Abstract
Obtaining accurate structural information on epitaxial films and interfaces is nowhere more critical than in semiconductor passivation layers, where details of the atomic structure and bonding determine the nature of the interface electronic states. Various non-destructive methods have been used to investigate the structure of films and interfaces1,2,3,4,5,6, but their interpretation is model-dependent, leading occasionally to wrong conclusions. We have developed a new X-ray method for the direct determination of epitaxial structures, coherent Bragg rod analysis (COBRA). The usefulness of our technique is demonstrated by mapping, with atomic precision, the structure of the interfacial region of a Gd2O3 film grown epitaxially on a (100) GaAs substrate. Our findings reveal interesting behaviour not previously suggested by existing structural methods, in particular a lock-in of the in-plane Gd atomic positions to those of the Ga/As atoms of the substrate. Moreover, we find that the bulk stacking of the Gd2O3 atomic layers is abandoned in favour of a new structure that is directly correlated with the stacking sequence of the substrate. These results have important implications for Gd2O3 as an effective passivation layer for GaAs (ref. 7). Our work shows that the COBRA technique, taking advantage of the brilliance of insertion device synchrotron X-ray sources, is widely applicable to epitaxial films and interfaces.
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Acknowledgements
We thank the many collaborators who contributed to this work, including R. MacHarrie, L. Berman, L. Pfeiffer, H. Baltes, D. Walko, M.-W. Hong, X. Pan, T. O'Donnell and C. Cionca. This collaboration was aided by funding from the US–Israel Bi-national Science Foundation. Use of the Advanced Photon Source facilities at the MHATT-CAT and PNC-CAT beamlines was supported by the US Department of Energy, Office of Basic Energy Sciences. The experiments at MHATT-CAT Sector 7 were also supported by the National Science Foundation Frontiers of Physics Program. Correspondence and requests for materials should be addressed to R.C.
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Yacoby, Y., Sowwan, M., Stern, E. et al. Direct determination of epitaxial interface structure in Gd2O3 passivation of GaAs. Nature Mater 1, 99–101 (2002). https://doi.org/10.1038/nmat735
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DOI: https://doi.org/10.1038/nmat735
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