![]() Due to that electric field, electron-hole pairs move away from the junction. The depletion energy will have built-in electric field. In general, an electron will have a negative charge and holes will have a positive charge. After the electron release, free electrons and hole are produced. This results in release of electron from atom structure. When the photon enters the depletion region of diode, it hits the atom with high energy. Electron hole pairs are formed when photons of energy more than 1.1eV hits the diode. Photocurrents are produced due to generation of electron-hole pairs. Generally, when a light is made to illuminate the PN junction, covalent bonds are ionized. The following image shows the symbol of a photodiode. The symbol of the photodiode is similar to that of an LED but the arrows point inwards as opposed to outwards in the LED. The smaller terminal acts as cathode and longer terminal acts as anode. Few photo diodes will look like Light Emitting Diode (LED). When surface area of photodiode increases, it results in less response time. Internally, a photodiode has optical filters, built in lens and a surface area. Typical photodiode materials are Silicon, Germanium, Indium Gallium Arsenide Phosphide and Indium gallium arsenide. Photodiode operates in reverse bias condition i.e., the p – side of the photodiode is connected with negative terminal of battery (or the power supply) and n – side to the positive terminal of battery. It is also called as Photodetector, Photo Sensor or Light Detector. The photo diode accepts light energy as input to generate electric current. ![]() Between the p (positive) and n (negative) layers, an intrinsic layer is present. Photodiode is a type of semi conducting device with PN junction. It is a form of light sensor that converts light energy into electrical energy (voltage or current). Connecting a Photodiode in an External Circuit.
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