The minority carrier lifetime of n-type 4H- and 6H-SiC epitaxial layers

The minority carrier lifetime has been measured on n-type 6H- and 4H-SiC epitaxial layers. We observe inherently longer lifetimes in 4H layers compared to 6H-SiC layers. A value as high as 2.1 μs has been measured 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 μs. The lifetime appears to be correlated with the morphology of the epitaxial film showing that the lifetime limiting defect may be related to a crystalline imperfection. A strong correlation can also be seen with the thickness of the epitaxial layers.