What is the radiation-sensitive portion of a semiconductor detector made of?

The radiation-sensitive portion of a semiconductor detector is made of a material that can efficiently produce electron-hole pairs when it interacts with ionizing radiation. In this context, electron-emissive crystals are typically composed of semiconductors such as silicon or germanium. These materials have properties that enable them to effectively detect and measure radiation levels.

When radiation passes through the semiconductor, it deposits energy, which can excite electrons from the valence band to the conduction band, creating electron-hole pairs. This process is fundamental to the operation of semiconductor detectors, as the generated charge carriers can then be collected and measured, providing insight into the radiation's intensity and type.

Other materials listed, such as silicon dioxide, metal alloys, and liquid helium, do not possess the necessary properties for direct detection of radiation in the way that electron-emissive crystals do. Silicon dioxide, for example, is an insulator and does not generate charge carriers effectively in response to radiation, while metal alloys may not have the semiconductor properties required for this application. Liquid helium is not involved in the detection mechanism of radiation in semiconductor detectors.