Near-field optical investigation of porous silicon samples

Near-field optical spectroscopy has been used to study the photoluminescence features of a porous silicon device at room temperature, with a subwavelength space resolution of about 50-100 nm. In particular, a prototype of a porous silicon-based light-emitting diode has been characterized by imaging morphology, near-field scattering intensity and emission maps of the same portion of the sample with a space resolution of better than 60 nm. Structured emitting centres are found on the porous regions with size ranging from 200 nm to 1 mu m. Emission features, acquired as near-field spectra as well as emission maps at fixed wavelengths, provide crucial information on the prototype structure at the nanometric level, exploitable for improvement in production steps as well as for the study of the dominant working mechanisms of the device.