Optically detected cyclotron resonance investigations on4Hand6HSiC: Band-structure and transport properties

We present experimental data on the band-structure and high-mobility transport properties of $6H$ and $4H-\mathrm{SiC}$ epitaxial films based on optically detected cyclotron resonance investigations. From the orientational dependence of the electron effective mass in $6H-\mathrm{SiC}$ we obtain direct evidence for the camels back nature of the conduction band between the M and L points. The broadening of the resonance signal in $4H-\mathrm{SiC}$ as a function of temperature is used to extract information on electron mobilities and to conclude on the role of the different scattering mechanisms. Under high microwave powers an enhancement of the electron effective mass is found which is explained by a coupling of the electrons with longitudinal optical phonons.