Defects in SiC Single Crystals and Their Influence on Device Performance

摘要

This extensive program of research aims to apply the techniques of Synchrotron White Beam X-ray Topography (SWBXT), Nomarski Optical Microscopy. Scanning Electron Microscopy. Transmission Electron Microscopy (TEM). and I-V characteristic Probing to the detailed analysis of defect structures in SiC single Crystals of various polytypes, and to determine how these defect structures can influence the performance of various kinds of device manufactures therefrom. Results obtained so far indicate that devices without screw dislocations exhibited excellent characteristics, with no detectable leakage current prior to breakdown, a sharp breakdown I-V knee, and no visible concentration of breakdown current. In contrast, devices that contained at least one elementary screw dislocation exhibited a 5% to 35% reduction in breakdown voltage, a softer breakdown I-V knee, and visible microplasmas at the sites of the screw dislocations. In addition a new strategy for preparing defect free 3C epilayers on 4H substrates was investigated. The success of this strategy was assessed using SWBXT,and results obtained to date reveal that high quality, poytype controlled 3C could be grown. The scope of the project was modified to encompass parallel studies of the influence of defect microstructure on the performance of resonators made from single crystals of the novel piezoelectric materials Langasite, Langanite and Langatate. Early results have indicated the presence of growth striations, dislocations and precipitates. The influence of these defects on device performance is being systematically studied.