Halbleiter

Materials are broadly categorized into three types as metals, insulators, and semiconductors.

Metals have no energy band gap due to the overlap of the valence and conduction bands. This allows free electron movement, making metals excellent conductors of electricity.

In contrast, insulators have a large energy band gap, typically greater than 3 eV. At ambient temperature, no conduction occurs because the thermal energy or applied electric field is insufficient to promote a significant number of electrons from the valence band to the conduction band, making them poor conductors.

Conventional semiconductors like silicon exhibit a narrow energy band gap around 1.1 eV. At ambient temperature, a significant number of electrons can be thermally excited from the valence band to the conduction band, resulting in a small current.

This transition generates carriers. Free electrons act as carriers in the conduction band, while the voids created by the absence of electrons, known as holes, act as carriers in the valence band.

Semiconductors exhibit moderate conductivity, influenced by factors such as temperature, light illumination, and doping impurities.