Structure of SiC-Quantum Wells Studied by TEM and CBED
Summary and Conclusion SiC hetero-polytypic structures have been investigated by conventional and high resolution TEM and the lattice parameters of a thin cubic stripe have been determined by CBED. For the case of the stepped substrate, nearly free of defects, about 2nm thick cubic stripes are formed within the hexagonal layer. For the case of the growth on on-axis substrates, it was demonstrated that 6H/3C as well as 4H/3C stacks are formed on 6H and 4H-SiC substrates, respectively, By CBED the lattice parameters of the cubic stripe were determined to a rhom =0.4360nm a rhom = (89.78±0.02)° demonstrating the rhombohedral distortion of the 3C stripes. It might be suggested that the result is valid also for the 2nm thick cubic stripes in the multi-quantum well structures grown on the stepped SiC substrate, although such layers are generally to thin for the lattice parameter determination by CBED. Acknowledgements The authors are indebted to Dr. A. Chuvilin for the generous scientific support during his stay as guest scientist at Jena University, thank Ch. Zaubitzer for sample preparation and acknowledge the financial support of the Deutsche Forschungsgemeinschaft, Sonderforschungsbereich 196.
Refinement of crystal structure parameters using convergent‐beam electron diffraction: the low‐temperature phase of SrTiO3
The method to refine crystal structure parameters (atom positions and Debye–Waller factors) using convergent-beam electron diffraction (CBED), which is applicable to crystal structure analysis of a small specimen area down to a few nm in diameter, is studied. The line profiles of higher-order Laue-zone reflections are recorded using imaging plates. Theoretical intensities are calculated based on the dynamical theory of electron diffraction with the aid of the generalized Bethe approximation to shorten calculation time. The structural parameters are determined by fitting the experimental profiles with the theoretical ones using a nonlinear least-squares method. The present method has been applied to the low-temperature phase of SrTiO3. The structural parameter or the rotation angle of the oxygen octahedron has been determined to be \varphi = 1.12 (4)°, which shows good agreement with that obtained from electron spin resonance experiments.
SiO2 precipitate strain relief in Czochralski Si : self-interstitial emission versus prismatic dislocation loop punching
Formation of SiO2 precipitates in Czochralski Si is associated with a volume expansion of more than 100%. The needed extra volume for precipitate growth to occur is primarily supplied by emission of Si self‐interstitials (I) into the Si matrix, in balance with a compressive growth residual strain. During cooling after the anneal, an additional compressive cooling strain component also develops because of the different thermal expansion coefficients of SiO2 and Si. For precipitates grown to a sufficiently large size, the growth residual strain and/or the cooling strain can be further relieved by punching interstitial type prismatic dislocation loops into the Si matrix. Otherwise, only I emission can occur. Up to now, there have been no quantitatively determined strain values, which constitute in a given experiment a measure of the I emission efficiency on the one hand, and a basis for determining whether prismatic punching can also occur on the other. In this study, we have calculated the strain values and...