EFFECTS OF CHEMICAL SURFACE TREATMENTS ON THE GENERATION OF AC SURFACE PHOTOVOLTAGES IN P-TYPE SILICON-WAFERS

The AC surface photovoltage (SPV) is generated in p-type silicon wafers treated by aqueous hydrofluoric acid (HF) dipping and an alkaline rinse. Very soon after the HF dipping, the wafer surface is found to be strongly inverted due to a large positive charge. The observed AC SPVS in the HF dipped p-type Si wafer decrease as the time of exposure to air increases, showing a reverse S-shaped curve and inflection points which correspond to the layer by layer growth of the native oxide. The alkaline rinse generates relatively low AC SPVS, implying small positive charge on the p-type Si wafer. The AC SPVS in both cases decrease because positive fixed oxide charge decreases as the native oxide grows after the HF dipping and negative charge possibly neutralises the positive fixed oxide charge after the alkaline rinse.