Hydrogen diffusion in acceptor-doped silicon carbide: Implementation of the reaction zone concept

In the work of Janson [Phys. Rev. B 64, 195202 (2001)], an experimental study of deuterium (H2) diffusion in B- and Al-doped silicon carbide (SiC) was performed. A trap-limited diffusion model was used as a basis for analysis. Using the same model, in this paper, we introduce the concept of a dynamical reaction front, namely, a distinctive, well-defined zone, to which the reaction of the deuterium-dopant complex formation is confined. This zone lies between the already-deuterated and the non-deuterated regions and penetrates gradually into the specimen. We obtain analytical expressions for the spatial profiles of the free and complexed deuterium and for the reaction rate profiles. The analysis predicts that the reaction zone width initially remains constant as the zone progresses into the sample; yet, after a certain time, the zone starts to widen proportionally to the square root of time. We propose an alternative method of experimental analysis, where the reaction zone position and width as functions of time are measured. This should yield the same process parameters, as determined by the method of Janson [Phys. Rev. B 64, 195202 (2001)].