Boron Diffusion in Intrinsic, n-Type and p-Type 4H-SiC

The diffusion of boron in 4H-SiC has been studied by secondary ion mass spectrometry. Three kinds of epitaxial layers have been used, highly p-type, highly n-type and low doped n-type (intrinsic). A boron diffusion source has been introduced in the samples by ion implantation. Subsequent anneals have been carried out in Ar atmosphere in a RF-heated furnace between 1220 deg C and 2000 deg C for 5 min to 3 h. For the boron diffusion in the highly p-doped layer, 4x1019 Al atoms/cm3, an activation energy of 5.3 eV has been determined. A similar activation energy has been extracted in the highly n-doped layer, 1x1019 N atoms/cm3, although the absolute diffusivity values differ by four orders of magnitude. In the lightly n-doped layer, transient enhanced boron diffusion is observed at intrinsic conditions.