SPECTRAL AND STRUCTURAL FEATURES OF POROUS SILICON PREPARED BY CHEMICAL AND ELECTROCHEMICAL ETCHING PROCESSES

The surface morphology of porous silicon, produced by both chemical and electrochemical means, is studied by scanning force microscopy. Observed surface features in the macroscopic range (larger than 30 μm) include etch pits as well as rings and plateaus which are associated with hydrostatic forces during the etching process. In the microscopic regime (several hundred nanometers to a few microns) small hillocks, around 1 μm in diameter and approximately 100 nm high, dominate the surface structure. Missing hillocks are associated with nascent etch pits and etch pit growth is suggested to occur in steps by the rapid corrosive attack on a destabilized hillock. The presence and shape of the hillocks are attributed to surface strain which collapses the etched material. The strain can become so large as to lift the porous silicon from the surface, damaging the sample. The fluorescent properties of these materials is also discussed.