CATION EFFECTS ON THE ANODIC-DISSOLUTION OF N-SI IN FLUORIDE ELECTROLYTES

Under strong illumination and in the anodic range, current-potential c haracteristics of n-Si \ fluoride-electrolyte interfaces exhibit the s ame shape as those of p-Si. The increase of the photocurrent observed in the presence of alkali-metal cations of increasing size is interpre ted as for p-Si: in the electropolishing regime, cations act as cataly sts for the dissolution of the silicon-oxide layer covering the electr ode. In the dark, a negative flatband-potential shift and a decrease i n the anodic current are observed in the presence of alkali-metal cati ons of increasing size. This behaviour, which takes place on hydrogena ted surfaces, is accounted for in a kinetic model in which electrochem ical transfer takes place through negatively-charged surface states. C ation adsorption favours the presence of a negative charge at the surf ace, hence the negative charge is increased, thereby decreasing the fl atband potential and the charge-transfer rate. (C) 1998 Elsevier Scien ce S.A. All rights reserved.