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Published June 19, 2014 | Supplemental Material
Journal Article Open

Growth Mechanism and Electronic Structure of Zn_3P_2 on the Ga-Rich GaAs(001) Surface


The growth of epitaxial Zn_3P_2 films on III–V substrates unlocks a promising pathway toward high-efficiency, earth-abundant photovoltaic devices fabricated on reusable, single-crystal templates. The detailed chemical, structural, and electronic properties of the surface and interface of pseudomorphic Zn_3P_2 epilayers grown on GaAs(001) were investigated using scanning tunneling microscopy/spectroscopy and high-resolution X-ray photoelectron spectroscopy. Two interesting features of the growth process were observed: (1) vapor-phase P4 first reacts with the Ga-rich GaAs surface to form an interfacial GaP layer with a thickness of several monolayers, and (2) a P-rich amorphous overlayer is present during the entire film growth process, beneath which a highly ordered Zn_3P_2 crystalline phase is precipitated. These features were corroborated by transmission electron micrographs of the Zn_3P_2/GaAs interface as well as density functional theory calculations of P reactions with the GaAs surface. Finally, the valence-band offset between the crystalline Zn_3P_2 epilayer and the GaAs substrate was determined to be ΔE_V = 1.0 ± 0.1 eV, indicating the formation of a hole-depletion layer at the substrate surface which may inhibit formation of an ohmic contact.

Additional Information

© 2014 American Chemical Society. Received: December 30, 2013; Revised: May 6, 2014. Publication Date (Web): May 16, 2014. This work was supported by Dow Chemical Company and by the Department of Energy. S.J. thanks to Kwanjeong Educational Foundation for support. H.K. acknowledges the support by the Global Frontier R&D Program (2013-073298) on Center for Hybrid Interface Materials (HIM) funded by the Ministry of Science, ICT & Future Planning. XPS measurement was carried out in the Molecular Materials Research Center of the Beckman Institute of Caltech.

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