Photon counting for the masses.
Last Friday on SEB someone asked about the reverse bias voltages for LEDs. So I thought I=92d try and measure it. It turned out to be very interesting. The red LEDs that I pulled out of a drawer are (I think) GaP (Newark #01H9629) from AND optoelectronics. (AND114-R) (I reported a different part number Friday, but that appears to be a mistake.) When reversed biased near 24 V they show big (~100-500mV) RC =91spikes=92 that remind me of low power ~20 Zeners. When biased just below the =91avalanche knee=92 the RC spikes are photo sensitive, with a rate that looks proportional to the light intensity. They show every indication of responding to individual photons, albeit at an extremely low efficiency. (I don=92t know of another photon counting system that can operate in room light levels.) So I=92m wondering if anyone has heard of such behavior? I tried some other leds and none show the effect. Is GaP =91special=92 in some way? If anyone wants a couple of these LEDs to look at drop me an email with name and address and I=92ll stick a few in the mail.
George H.