Is the light emitting diode (LED) an ultimate lamp?

Simple diagrams art: used to show the transformation of a thin "slab'' of intrinsic semiconductor (direct gap, k(elec)=k(hole)) from an ideal ''flat-band" photopumped recombination-radiation light source into an ultimate lamp, a p-n junction light emitting diode (LED). A photoexcited intrinsic slab of semiconductor can be regarded as an ideal ("flat-band") light source, with, however, the photogenerated carriers and voltage available externally instead of as recombination radiation (light) if the slab is converted to half p type (one side) and half n type (the other side), i.e., to a p-n junction. If an equal, a ''bucking," external voltage is applied, resulting in an input current when the photoexcitation is removed, the slab becomes again (remains) an ideal "flat-band" light source, a p-n junction LED. In practice, the LED takes the form of a p-n heterostructure in order to improve electron-hole injection, reduce the absorption of recombination radiation, and to make possible-with proper geometries-improved photon escape. (C) 2000 American Association of Physics Teachers.