Photodiode
1. Photodiode is a photoelectric semiconductor device for detecting and often measuring radiant energy (such as light).
2. Photodiode is a two terminal electronic device which, when exposed to light the current starts flowing in the diode.
The photodiode is made up of two layers of P-type and N-type semiconductor. In this, the P-type material is formed from diffusion of the lightly doped P-type substrate. Thus, the layer of P+ ions is formed due to the diffusion process. And N-type epitaxial layer is grown on N-type substrate. The P+ diffusion layer is developed on N-type heavily doped epitaxial layer. The contacts are made up of metals to form two terminal cathode and anode.
The front area of the diode is divided into two types that are active surface and non-active surface. The non-active surface is made up of SiO2 (Silicon di Oxide) and the active surface is coated with anti-reflection material. The active surface is called so because the light rays are incident on it.
While on the non-active surface the light rays do not strike. The active layer is coated with anti-reflection material so that the light energy is not lost and the maximum of it can be converted into current. The entire unit has dimensions of the order of 2.5 mm.
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