Charge Exchange Mechanism Responsible for P-Type Silicon Dissolution during Porous Silicon Formation

The anodic current-voltage characteristics of P sil icon which are obtained in HF electrolyte in the condit ions corre-sponding to porous layer formation are studied in detail and analyzed according to an elementary model which accounts for the deplet ion layer at the sil icon surface and the Helmholtz layer in the electrolyte. It is found that the determining step of si l icon dissolution is the charge exchange from the bulk sil icon to the semiconductor surface. This process occurs through a thermionic emission mechanism over the Schottky barrier which is formed at the sil icon surface, whenever the doping level is from 2 • 1015 to 1019 cm 3. Variations in the sil icon doping concentrat ion NA provoke a potential shift in the current-voltage characteristics, which is almost proportional to the square root of NA, and which explains the selectivity o