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Aagesen M.,Gasp Solar | Aagesen M.,Universitetsparken 5 | Holm J.V.,Universitetsparken 5 | Jorgensen H.I.,Universitetsparken 5 | Liu H.,University College London
Conference Record of the IEEE Photovoltaic Specialists Conference | Year: 2013

A strong candidate to improve the cost/efficiency ratio of solar cells is a high efficiency dual-junction solar cell composed of a silicon bottom cell and a 1.7 eV direct bandgap III-V top cell. Monolithic integration of these two materials has proven difficult due to their different material properties which produce crystal defects and cause long term degradation. Here we present novel data on the first gold free gallium arsenide phosphide (GaAsP) nanowire solar cells with a 1.7 eV bandgap grown on silicon by means of direct epitaxial growth. The nanowires are grown containing a core-shell n-i-p junction and individual nanowires has an efficiency of up to 10.2% at 1-sun, and 11.5% at 10-suns. © 2013 IEEE.

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 | 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.

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 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.

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