Photodiodes which can operate in photovoltaic mode or photoconductive mode. Photodiodes are often combined with low-noise analog electronics to convert the photocurrent into a voltage that can be digitized. Phototransistors, which act like amplifying photodiodes. Pinned photodiodes, a photodetector structure with low lag, low noise, high quantum efficiency, and low dark current, widely used in most CCD and CMOS image sensors. Quantum dot photoconductors or photodiodes, which can handle wavelengths in the visible and infrared spectral regions. Semiconductor detectors are employed in gamma and X-ray spectrometry and as particle detectors. Silicon drift detectors (SDDs) are X-ray radiation detectors used in x-ray spectrometry (EDS) and electron microscopy (EDX). Photovoltaic Photovoltaic cells or solar cells which produce a voltage and supply an electric current when sunlight or certain kinds of light shines on them. Thermal Bolometers measure the power of incident electromagnetic radiation via the heating of a material with a temperature-dependent electrical resistance. A microbolometer is a specific type of bolometer used as a detector in a thermal camera. Cryogenic detectors are sufficiently sensitive to measure the energy of single x-ray, visible and infrared photons. Pyroelectric detectors detect photons through the heat they generate and the subsequent voltage generated in pyroelectric materials. Thermopiles detect electromagnetic radiation through heat, then generating a voltage in thermocouples. Golay cells detect photons by the heat they generate in a gas-filled chamber, causing the gas to expand and deform a flexible membrane whose deflection is measured. Photochemical Photoreceptor cells in the retina detect light through, for instance, a rhodopsin photon-induced chemical cascade. Chemical detectors, such as photographic plates, in which a silver halide molecule is split into an atom of metallic silver and a halogen atom. The photographic developer causes adjacent molecules to split similarly. Polarization The photorefractive effect is used in holographic data storage. Polarization-sensitive photodetectors use optically anisotropic materials to detect photons of a desired linear 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. Frequency range In 2014 a technique for extending semiconductor-based photodetector's frequency range to