Defect formation and annealing in as-grown and electron-irradiated 6H-SiC wafers

were investigated using variable-energy slow positron beams. For the n-type asgrown

samples, it was found that annealing decreased the defect concentration due

to recombination with interstitials, and when it was annealed (1400C, 0.5h, vacuum), a 20nm-thick Si layer was found on top of the SiC substrate, which was a

direct proof of the Si atom diffusing to the surface when annealed at the high

temperature stages. During the high temperature annealing stage, an obvious

surface effect was found which induced a higher S parameter close to the surface.

This may have been caused by diffusion of the Si atoms to the surface during

annealing. After 10MeV electron irradiation of n-type 6H-SiC, the positron

effective diffusion length decreased from 86.2 to 39.1nm. This showed that some

defects were created in n-type 6H-SiC. But, in p-type 6H-SiC irradiated with

10MeV electrons, the change was very small. This may have been because of the

opposite charge of the vacancy defects. The same annealing behaviour as that of

as-grown 6H-SiC samples was also observed for 1.8MeV electron-irradiated 6HSiC

samples; except that, after being annealed at 300C, the defect concentration

increased. This could be explained by the generation of carbon vacancies, due

either to recombination between divacancies and silicon interstitials, or the charge

of the charge states.

Defect Characterization of 6H-SiC Studied by Slow Positron Beam. H.Y.Wang,

H.M.Weng, X.Y.Zhou: Chinese Journal of Chemical Physics, 2008, 21[4], 333-8