Applied Physics

Seeing Beneath the Surface

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Science  29 Mar 2002:
Vol. 295, Issue 5564, pp. 2329
DOI: 10.1126/science.295.5564.2329c

The presence of defects in optical-electronic materials can detrimentally affect the output efficiency of light-emitting diodes. Pinpointing the locations of defects is therefore important for characterizing semiconductor crystals and is a first step toward countering their effects or improving the synthetic process. Illuminating defects with short-wavelength light and observing the subsequent photoluminescence is the routine analytical method; however, many of the defects are buried deep below the crystal surface and out of reach of short-wavelength photons, which are absorbed in the surface region. Kawata et al. use weakly absorbed long-wavelength, or sub-bandgap, light to illuminate their semiconductor sample, but focus the beam to a sharp spot within the sample so that the defects can be excited via two-photon absorption. The ability to control where the beam is focused provides the ability to create a three-dimensional image of the defects throughout the sample. — ISO

Opt. Lett.27, 297 (2002).

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