Yasushi Minagawa

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.

Fabrication of -Oriented Si Film with a Ni/Ti Layer by Metal Induced Crystallization

We used metal-induced-crystallization (MIC) to crystallize amorphous silicon (a-Si) films over 1 µm thick. We employed a Ni/Ti layer for MIC. The a-Si films with the Ni/Ti layer were annealed at 550°C. We found that a 6-µm-thick Si film was oriented in the direction by inserting a Ti layer between Ni and the glass substrate. If the thicknesses of the Ni and Ti layer were nearly the same, the peak intensity ratio of the (220) to (111) planes was 3%. This oriented growth tendency is maintained from the beginning of crystallization to the full-crystallized stage.

Improvement of life time of minority carriers in GaAs epi-layer grown on Ge substrate

Abstract A buffer layer structure on Ge substrate was studied for MOCVD growth of a high-quality GaAs layer. The buffer layer structure was designed taking into consideration both lattice constants and thermal expansion coefficients of GaAs and Ge. It consisted of a preliminarily grown thin layer of Al x Ga 1− x As and a GaAs layer. Photoluminescence (PL) decay of a GaAs layer in an Alo 0.2 Ga 0.8 As-GaAs-Al 0.2 Ga 0.8 As double-hetero (DH) structure, which was grown on the buffer layer structure, was observed by time-resolved PL method to estimate the quality of epilayers in the DH structure. The PL decay time strongly depended on Al content ( x ) of the Al x Ga 1− x As preliminary layer, and the highest value was obtained when the x was 0.25. A PL decay time above 20 ns was successfully obtained for the DH structure grown on the buffer layer structure, which consisted of a 0.05 μm thick Al 0.25 Ga 0.75 As layer and a 1 μm thick GaAs layer. Although this value was half of that for the DH structure grown on GaAs substrate, it was much longer than the value of 3 ns for the DH structure grown on Ge substrate with a conventional GaAs buffer layer 1 μm thick.

Influence of doping concentration on Ni-induced lateral crystallization of amorphous silicon films

Nickel-metal-induced lateral crystallization (MILC) was used to fabricate polycrystalline silicon thin films on glass substrates. Patterned Ni lines were formed on amorphous Si films by a lift-off process using photo resist. The samples were annealed in an N2 atmosphere in a furnace at temperatures ranging from 5501C to 6001C. Both the doping concentration of the Si films and the annealing temperature strongly affected the orientation of the crystals. A p-type poly-Si film with a boron concentration of 5 � 10 19 cm � 3 annealed at 5501C was found to be strongly oriented in the / 22 0S direction. r 2002 Elsevier Science B.V. All rights reserved.

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.