Hideo Kidoh

Ferroelectric properties of lead‐zirconate‐titanate films prepared by laser ablation

Ferroelectric lead‐zirconate‐titanate (PZT) thin films have been deposited by excimer laser ablation on sapphire substrates with and without an electrode. In preparation for the films, O2 gas pressure has greatly influenced the film structure and morphology. For the first time, we have confirmed the ferroelectric properties of PZT films prepared by laser ablation without post‐annealing. It appears to be possible to use these films for nonvolatile random access memories with some additional improvements in the film properties.

Nature of Localized States in Hydrogenated Si–Based Amorphous Semiconductor Films Elucidated from LESR and CPM

Measurements of low energy absorption by the constant photocurrent method, ESR and light-induced ESR were carried out for a-Si:H, a-Si1-xCx:H, a-Si1-xOx:H and a-Si1-xNx:H films as a function of the film thickness. As a result, both the surface density of dangling bonds in the disordered surface layer and the density of dangling bonds in the bulk region were obtained by discriminating between neutral and charged dangling bonds. It is found that many charged defects are present even in high-purity a-Si:H films and their density increases with the addition of O and N. We attribute these charged defects to Si3-+N4+ in a-Si1-xNx:H, in contrast to the model of Robertson and Powell, and to Si3-+O3- in a-Si1-xOx:H.

Synthesis of ferromagnetic Bi-substituted yttrium iron garnet films by laser ablation

Bismuth‐substituted yttrium iron garnet (Bi:YIG) films were deposited on gadolinium gallium garnet substrate by laser ablation using the ArF excimer laser. This is the first report on the preparation of Bi‐substituted YIG films by laser ablation. Films have a garnet single phase above the substrate temperature of 490 °C, and the film composition does not deviate largely from the target composition and it is almost constant in the temperature range between 490 and 580 °C. The saturation magnetization of the film is 1500 G at room temperature. Faraday rotation angle θF at a wavelength of 830 nm at room temperature is −0.3×104 °/cm.

Surface and bulk defects in hydrogenated amorphous silicon and silicon-based alloy films

The surface and bulk defects in a‐Si:H, a‐Si1−xCx:H, and a‐Si1−xNx:H films were investigated by electron spin resonance (ESR) and constant photocurrent method. The thickness of the surface defective layer in a‐Si:H films was determined for the first time by ESR. Applying various surface treatments, the free‐surface layer proved to be much more defective than the interface layer. Both surface and bulk defect densities in a‐Si1−xCx:H and a‐Si1−xNx: H alloy films were also determined by ESR. The origin of the surface states is discussed, and the experimental results are explained by a simplified model of the distribution of surface defects.The surface and bulk defects in a‐Si:H, a‐Si1−xCx:H, and a‐Si1−xNx:H films were investigated by electron spin resonance (ESR) and constant photocurrent method. The thickness of the surface defective layer in a‐Si:H films was determined for the first time by ESR. Applying various surface treatments, the free‐surface layer proved to be much more defective than the interface layer. Both surface and bulk defect densities in a‐Si1−xCx:H and a‐Si1−xNx: H alloy films were also determined by ESR. The origin of the surface states is discussed, and the experimental results are explained by a simplified model of the distribution of surface defects.

Preparation of Pb(Zr, Ti)O3 films on Si substrate by laser ablation

Lead-zirconate-titanate (PZT) thin films were prepared on oxidized Si(100)-substrate with a thin film electrode by laser ablation. Ferroelectric perovskite phase was obtained in the PZT films on Ni-alloy/SiO2/Si substrate with the substrate temperature above 500°C, but it was not obtained in the films on Pt/SiO2/Si. The switching voltage of remanent polarization (Pr) decreased with decreasing PZT film thickness. The 0.15-µm-thick film showed Pr of 15 µC/cm2 with a swing voltage of 5 V.

Influence of Laser Fluence on Structural and Ferroelectric Properties of Lead-Zirconate-Titanate Thin Films Prepared by Laser Ablation

Ferroelectric lead-zirconate-titanate (PZT) thin films were deposited by excimer laser ablation on (100) MgO substrates with and without an electrode. The film composition was approximately the same as that of the target over a laser fluence range of 2.6 and 10 J/cm2shot. Increase in the laser fluence enhances the film deposition rate and the crystallite size. In representative experiments, the remanent polarization and coercive field of the film prepared at a laser fluence of 9.2 J/cm2shot were 28 µC/cm2 and 72 kV/cm, respectively.

Influence of Laser Irradiation and Ambient Gas in Preparation of PZT Films by Laser Ablation

Pb(Zr 0.52 Ti 0. 48 )O 3 (PZT) films were prepared on r-plane sapphire substrates by the laser ablation method utilizing ArF excimer laser in O 2 or N 2 O environment. The composition of the films deposited in O 2 environment was found to be fairly close to the composition of the target material for a wide range of substrate temperatures, 400 – 750 °c. Increasing the laser fluence (the laser power density) for the ablation enhances the formation of the perovskite structure rather than the pyrochlore one. Use of N 2 O ambient gas instead of O 2 gas enhances the formation of the perovskite structure of PZT films. Furthermore, it was found that a laser irradiation on the growing film surface during deposition enhances the formation of the perovskite structure.

Photo-created defects in a-Si:H as elucidated by ESR, LESR and CPM

Abstract Combined measurements of ESR, LESR and CPM were carried out both for annealed and light-soaked a-Si:H films with several different thicknesses. These measurements reveal that the increase in the defect density by light-soaking mainly comes from the bulk region. Moreover it was found that the density of neutral dangling bonds is increased remarkably by light-soaking, but the density of charged dangling bonds does not appreciably change. The characteristic energy of the Urbach tail is found to be increased slightly (2 ± 1 meV) by light-soaking. The density of photo-created neutral dangling bonds for the films with less contaminant is similar to that for the conventional films.

Magneto-Optical Characteristics of Bi-Substituted Rare-Earth Iron Garnet Films Prepared by Laser Ablation.

Bismuth substituted rare-earth iron garnet (Bi:RIG) films were prepared on (111) gadolinium gallium garnet (GGG) and glass substrates b laser ablation using the ArF excimer laser. Crystal structure of the garnet phase was obtained above the substrate temperature of about 500° C on GGG substrate without postdeposition annealing and on glass substrate with postdeposition rapid thermal annealing. Films with the easy magnetization axis normal to the film plane were obtained for Bi:DyIG and Ga- or Al-substituted Bi-YIG on GGG substrate. The Faraday hyster- esis loops and the magnetic domain were observed. On the other hand, the easy magnetization axis normal to the film plane was obtained for Bi:DyIG films on the glass substrate with postdeposition rapid thermal annealing.

Ferroelectricity of lead-zirconate-titanate thin films prepared by laser ablation

Lead-zirconate-titanate films were prepared by excimer laser ablation. The coercive field of films deposited on MgO substrates with an electrode was lower than that of films deposited on sapphire substrates. Laser fluence influenced the grain and crystalline size, resulting in a change in the Ec. Film thicknesses were varied over a range from 0.3 to 2.41μm, with the thinnest film showing a large remanent polarization even at an applied effective voltage of 5V.