This instructable makes you understand mechanism of photodiode.

I was quickly looking my drawers to find something made of GLASS and I found Photodiode so I quickly made this instructable.

They are used in remotes, Robots and other many Fields.

I hope you would like it as this is the basics of Photodiodes for beginners.

Step 1: Materials Necessary to Understand It

1. Photodiode

2. 330 OHM Resisitor

3. 9v Battery

4. Micro Ammeter

Step 2: What They Are Made Up Of?

Photodiodes are mainly made from gallium arsenide instead of silicon because silicon creates crystal lattice vibrations called phonons when photons are absorbed in order to create electron-hole pairs.

Photodiodes senses the light and due to the semiconductor used in it. It senses the light of energy greater than

h(Plank's Constant)x c(Speed of light in vacuum) /Wavelength of light

Where,

h=6.625x10^-34

c=3x10^8

Step 3: Working

Assemble the circuit as shown in the circuit diagram.

When the light of Energy greater than the described energy in 1st step. The energy should be greater than the band gap energy of Gallium Arsenide. Band Gap energy is the the energy in eV needed to make the electrons free from valence band to conduction band. Holes are created in place of electrons which have ability to attract electrons.

Here the Photodiode is a PN Junction Diode which should be kept in reverse biased condition to sense the light. Micro ammeter is connected to check the current.

Step 4: Method of Testing

After assembling Circuit, as the light falls on the photodiode the microammeter shows deflection and as we darken the area around photodiode, the current decreases.

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