150 meV higher than the acceptor-related recombination emission peak of GaAs, which is near 1.5 eV. The QW thickness estimated from the spectral peak energy of PL was 5.2 nm, which is in fair agreement with the value calculated from the GaAs growth rate.

Advances in III-V Semiconductor Nanowires and Nanodevices

Description: Semiconductor nanowires exhibit novel electronic and optical properties due to their unique onedimensional structure and quantum confinement effects. In particular, III-V semiconductor nanowires have been of great scientific and technological interest for next generation optoelectronic devices including transistors, light emitting diodes, lasers, photodetectors, and solar cells. Advances in III-V Semiconductor Nanowires and Nanodevices is an account of recent progress in the synthesis, characterization, physical properties, device fabrication, and applications of binary compound and ternary alloy III-V semiconductor nanowires. Each chapter is prepared by renowned experts in the field, describing the current state of knowledge and key areas of research. The book is written at the expert level, but also serves as a guide for researchers or graduate students aiming to enter semiconductor research.