Correlation between bulk morphology and luminescence in porous silicon investigated by pore collapse resulting from drying

We used a combination of scanning electron microscopy, laser scanning confocal microscopy and luminescence spectroscopy to correlate the emission properties of anodized porous silicon (PS) with film morphology in samples that have undergone solvent evaporation-induced collapse of the underlying porous structure. Several PS samples were investigated as a function of the current density (J) and total etch time, while the total charge (Q) injected per unit area (with the total amount of Si removed) was kept constant during etching. From these data, two classes of PS samples emerge. Porous silicon samples produced at high current density have a three-dimensional pore network with a narrow distribution of blue–green emitting chromophores. In contrast, low current density samples form a two-dimensional pore network normal to the Si substrate with larger chromophores and exhibit broad red luminescence. 2002 Elsevier Science B.V. All rights reserved.