Fumihito Oka

Thin-film c-Si solar cells prepared by metal- induced crystallization

We prepared a thin-film polycrystalline silicon solar cell using metal-induced crystallization (MIC) of an amorphous silicon film and a thin Ni layer. The MIC using a 0.6-nm-thick Ni layer produced a highly activated n-type crystalline layer at a 5501C annealing temperature. The Ni concentration in the i-layer of a solar cell prepared by successively depositing i- and p-layers on an MIC n-layer using plasma-enhanced CVD was lower than 1 10 16 /cm 3 . This solar cell was highly responsive in the long-wavelength region of its quantum efficiency, indicating that the n/i interface and i-layer region near the n-layer were of high quality. r 2002 Elsevier Science B.V. All rights reserved.

Crystalline Structure of Highly Piezoelectric (K,Na)NbO3 Films Deposited by RF Magnetron Sputtering

We have previously reported (K,Na)NbO3 (KNN) films, whose piezoelectric properties are the highest reported thus far. In this study, we investigate the detailed crystalline structures of these KNN films after deposition on Pt/MgO and Pt/Ti/SiO2/Si substrates by RF magnetron sputtering. The KNN film on Pt/MgO was epitaxially grown on the Pt lower electrode with a perfect orientation in the perovskite structure. The KNN film on Pt/Ti/SiO2/Si was polycrystalline with a preferential orientation in the perovskite structure having dense columnar grains. X-ray diffraction measurements revealed that the KNN films grown on Pt/MgO and Pt/Ti/SiO2/Si were tetragonal; the lattice parameters c and a were related as c/a > 1. The KNN film on Pt/MgO had a higher c/a value than the KNN film on Pt/Ti/SiO2/Si, indicating that the former had more compressed strain. We conclude that this difference in compressed strain may contribute to the difference in piezoelectric properties of the KNN films on Pt/MgO and Pt/Ti/SiO2/Si.

Thickness-Dependent Micro-Raman Measurement of Poly-Si Films Prepared by Metal-Induced-Crystallization using a Ni Layer

Relatively thick amorphous silicon films for solar-cell applications were prepared by metal-induced-crystallization (MIC). Then, the thickness-dependent characteristics of micro-Raman spectra from a cross section of the prepared polycrystalline silicon (poly-Si) films were analyzed. It was found that Ni-induced crystallized films have a uniform composition that is 80% polycrystalline and 20% nanocrystalline. Also, the x-ray diffraction data show that a sub-mono-layer of Ni is sufficient for MIC of 6-μm-thick amorphous silicon (a-Si) films.