Photoelectrochemical and Nanogravimetric Study of Electrolytic Transformation of Silicon-Oxide Interface

Abstract

While silica is chemically stable in most acid electrolytes, its properties could significantly change due to electrolyte absorption. We demonstrate the photoelectrochemical and nanogravimetric features that allow identification of electrolytic transformation of Si-SiO2 interface. To that end, photoresponsivity of p-type silicon with ultrathin thermal oxide layer (10 nm) was studied. The responses were compared with those of hydrogen-terminated Si surface. The quartz crystal nanogravimetry (QCN) characterized the transformation process with nanogram resolution in situ and in real time. In neutral solution (pH 7), electrolyte absorption along with some dissolution of the silica layer has been detected by the QCN. No silica dissolution indications were observed in an acid electrolyte; its absorption was about one third of the dry oxide mass. Other discussed phenomena included photoelectron generation, recombination, and charging of the oxide film. The observed effects could be generalized to other Si/oxide systems and this has been demonstrated with HfO2 and Al2O3 ultrathin layers produced by the atomic layer deposition (ALD). The obtained results enable us to properly understand photoresponsivity, passivity, and degradation of Si/oxide electrodes for applications in devices of solar energy conversion.