What term describes a solid material doped with impurities to become highly conductive?

• A. Insulator
• B. Semiconductor
• C. Conductor
• D. Alloy

Answer: (B)

Doping a solid with impurities to tailor its electrical conductivity is a hallmark of semiconductors. Pure materials that are semiconductors conduct poorly on their own, but when dopants introduce extra electrons or create holes, many more charge carriers become available. This extrinsic doping dramatically increases conductivity and can be controlled precisely, which is essential for devices like diodes and transistors. An insulator remains a poor conductor even with dopants; a conductor is already highly conductive and isn’t defined by impurity-based enhancement; and an alloy is just a mixture whose conductivity is about composition in general, not the impurity-doping concept used to create semiconductors.