Papers by Author: Xiu Fang Chen

Abstract: Graphene, as strict two-dimensional material, exhibits exceptionally good electronic properties. In this paper, graphene was prepared on SiC substrates at different temperature based on two types of pre-treated surface. The surface morphology was characterized by atomic force microscopy (AFM) and scanning electronic microscopy (SEM). The results on SiC surface pre-treatment showed that chemical mechanical polishing (CMP) was an effective surface treatment method for reproducible and controlled growth of graphene. Images of the Si-surface revealed that the thickness of graphitic layers increased with annealing temperature. Meanwhile, a mesh-like network of wrinkles tended to tent-like features with the increase of temperature. The residual stresses, average crystallite size and number of graphene layers were analyzed by Raman spectroscopy. Little shift of 2D-band indicated the presence of certain stresses. Results among four samples showed that graphene layers grown on MP C-surface substrates had the thickest layers，contained the smallest average crystallite size L_a and exhibited no stresses. While graphene layers grown on Si-surface under 1600°C built upon compressive stresses, exhibited largest L_a and least number of graphene layers, indicating perfect quality.

Abstract: Contactless resistivity mapping, scanning electron microscope (SEM) and confocal laser microscope have been used to study the relationship of the resistivity and the etching behavior of the semi-insulating 6H-SiC wafer. Evidence is presented that the morphologies of the etch pits vary significantly with the impurity concentrations. The V impurity strongly affects the etch rates of edge, screw and mixed dislocations. For the dislocation containing the Burgers vector component of <0001>, its vertical etch rate is enhanced distinctly. In contrast, the horizontal etch rate becomes larger for the dislocation containing the Burgers vector component of < >. The shape of the etch pits reflects the Fermi level of the semi-insulating wafer and the net shallow impurity concentration.

Abstract: 4H-SiC single crystal with a diameter of 1.5’’ has been grown by the seed sublimation method. Regions of mixed polytypes are assessed by high resolution X-ray diffractometry with the asymmetrical diffraction geometry. Multiple reflections are observed from the rocking curve measurements of a longitudinal cut 4H-SiC slice. Those reflections are indexed to be 2131 and 2131 of 4H-SiC, 2130 , 2131 , 2131 , 2132 and 2132 of 6H-SiC, 2131 , 2132 , 2134 , 2135 and 2137 of 15R-SiC respectively based on the lattice constants of different polytypes in SiC crystal. It is believed that the polytypes can be identified by high resolution X-ray diffractometry.

Abstract: 6H-SiC ingots were grown with different growth interfaces at different rates via the sublimation method. A model for the step flow growth mechanism is proposed to interpret the occurrence of 15R-SiC inclusions in the 6H-SiC single crystal. The results show that the 15R-SiC occurs more easily on the convex and the concave interface than on the slight convex interface and 15R-SiC inclusion also occurs when the growth rate of 6H-SiC exceeds the critical rate of 300 %m/h with the slight convex interface at the seed temperature 2250°C.