Hydrogen-related photoluminescent centers in SiC

Local density functional calculations are used to investigate models of the center responsible for a prominent set of luminescent lines with zero-phonon lines around 3.15 eV in hydrogen rich 4H-SiC and previously attributed to VSi-H. We find that the electronic structure of this defect and the character of its vibrational modes are inconsistent with this assignment. In contrast, a H2 * center, bound to a carbon anti-site, is more stable than the isolated molecule and possesses a donor level close to that observed for the H-lines. Moreover, its vibrational modes are in good agreement with experiment. A possible mechanism for the radiation enhanced quenching of the defect is discussed.