In general, semiconductors are materials, inorganic or organic, which have the ability to control their conduction depending on chemical structure, temperature, illumination, and presence of dopants. The name semiconductor comes from the fact that these materials have an electrical conductivity between that of a metal, like copper, gold, etc. and an insulator, such as glass. They have an energy gap less than 4eV (about 1eV). In solid-state physics, this energy gap or band gap is an energy range between valence band and conduction band where electron states are forbidden. In contrast to conductors, electrons in a semiconductor must obtain energy (e.g. from ionizing radiation) to cross the band gap and to reach the conduction band. Properties of semiconductors are determined by the energy gap between valence and conduction bands.
CdTe and CdZnTe as Semiconductor
Cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) have been regarded as promising semiconductor materials for hard X-ray and gamma ray detection. The high atomic number and the high density of these materials mean they can effectively attenuate X-rays and gamma rays with energies of greater than 20 keV that traditional silicon-based sensors are unable to detect. This significantly increases their quantum efficiency in comparison with silicon-based . The large band-gap energy (Egap= 1.44 eV) allows us to operate the detector at room temperature. On the other hand, a considerable amount of charge loss in these detectors produces a reduced energy resolution.