Abstract
Growing high-quality and low-cost GaAs nanowires (NWs) as well as fabricating high-performance NW solar cells by facile means is an important development towards the cost-effective next-generation photovoltaics. In this work, highly crystalline, dense, and long GaAs NWs are successfully synthesized using a two-source method on non-crystalline SiO2 substrates by a simple solid-source chemical vapor deposition method. The high V/III ratio and precursor concentration enabled by this two-source configuration can significantly benefit the NW growth and suppress the crystal defect formation as compared with the conventional one-source system. Since less NW crystal defects would contribute fewer electrons being trapped by the surface oxides, the p-type conductivity is then greatly enhanced as revealed by the electrical characterization of fabricated NW devices. Furthermore, the individual single NW and high-density NW parallel arrays achieved by contact printing can be effectively fabricated into Schottky barrier solar cells simply by employing asymmetric Ni-Al contacts, along with an open circuit voltage of ~0.3 V. All these results indicate the technological promise of these high-quality two-source grown GaAs NWs, especially for the realization of facile Schottky solar cells utilizing the asymmetric Ni-Al contact.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-016-1420-y) contains supplementary material, which is available to authorized users.
Highlights
Due to the direct, suitable bandgap (1.42 eV) and its superior high carrier mobility (8000 cm2/Vs for electrons, 400 cm2/Vs for holes), GaAs materials possess a maximum theoretical single-junction photon-to-electricity conversion efficiency of ~30 %; their nanowire (NW) materials are widely adopted as fundamental building blocks for next-generation electronics and photovoltaics [1,2,3,4,5]
The diameter distribution is investigated by measuring the diameter of more than 100 NWs, where the histograms show that a similar diameter distribution is attained with a mean value of 39 nm employing both single- and two-source methods
The catalyst tip is clearly shown in the image, and after fast Fourier transformation (FFT) and energydispersive X-ray spectroscopy (EDS) analysis, the catalyst tip is composed of the Au2Ga crystal phase
Summary
Suitable bandgap (1.42 eV) and its superior high carrier mobility (8000 cm2/Vs for electrons, 400 cm2/Vs for holes), GaAs materials possess a maximum theoretical single-junction photon-to-electricity conversion efficiency of ~30 %; their nanowire (NW) materials are widely adopted as fundamental building blocks for next-generation electronics and photovoltaics [1,2,3,4,5]. Krogstrup and his group fabricated the vertically aligned single GaAs NW solar cell with an efficiency over the Shockley-Queisser limit of ~40 % due to the light concentration effect of the NWs with diameters comparable with the incident photon wavelength [8]. The illustrated efficiency is promising, the associated fabrication and material cost require a significant reduction in order to meet the requirements of third-generation costeffective photovoltaics. The equipment employed in these technologies is typically complicated, and the required single-crystalline growth substrates are
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