Photodiodes

Photodiodes are a two-electrode, radiation-sensitive junction formed in a semiconductor material in which the reverse current varies with illumination. Photodiodes are used for the detection of optical power and for the conversion of optical power to electrical power. Photodiodes can be PN, PIN, or avalanche.  PN photodiodes feature a two-electrode, radiation-sensitive PN junction formed in a semiconductor material in which the reverse current varies with illumination.  PIN photodiodes are  diodes with a large intrinsic region sandwiched between P-doped and N-doped semiconducting regions.  Photons absorbed in this region create electron-hole pairs that are then separated by an electric field, thus generating an electric current in a load circuit.  Avalanche photodiodes are devices that utilize avalanche multiplication of photocurrent by means of hole-electrons created by absorbed photons. When the device's reverse-bias voltage nears breakdown level, the hole-electron pairs collide with ions to create additional hole-electron pairs, thus achieving a signal gain.