A graphite mask was used to realize selective doping of Al/B in 4H–SiC by thermal diffusion at 1800 to 2100C. The doping profiles investigated by secondary ion mass spectrometry showed that a high Al concentration of 5 x 1019/cm3 near the surface and linearly graded B profile up to several μm in depth could be obtained. Hall effect measurement was also employed to obtain the electrical characteristics of the diffused region, from which the carrier concentration (1019/cm3) and hole mobility (7cm2/Vs) at room temperature were extracted. Room temperature photoluminescence indicated that the dominant luminescence was attributed to the donor acceptor pair recombination, in which a B D complex was the prevailing center rather than Al and B shallow acceptors. Cathodoluminescence micrographs clearly illustrate a pattern with the locally diffused regions. To confirm the viability of the diffusion process, planar p-n diodes with a fairly low forward voltage drop (3.3V at 100A/cm2) and high reverse blocking capability (more than 1100V) were fabricated. Built-in voltage of 2.9V, which was typical for 4H–SiC p-n diodes, was obtained by capacitance–voltage measurement.

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