Defect Characterization in 4H Silicon Carbide Bulk Crystals and Epilayers.

摘要

4H silicon carbide (4H-SiC) has been accepted as an optimal semiconductor that can substitute for silicon for fabricating advanced power devices for high temperature, high power, and high frequency applications, owing to its outstanding properties such as wide bandgap, high breakdown electric field, high saturation drift velocity and high thermal conductivity. Developments in advanced growth techniques for both 4H-SiC bulk crystals and epilayers have led to an era of large wafer sizes and relatively low defect densities, and these achievements are partly attributed to extensive and careful studies of different kinds of defects in this material. In turn, high crystal quality provides a unique opportunity to better understand defects behavior and also discover any new types of defects.;The central focus of this dissertation is to study the nature of various defects in 4H-SiC, determine their origins, and explain their formation mechanisms and the goal is to enlighten potential strategies to eventually eliminate these defects. Synchrotron x-ray topography, high resolution transmission electron microscopy, chemical etching and computer simulations have been intensively used in the studies.;The outcomes can be divided into four parts: (I) Threading c+a dislocations have been recognized from those traditionally considered as threading screw dislocations, and their nucleation, propagation and mutual interactions have been studied; (II)The defect evolution process from threading dislocations with c-component of Burgers vector to stacking faults has been studied. Deflection of threading c+a dislocations was observed to be able to create stacking faults comprising mixtures of Shockley component and Frank component. Moreover, open-core threading screw dislocations, or micropipes, were found to be the source of stacking faults with a peculiar configuration of six-pointed star shape; (III) 2D nucleation mechanisms were provided to explain the formation of stacking faults with 6H structure in the substrate and the formation of so-called V-shaped defects in the epilayer; (IV) A new method has been developed to determine the faults vectors associated with stacking faults in 4H-SiC from their stacking sequences and meanwhile to provide possible pathways to transform the perfect stacking sequence to the faulted one. This technique is also expected to be applicable to all structures comprising corner shared tetrahedra, such as 2H, 3C, 6H, and 15R.