InN films were grown on Si (111) substrates by radio-frequency plasma-excited molecular beam epitaxy. InN films highly oriented to the c-axis were obtained by optimizing growth conditions in the direct growth on Si. Growth of single crystalline InN films was realized on Si substrates with substrate nitridation for 3 min. On the other hands, when the substrate nitridation was lasted over 30 min, obtained InN films were polycrystalline due to the amorphous SiNx layer formed on a substrate surface. We also studied the local atomic structure in the single crystalline InN film using extended X-ray absorption fine structure measurements.

The effects of (NH 4 ) 2 S x treatment on GaN and InN surfaces were investigated by X-ray photoelectron spectroscopy. It was found that native oxide layers were removed from nitride surfaces by HCl and (NH 4 ) 2 S x treatments and that S-terminated surface layers were formed. In addition, the S-terminated layer on the GaN surface was removed by H* irradiation. The usefulness of the combination of (NH 4 ) 2 S x treatment and post H* irradiation was shown.

Polycrystalline GaN with improved c-axis orientation is successfully grown on silica glass substrates by electron cyclotron resonance molecular beam epitaxy after nitridation of the substrate surface. This substrate nitridation gives rise to the formation of a silicon nitride layer, and results in a marked improvement in the uniformity of c-axis orientation and the surface morphology of subsequently grown polycrystalline GaN.

No abstract

Screen-printing aluminum is still dominantly used in the solar cell fabrication process. Ethyl cellulose is one of the main contents of screen-printing pastes that require dichloromethane for its cleaning process, a substance renowned for being extremely toxic and threatening to the human body. Developing environmental friendly aluminum pastes is essential in order to provide an alternative to the commercial pastes. In this work, new, nontoxic polyvinyl alcohol-based aluminum pastes are introduced. Polyvinyl alcohol was used as a soluble polymer that can be synthesized without saponification and that is also soluble in water. Three different pastes were developed using different recipes including many aluminum particle sizes varying from 3.0 to 45 μm, aluminum oxide with particle sizes between 35 and 50 μm, and acetic acid. Evaluation of the pastes was carried out by Scanning Electron Microscope (SEM) image analysis, sheet resistance measurements, and fabricating silicon solar cells using each paste. Solar cells with 15.6% efficiency were fabricated by nonvacuum processing on CZ-Si p-type wafers using developed aluminum pastes on the back side.