Minority carrier diffusion length measurements in 6H-SiC

Minority carrier diffusion lengths were measured as a function of temperature and position along the growth axis of lightly nitrogen doped boules of 6H-SiC grown by the physical vapor transport technique. It is shown that the diffusion lengths increase from 1 to 2 microns in the seed portion of the boule to about 4 microns in the tail portion of the boules. Deep levels transient spectroscopy measurements revealed the presence of deep electron traps with the activation energies of 0.35 eV, 0.5 eV, 0.65 eV, and 1 eV. The densities of all these traps decrease when moving from seed to tail of the boules. A good correlation between the change of the lifetime values and the density of the 0.65 eV and 1 eV electron traps was observed. The measured lifetimes show an increase with temperature following a power law that suggests that the hole capture could be determined by cascade capture process