Junction Capacitance; Bandwidth And Response - THORLABS DET100A User Manual

Si Biased Detector
The table below gives some advantages to each common type of detector
material.
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
have a profound impact on the bandwidth and the response of a photodiode. It
should be noted that larger diode areas encompass a greater junction volume
with increased charge capacity. In a reverse bias application, the depletion width
of the junction is increased, 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 and the load
r
resistance (R
LOAD
1
Approximate values, actual wavelength values will vary from unit to unit.
Page 7
) is an important property of a photodiode as this can
J
):
Dark
Current Speed
Low High
High Low
Low High
Low High
High High
1
=
(2 ×
0.35
=
1
Sensitivity
(nm)
400 – 1000
900 – 1600
150 – 550
800 – 1800
1200 – 2600
) and the rise time
BW
)
Rev F, December 8, 2014
Cost
Low
Low
Med
Med
High