ULTRATHIN LUMINESCENT NANOPOROUS SILICON ON N-SI - PH DEPENDENT PREPARATION IN AQUEOUS NH4F SOLUTIONS

Thin nanoporous Si layers were formed on n-Si(100) in 0.1 M NH4F elect rolyte and investigated with held emission scanning electron microscop y and photoluminescence (PL). The microstructure of the electrochemica lly prepared Si surfaces depended strongly on the pH of the electrolyt e. A pebble like surface structure was formed during anodization at pH 4.5, while nanoporous Si layers were formed at lower pH. The onset of macropore formation was observed after anodization at pH 3.0. The sha pe of the PL spectra was found to be practically independent of the na noporous structure. The results are discussed on the basis of the etch rate of oxidized Si atoms and of the role of surface states for FL. ( C) 1995 American Institute of Physics.