Structure dependent ultrafast relaxation time of photo-excited carriers in SiC

The ultrafast inter-conduction band carrier dynamics in 6H-SiC and 4H-SiC was observed by using the pump and probe transient absorption technique. The observed decay times of transmission changes are 1.25 ps for 6H-SiC and 630 fs for 4H-SiC, respectively. Dependence of the transmission change on probe wavelength and polarization were analyzed by using the steady-state absorption profiles. From this analysis, the transmission change was ascribed to the decrease of electron population in the lowest conduction band. The experimental results show that the decay of the transmission change was dominated by the inter-band electron phonon scattering. The inter-band deformation potential in 4H-SiC, deduced from the observed decay time, was 1.25 times larger than that in 6H-SiC. This polytype dependence of inter-band deformation potential is discussed in terms of the hexagonality and band-gap energies.