Optical characterization of 4H silicon carbide polytype by electromodulation spectroscopy

I present a study of the optical properties of 4H-SiC polytype. I have applied electroreflectance (ER) to a series of p- and n-doped 4H-SiC samples in order to study the fundamental band gap, higher transitions, and band narrowing in this polytype of silicon carbide. This is the first report of fundamental and next higher lying band gap study with the EM technique. The modulation spectrum ranges from the visible to the near ultraviolet regime. The series of samples studied have different doping concentration ranging from 1 x 1016 cm-3 to 1 x 1019 cm-3 and the epi-layer thicknesses of the samples range from ∼4mum to ∼10mum. The measurement is conducted with front contact electroreflectance (FCER). The results obtained are consistent with theoretical calculations and with reflectivity measurements. We also show experimentally that the band gap varies with doping concentration in 4H-SiC. I used a curve-fitting program and obtained critical points with the Aspnes third derivative method. These experimental measurements will help clearly to determine the fundamental direct band gap of 4H-SiC.