Passivation layers for electrochemical water splitting
Tandem structures based on III-V-semiconductors can be strongly effected by water, oxygen and hydrogen. This includes the chemical modification of the near surface region by chemical reactions such as oxidation but also the surface electronic structure e.g. by charge transfer processes causing surface band bending. Therefor suitable passivation layers with adjusted electronical properties which ensure long term stability at the same time are needed. Based on previous experience we will evaluate the suitability of Ga-based nitrides for this purpose. The corresponding layers will be grown by PAMBE using absorber materials provided, like quantum well InP. Afterwards these layers will be analyzed with respect to morphology, composition and electronic structure. To ensure long term stability the layers have to protect the tandem structures on one hand and to provide adjusted electronical properties on the other. These challenges will be addressed by careful analysis of the molecule surface interaction on one hand. In order to obtain a fundamental understanding of these interaction processes, careful in vacuo studies by offering selected molecules – with a clear focus on water molecules - to the neat passivation layers will be performed. On the other hand the electronic structure including the interface band alignment and surface band bending is equally important and will be analyzed for the selected structures.
For the detailed investigations, besides a (PA)MBE system with RHEED, a powerful combination of experimental methods is available including XPS, UPS, STM/AFM, AES and in near future MIES and TPD.