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Published May 28, 2013 | Published
Journal Article Open

Energy-band alignment of II-VI/Zn_(3)P_2 heterojunctions from x-ray photoemission spectroscopy


The energy-band alignments for zb-ZnSe(001)/α-Zn_(3)P_2(001), w-CdS(0001)/α-Zn_(3)P_2(001), and w-ZnO(0001)/α-Zn_(3)P_2(001) heterojunctions have been determined using high-resolution x-ray photoelectron spectroscopy via the Kraut method. Ab initio hybrid density functional theory calculations of the valence-band density of states were used to determine the energy differences between the core level and valence-band maximum for each of the bulk materials. The ZnSe/Zn_(3)P_2 heterojunction had a small conduction-band offset, ΔEC, of −0.03 ± 0.11 eV, demonstrating a nearly ideal energy-band alignment for use in thin-film photovoltaic devices. The CdS/Zn_(3)P_2 heterojunction was also type-II but had a larger conduction-band offset of ΔEC = −0.76 ± 0.10 eV. A type-III alignment was observed for the ZnO/Zn_(3)P_2 heterojunction, with ΔEC = −1.61 ± 0.16 eV indicating the formation of a tunnel junction at the oxide–phosphide interface. The data also provide insight into the role of the II-VI/Zn_(3)P_2 band alignment in the reported performance of Zn_(3)P_2 heterojunction solar cells.

Additional Information

© 2013 AIP Publishing LLC. Received 18 March 2013; accepted 9 May 2013; published online 23 May 2013. This work was supported by the Dow Chemical Company and by the Department of Energy, Office of Basic Energy Sciences under Grant No. DE-FG02-03ER15483. Computations were performed on the HECToR supercomputer through membership of the HPC Materials Chemistry Consortium under EPSRC (Grant No. EP/F067496), as well as the Kelvin supercomputer as maintained by TCHPC and supported by SFI through the PI programme (Grant Nos. 06/IN.1/I92 and 06/IN.1/I92/EC07). The authors would like to thank Joseph Beardslee for his assistance with the Kratos XPS measurements. J.P.B. acknowledges the NSF for a graduate research fellowship. D.O.S. acknowledges the Ramsay Memorial Trust and University College London for a Ramsay Fellowship.

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