I am looking for a photodiode with a peak reception in the 630nm range. I really want high rejection of the 450nm band. However, this doesn't appear to be easily found, for sure not for low cost.
So my options are:
- Use long-pass filters on more standard photodiodes.
- Use an LED for a photodiode.
So the real question is: What are the drawbacks/advantages of using a standard LED for a photodiode? Speed? Reliability? Bandpass filtering? Linearity over temperature and input light intensity?
Best Answer
It's characteristic of the photoelectric effect that there is a minimum photon energy to stimulate a photocurrent, and thus a maximum wavelength detected. But there's no fundamental cut-off for shorter wavelengths. As such, you will not be likely to find a photodiode material that inherently has a strong response at 630 but a very weak response at 450 nm. This is also true if you use an LED as a photodiode.
You will likely have to introduce an optical filter of some kind into your system. This could be a coating on the photodiode surface, or on the window of the photodiode package; or it could be added somewhere in the optical path leading to the detector.