Incident light with an energy of hv>Eg excites an electron and causes it to jump from the valence band to the conduction band, thereby creating an electron-hole (e-h) pair.

Chapter 7Optical detectors

An incident photon can cause the production of e-h pairs in three differentregions (A, B and C) in the p-n diode. However, rapid detection is only achievable in B, the depletion region.

Schematic description of field strength variations in a p-n diode. Reverse voltage and external load applied.

By applying an intrinsic layer between the p- and n-layers, the absorptionregion obtained is much broader than that of a p-n diode.

The three layers of a front-illuminated PIN diode.

PIN diode for longer wavelengths. Semiconductor materials: InP andInGaAsP.

A high reverse voltage of 100-300 V gives the electrons such high kinetic energy that multiplication of e-h pairs occurs throughcollision ionization.

Example of the distribution of field strength in an APD among the different layers.

Construction of an RAPD.

The responsivity of a photodiode is dependent both on the wavelength of the incident light and the materials used.

Model of a PIN diode with internal resistance Ri, internal capacitance Ci , and external load RL.

Relationship between BER and optical SNR.