Research Highlights: Phonon-assisted Emission for Near-IR LEDs

Sep 7, 2011 A break-through research article in the field of highly efficient near-infrared LEDs has been recently published by Tadashi Kawazoe and co-workers from the University of Tokyo in the Applied Physiscs B (Lasers and Optics). It has also been highlighted by James Baxter in Nature Photonics.  He points out that most commonly near-infrared LEDs (emission wavelengths of 1–1.7 μm) are produced 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. The Japanese research team have now fabricated a highly efficient, broadband near-infrared LED from boron-doped bulk-crystal silicon whose homojunction structure  that 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.

Original research article is available online free of charge via Open Access:

Highlight at Nature Photonics by James Baxter:

Author:  Alice Jones

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