We investigate the formations of wurtzite (WZ) SiC nano polytypes in zinc blende (ZB) SiC nanofilms hetero-grown on Si-(100) substrates via low pressure chemical vapor deposition (LPCVD) by adjusting the Si/C ratio of the introduced precursors. Through SEM, TEM, and Raman characterizations, we find that the nanofilms consist of discrete WZ SiC nano polytypes and ZB SiC polytypes composed of WZ polytypes (WZ + ZB) and disordered ZB SiC polytypes, respectively, according to Si/C ratios of 0.5, 1.5, and 3. We attribute the WZ polytype formation to being due to a kinetic mechanism based on the Si/C surface saturation control.
We investigate the triangular defects with different structural features on 4H-SiC epilayers by a Nomarski micro-scope,a Candela optical surface analyzer and ultraviolet photoluminescence(UV-PL)imaging.Both the foreign particles and the substrate scratches can cause the formation of the obtuse triangular defects.The central area of some obtuse triangular defects can have the spatially confined core,in which the in-grown stacking faults can be observed under the UV-PL imaging.In contrast,the obtuse triangular defects induced by the scratches appear in the form of band-like defects,of which the width depends on the scratch direction and reaches the maximum when the scratch direction is parallel to the step flow direction.The formation mechanisms of these obtuse triangular defects are discussed.
