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Chapter 7
Optical detectors
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.
An incident photon can cause the production of e-h pairs in three different
regions (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 absorption
region 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 and
A high reverse voltage of 100-300 V gives the electrons such high
kinetic energy that multiplication of e-h pairs occurs through
collision 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.