Kenji Nakatani

Oxygen doping effect on Ge–Sb–Te phase change optical disks

High performance phase change optical recording disk has been developed by using an oxygen-doped Ge–Sb–Te recording layer. The 5×105 overwrite cycles were achieved with this 6 at. % oxygen-doped phase change optical recording disk. The transmission electron microscope observation shows that the crystal grain size was enlarged and the “self-sharpening effect” disappeared with increasing of oxygen concentration. It is thought that the oxygen doping made it easy to grow the uniform large grain size without the self-sharpening effect around the amorphous mark and therefore, the overwrite cyclability of the phase change optical recording disk was improved.

Preparation and Properties of a-Si: H Solar Cells on Organic Polymer Film Substrate

The plasma deposited a-Si: H p-i-n/ITO heteroface solar cell on flexible organic polymer substrate has been studied on the photovoltaic properties and their dependence on the deposition temperature and surface morphology of a-Si: H layer. So far, the conversion efficiency of 6.36% was obtained for the cells on the polymer film substrate by utilizing microcrystalline n-layer instead of amorphous n-layer. This figure is a little lower than that of cells on stainless steel plate and is partly attributed to the larger surface roughness of a-Si: H on organic polymer film.

Design of textured Al electrode for a hydrogenated amorphous silicon solar cell

Textured surface of metal electrodes formed on a polymer film have been studied to take advantage of an optical confinement effect for hydrogenated amorphous silicon (a-Si:H) solar cell. Theoretical considerations and simulated experiments show that an inclination angle of the textured shape larger than 30° causes an optical confinement effect. The suitable textured Al surface was formed by controlling the crystallization of Al in a sputter-deposition process and adopted for back-side electrodes of stainless steel/Al/polymer. Consequently, the short-circuit current (Jsc) was improved by about 10% by using a textured Al layer with homogeneous roughness of 200–400 nm in size. For further enhancement of Jsc, this textured layer was adopted for multilayer electrodes such as Ti/Ag/Ti/Al, and ITO/p-i-n type solar cells formed on this multilayer electrode showed a high conversion efficiency of 11.28%.

A monolithic series-connected solar cell on an organic polymer film substrate

Abstract A new fabrication process of a monolithic series-connected a-Si:H solar cell was investigated. In this process, an Al/SS/a-Si:H/ITO solar cell structure is produced on an organic polymer film substrate by a roll-to-roll sputtering method and a roll-to-roll GD-CVD method. A conversion efficiency of 10.1% was obtained in the small area cell (1.2 cm2). To make a large size monolithic series-connected solar cell, this cell on the film substrate is divided into some unit cells by a combination of YAG laser scribing and screen printing of an organic electrical insulation layer and then each unit cell is inter-connected in series by screen printing of a grid electrode and bonding by the YAG laser. So far, a practical conversion efficiency of 5.5% was obtained in a 20 × 60 cm monolithic series-connected cell on a poly(ethylene terephtalate) (PET) substrate. Various types of modules (flexible, lightweight) were obtained by laminating with another PET film, a polycarbonate sheet, or a glass sheet.

The Influence of Adjacent Preformat Pits on Magneto-Optical Signals

Fluctuations in magneto-optical (MO) signals have been observed in 3.5-in. 640 MB MO disks which have the zone constant angular velocity (ZCAV) format. They were found to occur at the border of each band (zone) when there were preformat pits in the adjacent band. The fluctuations were observed in those MO disks whose substrates were injection molded polycarbonate (PC). The degree of these MO signal fluctuations depended on the injection molding conditions of the substrates and the phase shift of the optical head. It is thought that such phenomena can be attributed to tilted ellipsoids of substrate birefringence that occur around preformat pits, and which are caused by stresses induced around the preformat pits during the injection molding process.