THE MINORITY-CARRIER LIFETIME OF N-TYPE 4H-SIC AND 6H-SIC EPITAXIAL LAYERS

The minority carrier lifetime has been measured on n-type 6H- and 4H-S iC epitaxial layers. We observe inherently longer lifetimes in 4H laye rs compared to 6H-SiC layers. A value as high as 2.1 mu s has been mea sured at room temperature in 4H-SiC, however, large variations may be observed over the surface. The lifetime increases with temperature and at a typical operating temperature of a device the lifetime is close to 5 mu s. The lifetime appears to be correlated with the morphology o f the epitaxial film showing that the lifetime limiting defect may be related to a crystalline imperfection. A strong correlation can also b e seen with the thickness of the epitaxial layers. (C) 1996 American I nstitute of Physics.