A review of terahertz detectors

Physics is the interplay of energy and matter. Energy, in the form of light, interacting with matter, principally in the solid state, underpins this topical review. The subject is developed carefully and methodically, beginning with basic definitions pertaining to terahertz detectors and terahertz radiation, then proceeding systematically to delineate characteristics of terahertz photons and terahertz detectors in more detail. In-between, the intimate connection linking terahertz sensors and terahertz sources is highlighted-an important aspect unfortunately often overlooked or ignored when terahertz detectors are discussed in isolation. At the centre of this topical review are the various physical mechanisms by which electromagnetic radiation of terahertz frequencies interacts with matter. The logic is to present first the underlying physical principles of detection before presenting the practical implementation in a specific device, rather than the other way around. A taxonomy of terahertz detectors is then proposed based on the underlying physical principles of detection. Following on from this classification, state-of-the-art terahertz detectors are surveyed and appraised; this overview constitutes the longest section of the review. Key detector parameters which inform applications are then presented and tabulated. Finally, the present state-of-the-art is anchored within the wider scientific context of historical developments and future prospects.