C-Si surface passivation by aluminum oxide studied with electron energy loss spectroscopy

In this work the mechanism of c-Si surface passivation by Al
₂
O
₃
films is studied in detail by means of spatially resolved electron energy loss spectroscopy (EELS). The bonding configuration of Al and O is studied in as-deposited and annealed Al
₂
O
₃
films grown on c-Si substrates by plasma-assisted and thermal atomic layer deposition (ALD). The ratio of tetrahedrally and octahedrally coordinated Al is found to increase after annealing, especially for the plasmaassisted ALD sample. The increase is strongest close to the c-Si/Al
₂
O
₃
interface and thus these results strongly support tetrahedrally coordinated Al as the origin for the negative fixed charge in Al
₂
O
₃
.