What defines a semiconductor?

A semiconductor is defined as a material that exhibits electrical conductivity between that of a conductor and an insulator. This unique property allows semiconductors to control electrical current in various applications, including transistors and diodes, which are fundamental components in electronic devices.

Semiconductors have a band gap that allows them to be conductive under certain conditions, such as the addition of impurities (doping) or changes in temperature. This property makes them extremely useful for electronic applications, where precise control of electrical flow is required. For instance, in a pure state, silicon, a common semiconductor, behaves more like an insulator, but when doped with certain materials, it can conduct electricity effectively.

In contrast, materials that are perfect conductors allow electrical flow without resistance, while perfect insulators do not allow any electrical current to flow at all. A material that emits light when heated describes a different characteristic, typically related to thermoluminescence or incandescent behavior, rather than the defining features of a semiconductor. Thus, the correct definition focuses on the intermediate conductivity of semiconductors, making option C the accurate answer.