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The growth of epitaxial Zn3P2 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 Zn3P2 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 Zn3P2 crystalline phase is precipitated. These features were corroborated by transmission electron micrographs of the Zn3P2/GaAs interface as well as density functional theory calculations of P reactions with the GaAs surface. Finally, the valence-band offset between the crystalline Zn3P2 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.

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. AbstractEpitaxial growth of cuprous oxide (Cu 2 O) has been achieved on (1 0 0) and (1 1 0) orientations of MgO by plasma-assisted molecular beam epitaxy. Growth was investigated using a pure oxygen plasma as well as a 90%Ar/10%O 2 plasma. Cu 2 O films grown using pure oxygen on MgO (1 0 0) have a limited growth window and typically exhibit multiple phases and orientations. Films grown on MgO (1 1 0) using pure oxygen are phase stable and predominantly (1 1 0) oriented, with some (2 0 0) orientation present. Films grown using an Ar/O 2 plasma on MgO (1 0 0) have improved phase stability and a single (1 1 0) orientation. Growth on MgO (1 1 0) using an Ar/O 2 plasma yields highly reproducible (1 1 0) oriented single phase Cu 2 O films with a much wider growth window, suggesting that this substrate orientation is preferable for Cu 2 O phase stability.

Cu2O is a potential earth-abundant alternative to established thin photovoltaic materials (CIGS, CdTe, etc.) because of its low cost, high availability, and inexpensive processing, but Cu2O has seen limited development as a photovoltaic device material owing to challenges in measurement and control of interface stoichiometry and doping. We report measurements of Cu2O interface stoichiometry and the effect of interface composition on heterojunction device performance. ZnO/Cu2O interface stoichiometry was varied by adjusting the ZnO window layer deposition conditions and stoichiometry was measured by X-ray photoelectron spectroscopy. Current-voltage characteristics of ZnO/Cu2O heterojunctions indicate open circuit voltages of Voc ~ 530 mV for devices where the Cu2O layer is stoichiometric at the interface and Voc ~ 100 mV for devices where Cu2O is nonstoichiometric at the interface.

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