PROPERTIES OF SILICON-ELECTROLYTE JUNCTIONS AND THEIR APPLICATION TO SILICON CHARACTERIZATION

A number of interesting and still not fully understood phenomena occur if silicon is used as an electrode in an electrochemical cell. Effects include porous silicon layer (PSL) formation with features on a nanometer scale, surface roughening on a micrometer scale, quantum efficiencies for light generated currents much larger than 1, preferential etching of defects, electropolishing, and voltage or current oscillations. It is shown that despite the complexities of chemical reactions involved, a basic understanding of the electrode behavior is possible from a semiconductor physics point of view and that it can be advantageous to use the silicon - electrolyte junction for analytical purposes. Topics such as defect characterization, measurements of minority carrier diffusion length, or surface recombination velocities can be addressed in unique ways by taking advantage of particular properties of the silicon - hydrofluoric acid system. Based on the general description of the Si - electrolyte junction given in this paper, strengths and limitations of some electrochemical methods are discussed in some detail and illustrated by examples.