Due to the wide band gap of SiC wafer, SiC does not absorb part or almost all of the visible light. The wavelength of the absorbed light depends on the band gap, the energy levels of the main impurities and the excited energy levels in the band. It is well known that carrier absorption in the conduction band exists in most SiC polytypes. For n-type 4H SiC, it occurs at 460 m (blue light), while for n-type 6h SiC wafer, it occurs at 620 nm (red light). The high purity 4H SiC and 6h SiC have wide band gap and are colorless and transparent as glass. However, n-type or p-type doping induces carrier absorption in the visible range, and its unique optical absorption and transmission characteristics endow each SiC crystal with unique color. Below table 1 summarizes the colors of the main SiC polymorphs with different doping types. As the color of SiC crystal becomes darker with the increase of dopant concentration, the color and color depth become good indicators of dopant type and concentration. The color of SiC crystal is also a good mark to identify the polymorphs of n-type materials.

Table 1: Colors of SiC Wafer in Different Polytype

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