The diffusion of D in B- and Al-doped 4H- and 6H-SiC was studied by using secondary ion mass spectrometry (table 1). From the D depth-profiles, following trap-limited diffusion with negligible complex dissociation, the effective capture radius for the formation of D-B complexes at 460C was deduced to be 2.1nm. This value was in good agreement with that expected for a Coulomb-force assisted trapping mechanism. Under annealing conditions where dissociation was not negligible, the D diffusion obeyed Fick’s law with a constant effective diffusivity; from which the complex dissociation frequencies were deduced. The resultant frequencies covered 3 orders of magnitude, and exhibited a near-perfect Arrhenius temperature dependence for both D-B and D-Al complexes. The large difference between the deduced complex dissociation energies for B (2.51eV) and Al (1.61eV) suggested that the atomic configurations of the 2 complexes

were significantly different. The corresponding dissociation attempt frequencies, of 1.2 x 1013 and 7 x 1012/s, were very close to the characteristic oscillation frequency of the SiC lattice (1.6 x 1013/s). This was considered to be strong evidence for the assumption of a first-order dissociation process. No difference was observed between 4H- and 6H-SiC.

Hydrogen Diffusion, Complex Formation and Dissociation in Acceptor-Doped Silicon Carbide. M.S.Janson, A.Hallén, M.K.Linnarsson, B.G.Svensson: Physical Review B, 2001, 64[19], 195202 (12pp)

 Table 1

 Diffusion of D in SiC