Has been demonstrated. Researchers at the University of Illinois at Urbana-Champaign used indium gallium phosphide and gallium arsenide to build a transistor with an infrared optical output port in addition to the conventional electrical input and output ports. Although the LET produces light in essentially the same way that light-emitting diodes operate, the transistor can modulate light at much higher speeds. Limited not by the optical recombination time but by the transistor itself, the device’s speed can be greater than its current 1 MHz. The emission, shown here under normal bipolar bias, comes from a 1-µm2 region in the base layer. (M. Feng, N. Holonyak Jr, W. Hafez, Appl. Phys. Lett. 84, 151, 2004. https://doi.org/10.1063/1.1637950 )
