Material characterization, patterning and adsorbate induced modulation of light emission of porous silicon produced by metal-assisted electroless etching

Metal-assisted electroless etching of Pt-patterned Si in HF, H2 O2 and methanol produces photoluminescent porous silicon (PSi). Upon ultraviolet excitation, the peak emission wavelength of PSi can be tuned in the visible spectral range simply by varying the etching conditions. Photoluminescence measurements reveal the spectral and spatial characteristics of the light emission as a function of processing parameters, while scanning electron microscopy reveals nanocrystalline features in the region where the luminescence originates. Raman scattering measurements of the shift and broadening of the longitudinal optical phonon band, interpreted in the context of the phonon confinement model, are used to estimate crystallite sizes in an attempt to correlate evolution of morphology with light emission. The results point to proximity to a deposited metal feature as a determining factor in the development of the morphology and light emission characteristics. Based on these observations, creation of photoluminescent pixel arrays in the micron and sub-micron dimension is explored by coupling of small area Pt deposition with metal-assisted electroless etching. Electroless etching produces photoluminescent PSi pixel arrays with high fidelity transfer of the Pt pattern obtained by focused ion beam assisted deposition from an organometallic precursor, trimethylmethylcyclopentadienyl platinum. The morphologies of the etched structure obtained are an admixture of porous areas coexisting with deeper heavily etched crater regions. Correlation of the morphology with the luminescence characteristics reveals that only the porous areas emit while the deeper crater areas remain dark. Development of such patterning protocols in addition to the ease of fabrication and large internal surface make PSi produced by metal-assisted electroless etching, attractive for sensing applications. However, understanding of the material behavior in different media is necessary prior to successful implementation of such interests. With this goal, a study of the chemistry and photoluminescence behavior of PSi in aqueous solutions of ionic surfactants is undertaken by photoluminescence and Fourier Transform Infrared (FTIR) spectroscopy. Modulation of the light emission of PSi in surfactant solutions can be interpreted by changes in the depletion region of the semiconductor as a result of adsorption of cationic and anionic surfactants.