AUTHOR=Staišiūnas Laurynas , Kalinauskas Putinas , Juzeliūnas Eimutis , Grigucevičienė Asta , Leinartas Konstantinas , Niaura Gediminas , Stanionytė Sandra , Selskis Algirdas TITLE=Silicon Passivation by Ultrathin Hafnium Oxide Layer for Photoelectrochemical Applications JOURNAL=Frontiers in Chemistry VOLUME=Volume 10 - 2022 YEAR=2022 URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2022.859023 DOI=10.3389/fchem.2022.859023 ISSN=2296-2646 ABSTRACT=Hafnium oxide (HfO2) films on silicon (Si) have the potential for application in photovoltaic devices. However, very little is known about the photoelectrochemical and protective properties of HfO2 films on Si. In this study, ultrathin films of HfO2 in the range of 15 nm to 70 nm were deposited on p-Si and Au substrates by atomic layer deposition (ALD). The grazing incidence x-ray diffraction (GI-XRD) identified the amorphous structure of the layers. Quartz crystal nanogravimetry (QCN) with Si and Au substrates indicated dynamics of electrolyte intake into the oxide film. No indications of oxide dissolution have been observed in acid (pH 3) and alkaline (pH 12) electrolytes. Mott-Schottky plots showed that dark Si surface adjacent to Si-HfO2 interface is positively charged in acid electrolyte and negatively charged in alkaline electrolyte. The number of photoelectrons was determined to be much greater than the doping level of silicon. The cathodic photoactivity of p-Si electrode protected by HfO2 film was studied with respect to the reaction of hydrogen reduction in acid and alkaline solutions. In acid solution, the film enhanced the reduction process when compared to that on the coating free electrode. The acceleration effect was explained in terms of the prevention of silicon oxide formation whose passivating capability is higher than that of hafnia film. In alkaline electrolyte, an inhibition effect of the film was determined. Hafnia film protected in this medium Si from corrosion; however, at the same time, the film reduced electrode activity.