Appl. Phys. B doi:10.1007/s00340-011-4596-y (2011)

Near-infrared LEDs emitting at wavelengths of 1–1.7 μm are commonly made from InGaAsP in a complex double-layer heterojunction structure comprising an InGaAsP active layer and an InP carrier confinement layer. Unfortunately, InP is highly toxic and In is a rare element. Silicon, although non-toxic and ubiquitous, is indirect-bandgap semiconductor and therefore exhibits low emission efficiency. Tadashi Kawazoe and co-workers at the University of Tokyo in Japan have now fabricated a highly efficient, broadband near-infrared LED from boron-doped bulk-crystal silicon whose homojunction structure is considerably simpler than double-heterojunction designs. They fabricated their device by annealing a silicon p–n junction with a forward current while irradiating the device with near-infrared light. This process produced stimulated-emission light through a two-step phonon-assisted process triggered by the optical near-field at the inhomogeneous domain boundary of boron, thus allowing the annealing rate to be controlled in a self-organized manner. For an input electrical power of 11 W, the device achieved an external power conversion efficiency of 1.3%, an external quantum efficiency of 15% and a total optical power of 1.1 W.