Spin-lattice relaxation in aluminum-doped semiconducting 4H and 6H polytypes of silicon carbide

摘要

NMR spin-lattice relaxation efficiency is similar at all carbon and silicon sites in aluminum-doped 4H and 6H-polytype silicon carbide samples, indicating that the valence band edge (the top of the valence band), where the holes are located in p-doped materials, has similar charge densities at all atomic sites. This is in marked contrast to nitrogen-doped samples of the same polytypes where huge site-specific differences in relaxation efficiency indicate that the conduction band edge (the bottom of the conduction band), where the mobile electrons are located in n-doped materials, has very different charge densities at the different sites. An attempt was made to observe ~(27)Al NMR signals directly, but they are too broad, due to paramagnetic line broadening, to provide useful information about aluminum doping.