Hydrogen diffusion and ion implantation in silicon carbide

Sammanfattning: Secondary ion mass spectrometry (SIMS) has been employed tostudy the spatial distributions resulting from mass transportby diffusion and ion implantation in single crystal siliconcarbide (SiC). By a systematic analysis of this data,fundamental processes that govern these phenomena have beenderived.The acceptor atoms Al and B are known to be electricallypassivated by H in SiC. By studying the thermally stimulatedredistribution of implanted deuterium (2H) in various acceptordoped structures, it is found that hydrogen forms complexeswith the doping atoms, and also interacts strongly withimplantation induced defects. A comprehensive understanding ofthe formation and dissociation kinetics of these complexes hasbeen obtained. The extracted effective capture radius for theformation of 2H-B complexes is in good agreement with thatexpected for a coulomb force assisted trapping mechanism. Thelarge difference of 0.9 eV in the extracted dissociationenergies for the 2H-Al and 2H-B complexes suggests that theatomic configurations of the two complexes are significantlydifferent. Furthermore, by studying the migration behavior of Hin the presence of built-in electric fields, it is concludedthat all of the mobile H is in the positive charge state inp-type SiC.A large number of implantations have been performed withrespect to ion mass, energy, fluence, and crystal orientation.The electronic stopping cross sections in the low velocityregime for ions with atomic numbers 1 ? Z1 ? 15have been extracted from the ion range distributions. Theydisplay both Z1-oscillations and a smaller than velocityproportional stopping for ions with Z1 ? 8, in agreementwith previous reports for other materials. Furthermore, thedegree of ion channeling in various major axial and planarchannels of the 6H and 4H-SiC crystal has been explored. Twotypes of ion implantation simulators have been developed. Onebased on a statistical, data-base approach, and one atomisticsimulator, based on the binary collision approximation (BCA).By fitting BCA simulated profiles to the experimental profiles,detailed information about the electronic stopping andimplantation induced damage is extracted. In addition, thevacancy-related damage caused by the implantations has beeninvestigated by positron annihilation spectroscopy (PAS). Twotypes of implantation induced positron traps have been isolatedand are tentatively identified as a Si vacancy (VSi) and a Si-Cdivacancy (VSiVC). The extension of detected VSi is in goodagreement with that predicted by BCA simulations, and forimplantations with heavier ions VSi are revealed at far greaterdepths than the mean projected ion range due to deeplypenetrating channeled ions.