Both are enumerated within heading 381800, but at separate 10-digit lines: polycrystalline silicon wafers doped for electronics at 3818000020, and silicon carbide wafers doped for electronics at 3818000030. The distinction matters because SiC is a compound semiconductor (not elemental silicon), and its classification as a 'chemical compound doped for use in electronics' is explicitly covered by the heading's scope. Importers should confirm the substrate material and doping status with the supplier's technical documentation.

CBP expects evidence that the material is intentionally doped — meaning a controlled impurity has been introduced to modify electrical properties — and that it is in a form (disc, wafer, or similar) consistent with electronic end-use. Supplier certificates of conformance specifying dopant type (e.g., boron, phosphorus, nitrogen), resistivity range, and crystal orientation are standard supporting documents. Undoped semiconductor-grade silicon or other elements may fall under different headings in Chapter 28, so doping status is the critical classification threshold.