The diffusion of D in B- and Al-doped 4H and 6H-SiC was studied by means of secondary ion mass spectrometry (table 1). From the 2H depth profiles, following trap-limited diffusion with negligible complex dissociation, the effective capture radius for the formation of 2H-B complexes (at 460C) was determined 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 non-negligible, the 2H diffusion obeyed Fick’s law, with a constant effective diffusivity from which the complex dissociation frequencies were determined. The resultant values of the complex dissociation frequencies covered 3 orders of magnitude and exhibited a near-perfect Arrhenius temperature dependence of both 2H-B and 2H-Al complexes. A large difference between their complex dissociation energies, 2.51eV and 1.61eV, suggested that the atomic configurations of the 2 complexes were quite different. The corresponding dissociation attempt frequencies, 1.2 x 1013/s 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 a first-order dissociation process. No difference between 4H- and 6H-SiC was observed.

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

Diffusivity of D in SiC