Laser deflection measurements for the determination of temperature and charge carrier distributions in 4H-SiC power diodes

A change of the electron and hole densities Δn and Δp and of the lattice temperature ΔT modulates the real optical refractive index n_opt of the device under test. In the forward conducting state the electron and hole distributions n(x) and p(x) in the i-region of the device are generated by the action of carrier injection from the n- and p-emitters. The device is locally heated by Joule and recombination heat, leading to a temperature distribution T(x). The gradients of temperature and charge carrier densities cause a spatial modulation of the real refractive index n _opt(x). A laser beam transmitted orthogonally to the direction of current flow of the device is deflected by the gradient of n_opt(x). Concurrent deflections caused simultaneously by the carrier gradients on the one side and by the temperature gradient on the other side can be discriminated by their different time constants.