Direct Observation of Individual Nanometer-Sized Light-Emitting Structures on Porous Silicon Surfaces

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Abstract
We present the first observations of nanometer resolution mapping of visible-light emission from 85% porous silicon. Using an STM tip as a local source of electrons to excite cathodoluminescence, simultaneous topographic and light intensity profiles are reported. The photon maps reveal contrast in emission intensity on a scale relevant to the proposed dimensions of the luminescence process (~ 4 nm). We suggest that excitation of individual quantum confinement structures has been observed. The technique overcomes the wide disparity in length scales of the photons ((600 ÷ 900) nm) and the characteristic size of the origins of the luminescence ((1 ÷ 5) nm) which have precluded previous experimental correlations of structural and luminescent behaviour.