- #1
Jalo
- 120
- 0
Hi,
I'm studying p-i-n photodiode (PD) at the moment and understand that the photodiode's response will depend on the frequency of the light signal going into it. I am struggling however to understand the concept of bandwidth, and why is it that the photocurrent at the PD decreases with higher frequencies.
1. What exactly is bandwidth? My understanding it that when we launch light into the PD, it will be absorbed in the PD's depletion region, originating an electron-hole pair that will be swept across the depletion range (drift) and afterwards diffuse through the bulk semiconductor region (diffusion) until it reaches the metal contacts. If we have an oscillating light signal going into the PD, how exactly does the signal's frequency change this process, or make it less effective? Is the collection of electrons/holes less efficient at high frequencies somehow? If so, why?
2. When we talk about 3dB bandwidth, am I correct in that this is the frequency at which the photocurrent measured in the PD is half of that measured when the signal is not oscillating (0 Hz)? If so, is the process of measuring bandwidth a matter of sending first a constant signal into the PD and then simply increase the signal's frequency, keeping it's amplitude, and waiting until the photocurrent collected at the PD halves?
Apologies if the questions are a bit daft, but I've just started studying this and am struggling to get a good intuition of the PD's dependency on the light signal's frequency. Thank you very much.
I'm studying p-i-n photodiode (PD) at the moment and understand that the photodiode's response will depend on the frequency of the light signal going into it. I am struggling however to understand the concept of bandwidth, and why is it that the photocurrent at the PD decreases with higher frequencies.
1. What exactly is bandwidth? My understanding it that when we launch light into the PD, it will be absorbed in the PD's depletion region, originating an electron-hole pair that will be swept across the depletion range (drift) and afterwards diffuse through the bulk semiconductor region (diffusion) until it reaches the metal contacts. If we have an oscillating light signal going into the PD, how exactly does the signal's frequency change this process, or make it less effective? Is the collection of electrons/holes less efficient at high frequencies somehow? If so, why?
2. When we talk about 3dB bandwidth, am I correct in that this is the frequency at which the photocurrent measured in the PD is half of that measured when the signal is not oscillating (0 Hz)? If so, is the process of measuring bandwidth a matter of sending first a constant signal into the PD and then simply increase the signal's frequency, keeping it's amplitude, and waiting until the photocurrent collected at the PD halves?
Apologies if the questions are a bit daft, but I've just started studying this and am struggling to get a good intuition of the PD's dependency on the light signal's frequency. Thank you very much.