Historically, semiconductor detectors were conceived as solid-state ionization chambers. To obtain a high-electric-field, low-current, solid-state device for detection and possibly spectroscopy of ionizing radiation, conduction counters (highly insulating diamond crystals) were first used. However, such crystals were quickly rejected because of poor charge collection characteristics resulting from the deep trapping centers in their bandgap. After the highly successful development of silicon (Si) and germanium (Ge) single crystals for transistor technologies, the conduction-counter concept was abandoned, and silicon and germanium ionizing radiation detectors were developed by forming rectifying junctions on these materials. A semiconductor detector is a large silicon or germanium diode of the p-n or p-i-n type operated in the reverse bias mode. At a suitable operating temperature (normally ~300 K for silicon detectors and ~85 K for germanium detectors), the barrier created at the junction reduces the leakage current to acceptably low values. Thus an electric field can be applied that is sufficient to collect the charge carriers liberated by the ionizing radiation.  Some of the more useful basic concepts are summarized in the following sections.

Creation of Electron-Hole Pairs in Semiconductor Detectors by Ionizing Radiation