Wet chemical passivation and characterization of silicon interfaces for solar cell applications

The interface properties of silicon solar cell structures were characterized by the two non destructive and highly surface sensitive spectroscopic techniques surface photovoltage and spectroscopic ellipsometry. The resulting charge and density of interface states as well as the microscopic surface roughness and oxide coverage were investigated during silicon wafer preparation and during sample storage in air. The surface state density of hydrogen terminated silicon surfaces as well as the long time stability of the hydrogen termination were found to primarily depend on the surface morphology resulting from the wet chemical oxidation procedures applied before. The smallest interface state densities were obtained by NH4F treatment subsequent to oxidation in ultra pure water at 80 C. Surfaces prepared using this procedure are found to be much more stable upon exposition to clean room air than those prepared by conventionally prepared H terminated surfaces. The successful application of the new passivation procedures in photovoltaics is shown for selected examples of different solar cell concept

Wet chemical preparation and spectroscopic characterization of Si interfaces

The combination of fast, nondestructive, and surface sensitive spectroscopic methods, surface photovoltage technique SPV , spectroscopic ellipsometry in the ultra violet and visible region UV VIS SE and Fourier Transform infrared ellipsometry FTIR SE provided detailed information about the influence of surface microroughness and the hydrogen and oxide coverage on electronic properties of H terminated and oxidized silicon interfaces during the wet chemical preparation process. By systematic investigations of common and newly developed wet chemical preparation methods, correlations were established between the preparation induced surface morphology, the resulting interface charge, the density and energetic distributions of interface states. It was shown that the efficiency of passivation on wet chemically treated Si 111 and Si 100 interfaces and the stability of H termination in clean room atmosphere strongly depends on the remaining surface microroughness and initial interface state densit

Optical investigations of beta FeSi2 with and without Cr addition

Thin films of b FeSi2 with Cr addition grown on Si 100 and Si 111 substrates were studied by UV VIS NIR spectroscopic ellipsometry as well as transmission and reflection measurements at room temperature. In MBE preparation part of the Fe atoms were substituted by Cr during deposition. For low Cr content in the doping range up to approximately 0.4 at a modified epitaxial growth was found on Si 111 substrates with the b FeSi2 100 grain orientation strongly preferred. Higher amounts of Cr lead to the precipitation of CrSi2 and a deterioration of film morphology. Furthermore, b FeSi2 thin films were implanted with Cr and subsequently annealed at various temperatures. In these samples also CrSi2 was detected. The results suggest that it is impossible to produce b Fe1 x,Crx Si2 alloys x gt; 0.003 with MBE or ion implantatio