Characterization of SiC epilayers using high-resolution X-ray diffraction and synchrotron topography imaging
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Characterization of SiC epilayers using high-resolution X-ray diffraction and synchrotron topography imaging Xianrong Huang, Michael Dudley and Robert S. Okojie1 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 is one of the most powerful and widely used techniques for accurate characterization of the lattice parameters, mismatch, alloy composition, dopant concentrations, and thickness of epitaxial materials. In this presentation, we use a series of advanced X-ray diffraction techniques, including double-axis diffraction, triple-axis diffraction, reciprocal space mapping (RSM), and synchrotron white beam X-ray topography, to characterize highly nitrogen-doped homoepitaxial 4H-SiC epilayers. Measurements reported in this work have determined that in single crystal 4H-SiC, increasing the nitrogen doping level above 4 × 1017 cm-3 results in corresponding increase in lattice contraction. The increase in epilayer/mismatch mismatch with doping, and the corresponding strain energy, is attributed to the substitutional nitrogen incorporated preferentially in the host carbon sites of the 4H-SiC epilayer. Also, significant lattice tilts, generally along the [1120] offcut direction (8°), exist, which are believed to be induced by the Nagai epitaxial tilt.
INTRODUCTION X-ray scattering has been widely used for rapid, non-destructive characterization of thin films and multilayer structures. In particular, the various high-resolution X-ray diffraction (HRXRD) and reflectometry techniques form a comprehensive set of tools capable of extracting very detailed and accurate structural information of homo- and hetero-epitaxial systems, such as crystal perfection, lattice constants, lattice mismatch/misorientation, alloy composition, layer thickness, surface/interface roughness, density and porosity. Although HRXRD has become a routine characterization method for Si and III-V based heterostructures [1], its applications to SiC- and nitride-based epitaxial structures are still at the early stage, mainly due to the relatively low crystalline quality and complicated defect structures in these materials. In this paper, we will demonstrate that using a set of specific diffraction schemes, HRXRD techniques can also be very powerful in analysis of SiC (as well as nitride) single crystals and epitaxial structures. EXPERIMENTAL DETAILS A high-resolution diffractometer is different from a powder diffractometer in that the X-ray beam is highly monochromated and collimated by a beam conditioner before it reaches the sample. After the conditioner, the X-ray beam becomes a pseudo-plane wave, and the pseudoplane-wave diffraction process is extremely sensitive to slight strains in crystals (up to 10−5). The basic function of HRXRD is double-axis rocking curve scan (ω-scan), which may precisely
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determine the lattice parameter and thickness of each component in a nearly perfect la
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