# How to measure the bandwidth of a photodetector?

#### Durianpastry

Summary
how to measure the bandwidth of a photodetector and to calculate the shot noise?
I am new to photodetectors. I know there are usually two concepts of bandwidths of photodetectors, i.e the spectral and electrical.
What I do not understand is the electrical bandwidth.
The electrical bandwidth is used to calculate the shot noise of a photodetector. However, the papers usually don't show how to get the bandwidth.
I searched some references, and the bandwidth is related to capacitance and series resistance. So may I measure the EIS to get the capacitance and resistance to calculate the bandwidth?
Is the bandwidth used to calculate the shot noise the same with 3dB frequency?
But it seems that they are not the same?
I am so confused....
May someone tell me how to measure the electrical bandwidth of photodetectors?

Related Electrical Engineering News on Phys.org

#### DaveE

Why not just look at the datasheet for your detector, or ask the manufacturer? They have already characterized them.

Do you have an application that this is important - or is it just a general question? It would seem - given a specific application, you could derive a test based on that vs how the OEM characterized it.

#### Durianpastry

Do you have an application that this is important - or is it just a general question? It would seem - given a specific application, you could derive a test based on that vs how the OEM characterized it.
Well, it is a general question about the bandwidth.
Why not just look at the datasheet for your detector, or ask the manufacturer? They have already characterized them.
Because I fabricate one photodetector by myself and I do not know how to characterize it...

#### Tom.G

Since noise is broadband, it is typically measured at the bandwidth you will be using. This search found many descriptions and methodologies:

#### DaveE

If you apply a DC reverse bias and block all radiation from hitting the junction, then the equivalent circuit is basically a capacitor (bias dependent, of course), a small series resistance, and a large shunt resistance. You can connect this to a network analyzer (or other instruments) with appropriate DC blocks to measure the high frequency characteristics (like S11, for example) of these parasitic elements.

#### Durianpastry

If you apply a DC reverse bias and block all radiation from hitting the junction, then the equivalent circuit is basically a capacitor (bias dependent, of course), a small series resistance, and a large shunt resistance. You can connect this to a network analyzer (or other instruments) with appropriate DC blocks to measure the high frequency characteristics (like S11, for example) of these parasitic elements.
Thank you!

#### Durianpastry

Since noise is broadband, it is typically measured at the bandwidth you will be using. This search found many descriptions and methodologies:
Thank you!

"How to measure the bandwidth of a photodetector?"

### Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving