DETERMINATION OF THE SPECIFIC SURFACE-AREA OF POROUS SILICON FROM ITSETCH RATE IN HF SOLUTIONS

The chemical dissolution of porous silicon (PS) layers hydrofluoric (H F) acid solutions of various compositions has been investigated. It is shown that it is possible to determine the specific surface area of P S from comparison of bulk Si and PS etch rates. We have used this new technique to characterize PS layers obtained from lightly doped p-type Si. It is shown, for the first time, that the specific surface area s ignificanfly decreases when the porosity of the material increases. Th is surface area decrease is discussed in relation to the photoluminesc ence (PL) properties of the porous layer. Furthermore, the etch rate o f PS, which increases with decreasing HF concentration, is found to co rrelate more with the pH of the solution rather than the HF concentrat ion.