A graphite mask was used to achieve the selective doping of Al/B in 4H-SiC by thermal diffusion at 1800 to 2100C. The doping profiles, as investigated by using secondary ion mass spectrometry, showed that a high Al concentration (5 x 1019/cm3) near to the surface and a linearly graded B profile which was up to several μm in depth could be obtained. Hall-effect measurement was also used to determine the electrical characteristics of the diffused region; from which a carrier concentration of 1019/cm3 and a hole mobility of 7cm2/Vs at room temperature were deduced. The room-temperature photoluminescence indicated that the dominant luminescence was due to donor-acceptor pair recombination, in which a B D complex was the prevailing center rather than Al and B shallow acceptors. Cathodoluminescence micrographs clearly illustrated a pattern with locally diffused regions.

Selective Doping of 4H–SiC by Co-Diffusion of Aluminum and Boron. Y.Gao, S.I.Soloviev, T.S.Sudarshan, C.C.Tin: Journal of Applied Physics, 2001, 90[11], 5647-51