Deposition under ultra high vacuum conditions (UHV-Laboratory)

The purpose of the UHV preparation tool is 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 with TCO/a-Si:H/c-Si structure are to be investigated.

The preparation starts with oxide free, reconstructed (1000 °C in UHV) surfaces of 2 inch silicon wafers. At a base pressure of 5 10^-11mbar, solids are evaporated by means of effusion cells, electron beam evaporators or atom/radical sources. The obtained atoms and ions are then used for the materials deposition on the 2 inch silicon wafers. The ECR atom/radical source is particularly well suited for the introduction of different gases into the layers growth. Thus, it is possible to grow oxides, nitrides and also carbides under UHV base pressure conditions and, therefore, it is possible to deposit ultra thin (2-5ML) buffer layers (SiO, SiN, InN) or hetero emitters (In2O3, SiC). The substrate surface and the growth can be monitored in situ with RHEED. The analytic in situ method allows for the characterization of band offsets (constant final state yield spectroscopy, CFSYS), the electronic structure, and chemical bonding (X-ray photo spectroscopy, XPS, ultra violet photo spectroscopy UPS). A complete in situ preparation of hetero solar cells with subsequent in-situ metalization (Pt, Au, Al) is possible.

Deposited structures:

Au/Si, CoSi₂/Si, Au/CaF₂-Pufferlayer/Si, In₂O₃/SiO/Si, In₂O₃/Si