In November 1962, Robert Hall and his team from General Electric reported an infrared-emitting diode made from gallium arsenide. One month later, Nick Holonyak and Sam Bevacqua, also of GE, reported a red light-emitting diode made from GaAs alloyed with phosphorus. And so began the quest to widen the application of LEDs by shortening their wavelengths.
The record now stands at 210 nm. Yoshitaka Taniyasu of NTT in Atsugi, Japan, has made the first LED that emits in the far UV. Based on aluminum nitride, the NTT LED is about a million times dimmer than its commercial, longer-wavelength counterparts. But if its output could be improved, the device could serve as a compact germicide or photolyser of harmful chemicals.
LEDs are simple devices. In essence, two slabs of semiconductor, one p-doped, the other n-doped, abut each other. Applying voltage across the slabs, from p to n, drives the extra electrons...
