Time filter

Source Type

Zhang Y.,University College London | Sanchez A.M.,University of Warwick | Wu J.,University College London | Aagesen M.,Gasp Solar | And 5 more authors.
Nano Letters | Year: 2015

A quasi-3-fold composition symmetry has for the first time been observed in self-catalyzed III-V-V core-shell nanowires. In GaAsP nanowires, phosphorus-rich sheets on radial {110} planes originating at the corners of the hexagonal core were observed. In a cross section, they appear as six radial P-rich bands that originate at the six outer corners of the hexagonal core, with three of them higher in P content along <112>A direction and others along <112>B, forming a quasi-3-fold composition symmetry. We propose that these P-rich bands are caused by a curvature-induced high surface chemical potential at the small corner facets, which drives As adatoms away more efficiently than P adatoms. Moreover, their polarity related P content difference can be explained by the different adatom bonding energies at these polar corner facets. These results provide important information on the further development of shell growth in the self-catalyzed core-shell NW structure and, hence, device structure for multicomponent material systems. © 2015 American Chemical Society.


Zhang Y.,University College London | Sanchez A.M.,University of Warwick | Sun Y.,CAS Institute of Physics | Wu J.,University College London | And 6 more authors.
Nano Letters | Year: 2016

The influences of droplet size on the growth of self-catalyzed ternary nanowires (NWs) were studied using GaAsP NWs. The size-induced Gibbs-Thomson (GT) effect makes the smaller catalytic droplets have lower effective supersaturations and hence slower nucleation rates than the larger ones. Large variation in droplet size thus led to the growth of NWs with low uniformity, while a good size uniformity of droplets resulted in the production of highly uniform NWs. Moreover, thinner NWs were observed to be richer in P, indicating that P is more resistant to the GT effect than As because of a higher chemical potential inside Ga droplets. These results provide useful information for understanding the mechanisms of self-catalyzed III-V NW nucleation and growth with the important ternary III-V material systems. © 2015 American Chemical Society.


Wu J.,University College London | Li Y.,University of Tokyo | Kubota J.,University of Tokyo | Domen K.,University of Tokyo | And 9 more authors.
Nano Letters | Year: 2014

We present the wafer-scale fabrication of self-catalyzed p-n homojunction 1.7 eV GaAsP core-shell nanowire photocathodes grown on silicon substrates by molecular beam epitaxy with the incorporation of Pt nanoparticles as hydrogen evolution cocatalysts. Under AM 1.5G illumination, the GaAsP nanowire photocathode yielded a photocurrent density of 4.5 mA/cm2 at 0 V versus a reversible hydrogen electrode and a solar-to-hydrogen conversion efficiency of 0.5%, which are much higher than the values previously reported for wafer-scale III-V nanowire photocathodes. In addition, GaAsP has been found to be more resistant to photocorrosion than InGaP. These results open up a new approach to develop efficient tandem photoelectrochemical devices via fabricating GaAsP nanowires on a silicon platform. © 2014 American Chemical Society.


PubMed | Gasp Solar, CAS Institute of Physics, University of Warwick and University College London
Type: Journal Article | Journal: Nano letters | Year: 2016

The influences of droplet size on the growth of self-catalyzed ternary nanowires (NWs) were studied using GaAsP NWs. The size-induced Gibbs-Thomson (GT) effect makes the smaller catalytic droplets have lower effective supersaturations and hence slower nucleation rates than the larger ones. Large variation in droplet size thus led to the growth of NWs with low uniformity, while a good size uniformity of droplets resulted in the production of highly uniform NWs. Moreover, thinner NWs were observed to be richer in P, indicating that P is more resistant to the GT effect than As because of a higher chemical potential inside Ga droplets. These results provide useful information for understanding the mechanisms of self-catalyzed III-V NW nucleation and growth with the important ternary III-V material systems.


Zhang Y.,University College London | Aagesen M.,Universitetsparken 5 | Aagesen M.,Gasp Solar | Holm J.V.,Universitetsparken 5 | And 3 more authors.
Nano Letters | Year: 2013

We realize the growth of self-catalyzed GaAsP nanowires (NWs) on silicon (111) substrates using solid-source molecular beam epitaxy. By optimizing the V/III and P/As flux ratios, as well as the Ga flux, high-crystal-quality GaAsP NWs have been demonstrated with almost pure zinc-blende phase. Comparing the growth of GaAsP NWs with that of the conventional GaAs NWs indicates that the incorporation of P has significant effects on catalyst nucleation energy, and hence the nanowire morphology and crystal quality. In addition, the incorporation ratio of P/As between vapor-liquid-solid NW growth and the vapor-solid thin film growth has been compared, and the difference between these two growth modes is explained through growth kinetics. The vapor-solid epitaxial growth of radial GaAsP shell on core GaAsP NWs is further demonstrated with room-temperature emission at ∼710 nm. These results give valuable new information into the NW nucleation mechanisms and open up new perspectives for integrating III-V nanowire photovoltaics and visible light emitters on a silicon platform by using self-catalyzed GaAsP core-shell nanowires. © 2013 American Chemical Society.


Zhang Y.,University College London | Wu J.,University College London | Aagesen M.,Gasp Solar | Holm J.,Gasp Solar | And 4 more authors.
Nano Letters | Year: 2014

The growth of self-catalyzed ternary core-shell GaAsP nanowire (NW) arrays on SiO2 patterned Si(111) substrates has been demonstrated by using solid-source molecular beam epitaxy. A high-temperature deoxidization step up to ∼900 °C prior to NW growth was used to remove the native oxide and/or SiO2 residue from the patterned holes. To initiate the growth of GaAsP NW arrays, the Ga predeposition used for assisting the formation of Ga droplets in the patterned holes, was shown to be another essential step. The effects of the patterned-hole size on the NW morphology were also studied and explained using a simple growth model. A lattice-matched radial GaAsP core-shell NW structure has subsequently been developed with room-temperature photoluminescence emission around 740 nm. These results open up new perspectives for integrating position-controlled III-V NW photonic and electronic structures on a Si platform. © 2014 American Chemical Society.


Zhang Y.,University College London | Wu J.,University College London | Aagesen M.,Gasp Solar | Liu H.,University College London
Journal of Physics D: Applied Physics | Year: 2015

III-V nanowires (NWs) have been envisioned as nanoscale materials for next-generation technology with good functionality, superior performance, high integration ability and low cost, because of their special growth modes and unique 1D structure. In this review, we summarize the main challenges and important progress of the fabrication and applications of III-V NWs. We start with the III-V NW growth, that significantly influences the NW morphology and crystal quality. Attention is then given to the fabrication of some advanced III-V structures composed of axial and radial junctions. After that, we review the advantages, challenges, and major breakthroughs of using III-V NWs as solar energy harvesters and light emitters. Finally, we attempt to give a perspective look on the future development trends and the remaining challenges in the research field of III-V NWs. © 2015 IOP Publishing Ltd.


The application discloses a technique for fabricating gallium-arsenide-phosphorous (GaAsP) nanostructures using gallium-assisted (Ga-assisted) Vapour-Liquid-Solid (VLS) growth, i.e. without requiring gold catalyst particles. The resulting Ga-assisted GaAsP nanostructures are free of gold particles, which renders them useful for optoelectronic applications, e.g. as a junction in a solar cell. The Ga-assisted GaAsP nanostructures can be fabricated with a band gap in the range 1.6 to 1.8 eV (e.g. at and around 1.7 eV).


The present invention provides a reproducible preliminary in-situ oxide removal step for patterned self-assisted III-V semiconductor nanowire growth. Here in-situ means located within the same treatment environment or apparatus as the nanowire growth process, e.g. with a molecular beam epitaxy (MBE) apparatus or the like. Providing an in-situ process may prevent the formation of a thin oxide layer during transfer of the substrate into the nanowire growth apparatus.


Loading Gasp Solar collaborators
Loading Gasp Solar collaborators