Optical properties of vanadium and nitrogen doped 4H and 6H-SiC

Linear optical properties of vanadium (V) and nitrogen (N) doped single-crystal sub-millimeter wafers of 4H-SiC and 6H-SiC grown for industrial applications in optics and electronics are studied in detail within transparency window and from 0.2 THz to 2.1 THz range to reveal usability in parametric frequency conversion. Manufactured wafers are found not uniform in polytype composition. Optical properties of majority of wafers indicated applicability for THz wave generation by optical rectification method. The wafers demonstrated large optical damage threshold exceeding that for widely used crystals GaSe at least for from 3 to 5 times and up to 10 times lower (from a few tens to below 1 cm⁻¹) absorption coefficient in the THz range. Birefringence of doped 4H-SiC are still close to that for pure crystals, i.e. suitable for phase matched frequency conversion within the transparency window or into the THz region. Polytype 6H seems suitable for phase matched down-conversion into the THz range. Nevertheless, absolute values of refractive indices are seriously varying wafer to wafer.