3d-transition-metal-doped ZnO films (n-type Zn1−xMxO (x=0.05–0.25): M=Co, Mn, Cr, Ni) are formed on sapphire substrates using a pulsed-laser deposition technique, and their magnetic and electric properties are examined. The Co-doped ZnO films showed the maximum solubility limit. Some of the Co-doped ZnO films exhibit ferromagnetic behaviors with the Curie temperature higher than room temperature. The magnetic properties of Co-doped ZnO films depend on the concentration of Co ions and carriers.

Bottom-gate-type thin film transistors using ZnO as an active channel layer (ZnO–TFT) have been constructed. The ZnO layers were deposited using pulsed laser deposition at 450 °C at an oxygen pressure of 3 m Torr, and the material that was formed had a background carrier concentration of less than 5×1016 cm−3. A double layer gate insulator consisting of SiO2 and SiNx was effective in suppressing leakage current and enabling the ZnO–TFT to operate successfully. The Ion/Ioff ratio of ZnO–TFTs fabricated on Si wafers was more than 105 and the optical transmittance of ZnO–TFTs fabricated on glass was more than 80%. These results show that it is possible to fabricate a transparent TFT that can even be operated in the presence of visible light.

We report the realization of p-type behavior in ZnO thin films, which are prepared by codoping method using Ga (donor) and N (acceptor) as the dopants. Especially, using active N formed by passing N 2 O gas through an electron cyclotron resonance (ECR) plasma source is quite effective for the acceptor doping. We have observed a room temperature resistivity of 2 •cm and a hole concentration of 4 × 10 19 cm −3. These values are enough high for practical applications in various oxide electronic devices.

We have formed strained dielectric superlattices of BaTiO3 (BTO) and SrTiO3 (STO) by a pulsed laser deposition technique. A large strain of 400–500 MPa is introduced at the interface between the BTO and STO layers. A large dielectric constant of 900 was observed with a stacking periodicity of 2 unit cells/2 unit cells. The superlattices show drastically different electrical behavior from that of the solid solution (Sr,Ba)TiO3 films. Broad maxima of the dielectric constants occur around 40–50 °C and the values remain large even for a temperature above 200 °C.