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Photodiodes
Planar Diffused Silicon Photodiode
Construction
Planar diffused silicon photodiodes are simply P-N junction diodes. A P-N junction can be formed by diffusing either a P-type impurity (anode), such as Boron, into a N-type bulk silicon wafer, or a N-type impurity, such as Phosphorous, into a P-type bulk silicon wafer.
Silicon is a semiconductor with a band gap energy of 1.12 eV at room temperature. This is the gap between the valence band and the conduction band.
Due to concentration gradient, the diffusion of electrons from the N-type region to the P-type region and the diffusion of holes from the P-type region to the N-type region, develops a built-in voltage across the junction. The inter-diffusion of electrons and holes between the N and P regions across the junction results in a region with no free carriers. This is the depletion region.
Protodiodes are semiconductor light sensor that generate a current or voltage when the P-N junction in the semiconductor is illuminated by light. The term photodoode can be broadly defind to include even solar batteries, but it usually refers to sensors used to detect the intensity of light. Photodiode can be classified by function and construction as follows:
Photodiode type
PN photodiode
PIN photodiode
Schottky type photodiode
APD (Avalance photodiode)
Features of photodiode
Excellent linearity with respect to incident light
Low noise
Wide spectral response
Mechanically rugged
Compact and lightweight
Long life
All of these types provide the above features and are widely used for detection of the intensity, position, color and presence of light.
