Surface Modification Of 6H-SiC Under Vacuum Annealing Studied By Time Of Flight Positron Annihilation Induced Auger Electron Spectroscopy

Abstract

This thesis presents the first study of vacuum annealing of 6H- SiC surface using Time-of-Flight-Positron Annihilation induced Auger Electron Spectroscopy(TOF-PAES) . The study was the first application of a TOF-PAES spectrometer to the SiC. The increased efficiency of the TOF-PAES allows us to see simultaneously for the first time Si-LVV, C-KVV, O-KVV peaks in the PAES spectrum for SiC. The top layer surface concentrations of C, O and Si were monitored by TOF-PAES surface. The results indicate that the SiC surface was initially covered with a layer containing oxygen but largely devoid of Si which was subsequently removed as a result of vacuum annealing to expose Si and C in the top layer. These results clearly demonstrate the utility of PAES in the study of the surface modification of SiC. In addition, the reduced secondary background associated with PAES made it possible to observe, for the first time, low energy Auger transitions from SiC at 37eV, and 53 eV. In order to confirm the reliability and efficiency of the T-O-F PAES spectrometer in measuring Auger peaks at such low energies, TOF-PAES was used to measure previously observed low energy Auger transitions in Au. The increased efficiency of the T-O-F PAES permitted us to make the first measurement of the individual low energy peaks ( 37ev, 56eV, 71 eV) in Au demonstrated the sensitivity of the spectrometer to the low energy auger electrons. This data was used to make the first experimental estimates of the relative annihilation probabilities of positron with 5d, 4f, and 5s core electrons which when compared with the theoretical values reveal a partial failure of the theory to account for the relative annihilation probabilities of electrons in the 5s level.