Which material has conductivity between a conductor and an insulator?

• A. Conductor
• B. Semimetal
• C. Dielectric
• D. Semiconductor

Answer: (D)

Conductivity spans a wide range, and semiconductors sit between metals and insulators. Metals have lots of free electrons, so they conduct very well. Insulators have a large energy gap that keeps electrons from moving, so they conduct very poorly. A semiconductor has a modest band gap, so it conductors at a moderate, tunable level. Its conductivity can be increased or decreased by changing temperature, adding impurities (doping), or exposing it to light or electric fields. That tunability is what makes semiconductors the in-between material you’re looking for. Dielectrics are essentially insulating materials used for storing charge, so they don’t sit between metals and insulators in the same way; semimetals are a different category with their own distinct behavior and aren’t the standard intermediate between conductors and insulators.