Characterization and Growth Mechanism of B 12 As 2 Epitaxial Layers Grown on (1-100) 15R-SiC
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1069-D08-03
Characterization and Growth Mechanism of B12As2 Epitaxial Layers Grown on (1-100) 15R-SiC Hui Chen1, Guan Wang1, Michael Dudley1, Zhou Xu2, James. H. Edgar2, Tim Batten3, Martin Kuball3, Lihua Zhang4, and Yimei Zhu4 1 Department of Materials Science and Engineering, Stony Brook University, Stony Brook, NY, 11794 2 Department of Chemical Engineering, Kansas State University, Manhattan, KS, 66506 3 H.H. Wills Physics Laboratory, University of Bristol, Bristol, BS8 1TL, United Kingdom 4 Center for Functional Materials, Brookhaven National Laboratory, Upton, NY, 11973 ABSTRACT A systematic study of the heteroepitaxial growth of B12As2 on m-plane 15R-SiC is presented. In contrast to previous studies of B12As2 on other substrates, including (100) Si, (110) Si, (111) Si and (0001) 6H-SiC, single crystalline and untwinned B12As2 was achieved on mplane 15R-SiC. Observations of IBA on m-plane ( 1100 )15R-SiC by synchrotron white beam xray topography (SWBXT) and high resolution transmission electron microscopy (HRTEM) confirm the good quality of the films on the 15R-SiC substrates. The growth mechanism of B12As2 on m-plane 15R-SiC is discussed. This work demonstrates that m-plane15R-SiC is potentially a good substrate choice to grow high quality B12As2 epilayers. INTRODUCTION Icosahedral boron arsenide (B12As2) is a wide band gap semiconductor (3.47eV) and is potentially useful for devices operating in high electron radiation environments. An attractive possible application for B12As2 is for beta cells, which are capable of producing electrical energy by coupling a radioactive beta emitter to a semiconductor junction [1-6]. The properties of B12As2 are associated with its unique crystal structure and stiff bonding. B12As2 is based on twelve-boron-atom icosahedra, which reside at the corners of an α-rhombohedral unit cell, and two-atom As-As chains lying along the rhombohedral [111] axis. Each boron atom occupies a vertex of an icosahedra, and is bonded to five other B atoms as well as either an As atom or another icosahedron [1, 4]. In the absence of native substrates of B12As2, it is necessary to grow B12As2 as heteroepitaxial films on substrates with compatible structural parameters. To date, this has been attempted on substrates with higher symmetry than B12As2 such as on Si and 6H-SiC [4, 5-9]. However, growth of a lower symmetry epilayer on a higher symmetry substrate often produces structural variants in the film that are related to each other by a symmetry operation that is present in the substrate but absent in the epilayer. A theoretical treatment of this phenomenon, which has been referred to as degenerate epitaxy [10,11]. For substrate crystals with a multiatom basis, this list of symmetry operations must be extended to include glide planes with translation parallel to the surface. For the case of B12As2 grown on Si with (100), (110) and (111) orientation and (0001) 6H-SiC, rotational and translational variants are both predicted and observed [4, 9]. Single terrace behavior can be diminished by surface
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