Naoya Sotani

Fabrication of solution-processed hydrogenated amorphous silicon single-junction solar cells

Hydrogenated amorphous silicon solar cells were fabricated using solution-based processes. All silicon layers of the p-i-n junction were stacked by a spin-cast method using doped and non-doped polydihydrosilane solutions. Further, a hydrogen-radical treatment under vacuum conditions was employed to reduce spin density in the silicon films. Following this treatment, the electric properties of the silicon films were improved, and the power conversion efficiency of the solar cells was also increased from 0.01% to 0.30%–0.51% under the AM-1.5G (100 mW/cm2) illumination conditions.

Directional Crystallizing Si Films with a Fundamental Continuous Wave Yttrium Aluminum Garnet Laser (Zone Melting for Film)

To form large-grained polycrystalline-silicon (poly-Si) films on glass substrates, we propose a new lateral crystallization method, zone melting for film, which uses a high-power fundamental continuous wave yttrium aluminum garnet (CW-YAG) laser and an absorption layer. The lasers infrared light is changed into thermal energy at the absorption layer and heats the amorphous Si (a-Si) film. Next, the Si film is zone-melted and solidified in one direction with a scanning laser beam. By this method, columnar structured Si films were successfully formed with scanning velocities from 400 to 1000 mm/s. Very large typical grains of 1 or 2 µm by few hundreds of µm were obtained on both glass and quartz substrates, and the long axes of the grains were almost parallel to the laser scanning direction. Textures were also observed in these columnar structured Si films. Recombination carrier lifetimes of these films were several times longer than those of conventional low-temperature-processed poly-Si films.

Low-temperature activation method of poly-Si films using rapid thermal annealing

Doped polysilicon (poly-Si) films with a low resistivity have been successfully obtained at a low temperature using novel processing technology, which was combined with the rapid thermal annealing (RTA) and ion-doping methods. P- doped poly-Si films with a sheet resistance of 3k(Omega) /

Thin film transistor device, display device and method of fabricating the same

DAL were achieved with a process temperature 220 degrees C lower than that of the conventional process which combined the RTA and ion implantation methods. The uniformity of sheet resistance for P-doped poly-Si films prepared by the novel process was better that for the excimer laser annealing. The threshold voltage, subthreshold swing and field effect mobility for n-channel thin film transistors with a lightly doped drain structure using the novel process were 2.0V, 0.3V/dec., and 70cm2/V s, respectively.