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A nano-patterning approach on silicon dioxide (SiO2) material, which could be used for the selective growth of III-V nanowires in photovoltaic applications, is demonstrated. In this process, a silicon (Si) stamp with nanopillar structures was first fabricated using electron-beam lithography (EBL) followed by a dry etching process. Afterwards, the Si stamp was employed in nanoimprint lithography (NIL) assisted with a dry etching process to produce nanoholes on the SiO2 layer. The demonstrated approach has advantages such as a high resolution in nanoscale by EBL and good reproducibility by NIL. In addition, high time efficiency can be realized by one-spot electron-beam exposure in the EBL process combined with NIL for mass production. Furthermore, the one-spot exposure enables the scalability of the nanostructures for different application requirements by tuning only the exposure dose. The size variation of the nanostructures resulting from exposure parameters in EBL, the pattern transfer during nanoimprint in NIL, and subsequent etching processes of SiO2 were also studied quantitatively. By this method, a hexagonal arranged hole array in SiO2 with a hole diameter ranging from 45 to 75 nm and a pitch of 600 nm was demonstrated on a four-inch wafer. [ABSTRACT FROM AUTHOR]

Nanowire (NW) crystal growth via the vapour–liquid–solid mechanism is a complex dynamic process involving interactions between many atoms of various thermodynamic states. With increasing speed over the last few decades many works have reported on various aspects of the growth mechanisms, both experimentally and theoretically. We will here propose a general continuum formalism for growth kinetics based on thermodynamic parameters and transition state kinetics. We use the formalism together with key elements of recent research to present a more overall treatment of III–V NW growth, which can serve as a basis to model and understand the dynamical mechanisms in terms of the basic control parameters, temperature and pressures/beam fluxes. Self-catalysed GaAs NW growth on Si substrates by molecular beam epitaxy is used as a model system. [ABSTRACT FROM AUTHOR]

Light management is of great importance in photovoltaic cells, as it determines the fraction of incident light entering the device. An optimal p-n junction combined with optimal light absorption can lead to a solar cell efficiency above the Shockley-Queisser limit. Here, we show how this is possible by studying photocurrent generation for a single core-shell p-i-n junction GaAs nanowire solar cell grown on a silicon substrate. At 1 sun illumination, a short-circuit current of 180 mA cm-2 is obtained, which is more than one order of magnitude higher than that predicted from the Lambert-Beer law. The enhanced light absorption is shown to be due to a light-concentrating property of the standing nanowire, as shown by photocurrent maps of the device. The results imply new limits for the maximum efficiency obtainable with III-V based nanowire solar cells under 1 sun illumination. [ABSTRACT FROM AUTHOR]

• A new method to manipulate the self-catalyzed droplet by altering the surface energy. • The droplet can be pinned at the nanowire tip despite the absence of planar defects. • The first self-catalysed pure zinc blende horizontal nanowires with uniform diameters. • A successful rate of 100 % has been achieved in growing horizontal nanowires. Self-catalyzed horizontal nanowires (NWs) can greatly simplify the CMOS integration processing compared with the regular vertical counterparts. However, self-catalyzed growth mode poses challenges in manipulating the droplets to produce single-crystalline horizontal NWs with a uniform diameter. Here, we demonstrated a novel method to manipulate the droplet through altering the droplet surface energy. Ga-droplet was successfully moved from top to sidewalls in GaAsP NWs by introducing Be and lowering the surface energy, and pinned at the tip despite the absence of planar defects. This can switch the <111> growth direction, with a successful rate of 100 %, from vertical to horizontal through the assistance of few sparse twins. The produced NWs tend to be bounded by low energy facets, which leads to the self-catalysed growth of horizontal NWs with a greatly improved diameter uniformity along the axis. Besides, the lowered surface energy can effectively suppress the wurtzite nucleation, producing pure zinc blende single-crystalline horizontal NWs. This study establishes an essential step toward the efficient integration of NWs into CMOS compatible devices. [ABSTRACT FROM AUTHOR]

The growth of self-catalyzed ternarycore–shell GaAsP nanowire(NW) arrays on SiO2patterned Si(111) substrates has beendemonstrated by using solid-source molecular beam epitaxy. A high-temperaturedeoxidization step up to ∼900 °C prior to NW growth wasused to remove the native oxide and/or SiO2residue fromthe patterned holes. To initiate the growth of GaAsP NW arrays, theGa predeposition used for assisting the formation of Ga droplets inthe patterned holes, was shown to be another essential step. The effectsof the patterned-hole size on the NW morphology were also studiedand explained using a simple growth model. A lattice-matched radialGaAsP core–shell NW structure has subsequently been developedwith room-temperature photoluminescence emission around 740 nm. Theseresults open up new perspectives for integrating position-controlledIII–V NW photonic and electronic structures on a Si platform. [ABSTRACT FROM AUTHOR]

Controlled and reproducible doping is essential for nanowires (NWs) to realize their functions. However, for the widely used self-catalyzed vapor-liquid-solid (VLS) growth mode, the doping mechanism is far from clear, as the participation of the nanoscale liquid phase makes the doping environment highly complex and significantly different from that of the thin film growth. Here, the doping mechanism of self-catalyzed NWs and the influence of self-catalytic droplets on the doping process are systematically studied using beryllium (Be) doped GaAs NWs. Be atoms are found for the first time to be incorporated into NWs predominantly through the Ga droplet that is observed to be beneficial for setting up thermodynamic equilibrium at the growth front. Be dopants are thus substitutional on Ga sites and redundant Be atoms are accumulated inside the Ga droplets when NWs are saturated, leading to the change of the Ga droplet properties and causing the growth of phase-pure zincblende NWs. This study is an essential step toward the design and fabrication of nanowire devices. [ABSTRACT FROM AUTHOR]

In this Letter, we demonstrate that a significant improvement of optical performance of InAs nanowires can be achieved by capping the core InAs nanowires with a thin InP shell, which successfully passivates the surface states reducing the rate of nonradiative recombination. The improvements have been confirmed by detailed photoluminescence measurements, which showed up to a 10-fold increase in the intensity of room-temperature photoluminescence from the capped InAs/InP nanowires compared to the sample with core-only InAs nanowires. Moreover, the nanowires exhibit a high stability of total photoluminescence emission strength across temperature range from 10 to 300 K as a result of strong quantum confinement. These findings could be the key to successful implementation of InAs nanowires into optoelectronic devices. [ABSTRACT FROM AUTHOR]

The III-V nanowire quantum dots (NWQDs) monolithically grown on silicon substrates, combining the advantages of both one- and zero-dimensional materials, represent one of the most promising technologies for integrating advanced III-V photonic technologies on a silicon microelectronics platform. However, there are great challenges in the fabrication of high-quality III-V NWQDs by a bottom-up approach, that is, growth by the vapor-liquid-solid method, because of the potential contamination caused by external metal catalysts and the various types of interfacial defects introduced by self-catalyzed growth. Here, we report the defect-free self-catalyzed III-V NWQDs, GaAs quantum dots in GaAsP nanowires, on a silicon substrate with pure zinc blende structure for the first time. Well-resolved excitonic emission is observed with a narrow line width. These results pave the way toward on-chip III-V quantum information and photonic devices on silicon platform. [ABSTRACT FROM AUTHOR]

We present the wafer-scale fabricationof self-catalyzed p–nhomojunction 1.7 eV GaAsP core–shell nanowire photocathodesgrown on silicon substrates by molecular beam epitaxy with the incorporationof Pt nanoparticles as hydrogen evolution cocatalysts. Under AM 1.5Gillumination, the GaAsP nanowire photocathode yielded a photocurrentdensity of 4.5 mA/cm2at 0 V versus a reversible hydrogenelectrode and a solar-to-hydrogen conversion efficiency of 0.5%, whichare much higher than the values previously reported for wafer-scaleIII–V nanowire photocathodes. In addition, GaAsP has been foundto be more resistant to photocorrosion than InGaP. These results openup a new approach to develop efficient tandem photoelectrochemicaldevices via fabricating GaAsP nanowires on a silicon platform. [ABSTRACT FROM AUTHOR]