Photodetectors, also called photosensors, are sensors of light or other electromagnetic radiation. There are a wide variety of photodetectors which may be classified by mechanism of detection, such as photoelectric or photochemical effects, or by various performance metrics, such as spectral response. Semiconductor-based photodetectors typically use a p–n junction that converts photons into charge. The absorbed photons make electron–hole pairs in the depletion region. Photodiodes and photo transistors are a few examples of photo detectors. Solar cells convert some of the light energy absorbed into electrical energy.

Classification

Photodetectors can be classified based on their mechanism of operation and device structure. Here are the common classifications:

Based on mechanism of operation

Photodetectors may be classified by their mechanism for detection: Photodetectors may be used in different configurations. Single sensors may detect overall light levels. A 1-D array of photodetectors, as in a spectrophotometer or a Line scanner, may be used to measure the distribution of light along a line. A 2-D array of photodetectors may be used as an image sensor to form images from the pattern of light before it. A photodetector or array is typically covered by an illumination window, sometimes having an anti-reflective coating.

Based on device structure

Based on device structure, photodetectors can be classified into the following categories: These are some of the common photodetectors based on device structure. Each type has its own characteristics, advantages, and applications in various fields, including imaging, communication, sensing, and scientific research.

Properties

There are a number of performance metrics, also called figures of merit, by which photodetectors are characterized and compared

Subtypes

Grouped by mechanism, photodetectors include the following devices:

Photoemission or photoelectric

Semiconductor

Photovoltaic

Thermal

Photochemical

Polarization

Graphene/silicon photodetectors

A graphene/n-type silicon heterojunction has been demonstrated to exhibit strong rectifying behavior and high photoresponsivity. Graphene is coupled with silicon quantum dots (Si QDs) on top of bulk Si to form a hybrid photodetector. Si QDs cause an increase of the built-in potential of the graphene/Si Schottky junction while reducing the optical reflection of the photodetector. Both the electrical and optical contributions of Si QDs enable a superior performance of the photodetector.