4H to 3C Polytypic Transformation in Al+ Implanted SiC during High Temperature Annealing

다국어 초록 (Multilingual Abstract)

Polytypism in SiC has created interest and opportunity for device heterostructures and bandgap engineering in power electronicapplications. As each SiC polytype possesses a diff erent bandgap, electron mobility, and degree of anisotropy, unique interfacescan be created without changing its chemical composition. The 4H polytype is commonly used, but the 3C polytype off ers highsurface electron mobility with isotropic properties as the only cubic polytype. This has driven research on heteroepitaxy with limitedsuccess in traditional chemical vapor deposition chambers. Discussion on polytype control and stability has been restrictedto bulk and epitaxial crystal growth, despite numerous reports of polytypic transformations occurring during other processingsteps. This study revealed the polytypic transformation of 4H-SiC to 3C-SiC after high temperature annealing using high resolutioncross-sectional transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). Above1750 °C, the surface signifi cantly roughened under a reduced pressure of Ar, whereas surface planarity was maintained underAr atmospheric pressure. The formation of 3C-SiC islands occurred adjacent to large surface pits through an epitaxial growthprocess for the reduced pressure condition only. Loss of SiC stoichiometry at the surface with Si enrichment and availability ofon-axis terraces enabled 3C nucleation. 3C-SiC growth was retarded using a protective carbon cap (C-cap) where defect-freesingle crystal 3C-SiC has a coherent interface with the 4H-SiC substrate underneath. These fi ndings demonstrate that the 3Cpolytype can be stable at high temperatures, encouraging the need for a better understanding of polytype stability and control.