Paper EM+NC-ThM11
The SiC Surface: A Surface of Growing Technological Importance

Thursday, October 23, 2008, 11:20 am, Room 210

Silicon carbide has become a highly versatile substrate providing a foundation for device technologies based on III-V nitrides, silicon carbide and graphene materials. In each of these systems, the starting silicon carbide surface plays a pivotal role in determining the properties and qualities of the material. The importance of surface orientation and preparation to each materials system will be discussed in terms of step morphology and contributions of extended defects in the substrate. For III-V nitride heteroepitaxy, basal plane SiC is preferred and surface morphology plays a critical role in the defectivity of films. Engineered SiC substrate surfaces are used to create localized regions of the surface with widely varying step densities including areas nearly free of surface steps. Experiments show that surface steps are directly responsible for extended defects in the heteroepitaxial layers. Nearly step-free surfaces are used to demonstrate drastically reduced extended defect concentrations (≤10⁷ cm^-2) in GaN epilayers. In regard to SiC homoepitaxy, the key elements are the control of polytype deposition, the removal of surface imperfections arising from the substrate, and the reduction or elimination of extended defects arising from the substrate or during the epitaxial nucleation process. Substrates are prepared oriented slightly away from the basal plane to promote single polytype epitaxy and off-cut toward <11-20> to promote the smoothest films. Although modification of the surface is an unavoidable first step to epitaxy due to the reactive nature of hydrogen at growth temperatures near 1600°C, the best epitaxy occurs when the surface is controllably etched to remove unwanted polishing damage. And with the desire to fully exploit the properties of SiC for high power devices, it is necessary to initiate the epitaxy in such a way as to greatly reduce or eliminate extended defects. In the new field of graphene formation through sublimation of SiC surfaces, key elements are the removal of surface imperfections from the substrate and the control of surface properties, i.e., steps that may be used advantageously for specialized devices. Key aspects of surface properties and preparation will be discussed in terms of surface structure and extended defect intersection with the surface as characterized by atomic force microscopy, electron channeling contrast imaging, and transmission electron microscopy.