Papers by Keyword: Morphological Instability

Abstract: This study reports our newly developed technology for SiC solution growth. In particular, we succeed in completely suppressing solvent inclusions, which have been a serious technological problem peculiar to the solution growth method. Then, we fabricate two-inch-diameter 4° off-axis SiC wafers without solvent inclusions. Moreover, we performed their crystal defects evaluation. It was found that our wafers were low resistance n-type 4H-SiC and contain almost no basal plane dislocation. As a result, the superior quality of our solution-grown crystal was confirmed.

Abstract: The surface morphology on the (000-1)C facet of 4H-SiC boules grown by the physical vapor transport method was examined in various scales (from millimeter to nanometer) using different types of microscopies such as differential interference contrast (DIC) optical microscopy and atomic force microscopy (AFM). The DIC optical microscope observation revealed that there exist three distinct morphological regions at the growth front of the 4H-SiC boules; they are facetted, non-facetted, and the intermediate region between them. The local inclination of the facet surface from the (000-1) basal plane increases toward the facet edge and then decreases over the intermediate region. AFM observations revealed characteristic step structures in these two regions and also that they are significantly influenced by nitrogen-doping. Based on the results, the formation mechanism of the facet morphology on 4H-SiC boules is discussed.

Abstract: The solution growth of SiC on an off-axis seed is effective on the reduction of threading dislocations. We proposed a novel method to grow a SiC crystal on an off-axis seed by top-seeded solution growth (TSSG). In our previous study, a unidirectional solution flow above a seed crystal is effective to suppress surface roughness in the growth on the off-axis seed. However, it is difficult to apply the unidirectional flow in an axisymmetric TSSG set-up. In this study, the unidirectional flow could be achieved by shifting the rotational axis away from the center of the seed crystal. As a result, the smooth surface was obtained in the wider area where the solution flow direction was opposite to the step-flow direction.

Abstract: The aim of this study is to resolve the phenomenon of formation of mesoscopic structures on the surface of heteroepitaxial thin film system due to surface diffusion by considering the effects of both surface and interface stresses. Elastic stress field caused by curved surface is solved by using the constitutive equations of linear elasticity for the bulk and surface phases. Based on the method of superposition, a boundary perturbation technique, Goursat-Kolosov complex potentials and Muskhelishvili representations, the boundary value problem is reduced to the successive solution of a system of singular and hypersingular integral equations for any order of approximation. This solution and thermodynamic approach allows us to derive a governing equation which gives the amplitude changing of a surface roughness with time.

Abstract: The morphological instability appeared at step-free 4H-SiC (0001) surfaces was investigated. The step-free surfaces were fabricated at the bottom of inverted-mesa structure by the method combining a laser digging and Si-vapor etching. By repeated Si-vapor etching treatments, randomly created crater and maze structures were cyclically appeared at the step-free surfaces. These structures were distinctly classifiable by their depths from the step-free surfaces. Crater structures have 0.2 - 0.3 nm depth and maze structures have 0.5 nm depth. The morphological evolutions indicate the process of destruction of the step-free (0001) basal plane and generation of steps from step-free surfaces in the Si-vapor etching process.

Abstract: The movement and morphological change of a solid-liquid interface in directional solidification was investigated during two sounding rocket flights. By using the transparent binary alloy Succinonitrile-Acetone the dynamic processes at the solidification front could be observed directly. Both the planar interface growth, the onset of instability and the characteristic features of the interface morphology, i.e. the evolution of the primary spacing and amplitudes of the cells and dendrites were evaluated. The comparison with a calculation of the morphological instability based on the theoretical model of Warren and Langer showed a good agreement concerning the critical time and velocity of the solidification front.