Accurate Lattice Constant and Mismatch Measurements of SiC Heterostructures by X-Ray Multiple-Order Reflections
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Accurate Lattice Constant and Mismatch Measurements of SiC Heterostructures by X-Ray Multiple-Order Reflections XianRong Huang, Michael Dudley, Philip G. Neudeck1, and J. Anthony Powell1 Department of Materials Science and Engineering, SUNY at Stony Brook, Stony Brook, NY 11794-2275, U.S.A. 1 NASA Glenn Research Center, Cleveland, Ohio 44135, U.S.A. ABSTRACT High-resolution X-ray diffraction (HRXRD) combined with other diffraction techniques is applied to characterize 3C SiC epilayers hoteroepitaxially grown on atomically flat mesas on 4H and 6H SiC substrates. Small-beam rocking curve scan and reciprocal mapping show extremely high crystalline perfection and homogeneity of the ideally grown 3C-SiC epilayers. Accurate lattice measurements based on X-ray multiple-order reflections reveal that: 1) no misorientation between the (0001) lattice planes across the 4H/3C or 6H/3C interface is detected, confirming the 2D nucleation mechanism of the 3C epilayer from a flat coherent interface; 2) in-plane substrate/epilayer lattice mismatch always exists, but the 3C epilayers do not correspond to a completely relaxed cubic structure, indicating that the epilayers are partially strained; 3) lattice mismatch varies for different regions, implying a complicated strain relaxation mechanism of 3C epilayers on various mesas.
INTRODUCTION The ability to reproducibly grow nearly defect-free 3C SiC crystals could enable beneficial new SiC devices to be realized, but the structural and electrical quality of the 3C polytype had previously been far inferior to commercial 4H and 6H SiC crystals. Recently, a “step-free surface heteroepitaxy” growth process was developed that can achieve 3C SiC films completely free of double positioning boundaries (DPBs) and stacking faults (SFs) on 4H and 6H SiC mesas [1-3]. These heterostructures incorporate the advantage of large heterojunction band offsets while maintaining nonpolar interfaces with extremely small lattice mismatch. Nevertheless, such heterostructures are not completely perfect in general, and slight strain relaxation can still occur at the interfaces. Understanding the strain relaxation and defect formation mechanisms during 3C SiC heteroepitaxial growth requires accurate characterization of the epilayers using highresolution X-ray diffraction (HRXRD) and other diffraction techniques. HRXRD is a comparative method mainly used to measure lattice mismatch in heterostructures [4]. In this method, only when the lattice parameters of one component (usually the substrate) are known can one derive the lattice parameters of other components. For largely mismatched heterostructures, or when the epilayer(s) and substrate differ significantly in orientation or crystal symmetry, this method usually fails. For the (0001)-orientated 3C/4H SiC heterostructure, any 0004n4H reciprocal lattice point (nearly) coincides with 0003n3C (n an arbitrary integer) in hexagonal coordinates, which enables one to measure the out-of-plane lattice mismatch (perpendicular to the interface) using symmetric refl
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