Photodiode

PhotodiodeIt is a reverse biased Si or Ge pn junction diode in which the reverse current increases when the junction is exposed to light

Reverse Bias OperationWhen no incident light, the reverse current I is almost negligible & is called Dark Current

Photodiode Operation

Operating Principle of PN Photodiode

Reverse Current Vs Irradiance

Reverse voltage Vs Reverse Currentcurve

Application of PhotodiodeAlarm Circuit using Photodiode

Application of PhotodiodeCounter Circuit using photodiode

Types of PhotodiodePN PhotodiodePIN PhotodiodeAvalanche Photodiode

PIN PhotodiodeIt is a 3 region reverse biased junction diodeUsed for the detection of light at the receiving end in optical communication.

Avalanche Photodiode (APD)It is operated under a large reverse bias condition where the electron-hole pairs generated by an optical illumination incident on the device can go through the avalanche multiplication processIt is highly sensitivity, high speed semiconductor light sensorUseful in fibre optic communication systems

Avalanche Photodiode (APD)

Medical Application of PhotodiodesPhoto diodes are used in a broad range of biomedical instruments:Pulse oximetersFinger-tip heart sensorsSingle drop blood glucose metersFiber-optic based spectrophotometersSpectrophotometric detection of tumors using endoscopesCT Scanners X ray detectionBlood Particle Analyzers

ILLUSTRATION of PULSE OXIMETER

ReferenceElectronic Devices by FloydElectronic Devices & Circuits by S Salivahanan

When light is incident on the pn junction of the photodiode, there is a transfer of energy from the incident light (photons) to the atoms in the junction, this will create more electron hole pairs. These additional free electrons will increase the reverse current.*The amount of light intensity is expressed as irradiance (mW/cm2 )*