Semiconductor device having a hetero-junction between SiC and a Group 3B-nitride

A semiconductor device comprising two adjacent semiconductor layers of different materials forming a heterojunction therebetween, a first of said layers having a larger gap between the conduction band and the valence band than a second layer, and being doped with impurities providing charge for forming a high mobility surface channel in the second layer at the interface between said first and second layers, wherein the second layer is made of SiC and the first layer is made of one of a) AlN and b) an alloy of AlN and at least one other Group 3B-nitride, wherein said first layer includes a first region closest to said junction made of AlN, and wherein said first layer includes a second region adjacent to said first AlN region and separated from said junction thereby, said second region is made of an alloy of AlN and at least one other Group 3B-nitride.