Junction Capacitance; Bandwidth And Response - THORLABS DET Series User Manual

DET08C(/M) Biased Detector
The table below compares five common types of detector materials.
Material
Silicon (Si)
Germanium (Ge)
Gallium Phosphide (GaP)
Indium Gallium Arsenide (InGaAs)
Extended Range: Indium Gallium
Arsenide (InGaAs)
4.5.

Junction Capacitance

Junction capacitance (C
a profound impact on the photodiode's bandwidth and response. It reaffirms that
larger diode areas encompass a greater junction volume with increased charge
capacity. In a reverse bias application, the depletion width of the junction
increases; thus, effectively reducing the junction capacitance and increasing the
response speed.
4.6.

Bandwidth and Response

A load resistor will react with the photodetector junction capacitance to limit the
bandwidth. For best frequency response, a 50 Ω terminator should be used in
conjunction with a 50 Ω coaxial cable. The bandwidth (f
response (t ) can be approximated using the junction capacitance (C
r
load resistance (R
1
Approximate values, actual wavelength values will vary from unit to unit.
Page 6
) is an important property of a photodiode as it can have
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Chapter 4: Operation
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