Macropore formation on p-type silicon

Electrochemical anodisation of p-silicon of different crystal orientations and doping densities has been investigated in acetonitrile, propylene carbo nate and dimethylformamide solutions containing hydrofluoric acid. The form ation of a macroporous layer in acetonitrile and propylene carbonate is obs erved only if the resistivity of the silicon exceeds similar to 10 Omega . cm for both (1 0 0) and (1 1 1) crystal orientations whereas in dimethylfor mamide the macroporous layer can be formed on similar to 1 Omega . cm subst rates. The influence of water concentration in the electrolyte on the morph ology of the macroporous layer has also been studied. The resistivity of th e used electrolyte solutions was measured and compared to that of silicon. Formation of a macroporous layer is explained by the effective collection o f holes at the tip of the growing macropores.