What is the principle behind semiconductor materials?

Semiconductor materials are characterized by their electrical conductivity that falls between that of conductors and insulators. This unique property is a result of their atomic structure and the behavior of electrons within them.

In semiconductors, conductivity can be significantly altered by the addition of impurities, known as doping, which introduces additional energy levels within their band gap. This allows for the control of electron flow and thus conductivity by applying electric fields, heat, or light.

The other options do not accurately define semiconductors. Conductors have high conductivity, while insulators have very low conductivity. Purely insulators would not possess the ability to conduct any electricity, which does not reflect the behavior of semiconductors. Similarly, while temperature can influence semiconductor conductivity, they are not restricted to conducting electricity only under high temperatures. Instead, various temperatures can lead to varying degrees of conductivity in semiconductors, enhancing their versatility in applications such as diodes and transistors.