THORLABS DET10A, Руководство пользователя, Страница: 8 / 20

Si Biased Detector Chapter 4: Operation
Page 6 13052-D05
The table below gives some advantages to each common type of detector material.
Material
Dark
Current Speed
Sensitivity
a
(nm) Cost
Silicon (Si) Low High 400 – 1000 Low
Germanium (Ge) High Low 900 – 1600 Low
Gallium Phosphide (GaP) Low High 150 – 550 Med
Indium Gallium Arsenide
(InGaAs)
Low High 800 – 1800 Med
Extended Range: Indium
Gallium Arsenide (InGaAs)
High High 1200 – 2600 High
4.5. Junction Capacitance
Junction capacitance (C
J
) is an important property of a photodiode as this can 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
BW
) and the rise time
response (t
r
) can be approximated using the junction capacitance and the load
resistance (R
LOAD
):
1
2

0.35
a Approximate values, actual wavelength values will vary from unit to unit.