Institute Silicon Photovoltaics

Deposition at Ultra High Vacuum (UHV)

The purpose of the UHV preparation tool is to grow silicon- and metal oxide-based thin films, and to investigate the influence of surface reconstruction and few monolayer thick buffer layers on the band offset in semiconductor heterostructures. By these means the working principles, the atomic and chemical structure, and the electronic properties of efficient hetero emitter solar cells and quantum structures for solar applications can be investigated.

Film preparation usually starts with oxide free (wet-chemically etched and passivated) or reconstructed (1000°C anneal in UHV) surfaces of 2" silicon wafers. At a base pressure of ~5x10^-11 mbar solids are evaporated by means of effusion cells or electron beam evaporators. Additionally, reactive gas atoms or ions (O, N, H) are available from a RF plasma source. This allows to incorporate these species into the growing layer, to investigate reactive growth modes, and to adjust, for instance, the stoichiometry of oxidic layers either during or after growth. Furthermore, it is possible to carry out hydrogen plasma post deposition treatments.

The substrate surface and the growth can be monitored in situ with RHEED. The in situ analytical methods allow the characterization of band offsets (constant final state yield spectroscopy, CFSYS), the electronic structure (ultraviolet photoelectron spectroscopy, UPS) and chemical bonding (X-ray photoelectron spectroscopy, XPS). A subsequent in-situ metallization (Pt, Au, Al) is possible.