Using a light-emitting diode as a high-speed, wavelength selective photodetector

A light-emitting diode (LED) can function as a wavelength selective photodetector. To evaluate the potential for a LED-based photodetector, we have investigated the stationary and temporal characteristics of two kinds of LEDs: a Zn-doped InGaN blue LED and a GaAlAs red LED. The application of a high current produced two peaks on the emission spectra of the blue LED, at 380 and 450 nm. The extinction profile of the blue LED was consistent with its UV-emission profile. The red LED showed an emission peak at 660 nm and an extinction peak at 620 nm. The LED-based photodetector responded within nanoseconds of the onset of the light impulse. The application of a reverse bias to the LED caused the time spread of the output current wave form to decrease dramatically and was accompanied by an increase in peak height. At a 75 V reverse bias, the resultant pulse widths were 2.6 ns in the blue LED and 7.4 ns in red LED.