By chemical liquid deposition in which an alkoxide with a carbon number of 4 or smaller was used as raw material, a Sr0.7Bi2.3Ta2O9+α (SBTO) thin film was fabricated for use as a ferroelectric memory device for the purpose of decreasing the temperature of crystallization and improving surface morphology. The crystallization process was also examined. Crystallization began when the film was heat treated in oxygen at 650° C. When it was heat treated at higher than 700° C, it showed ferroelectric properties, and the squareness (remanent polarization/saturation polarization) of its hysteresis loop was improved at 800° C. A film heat treated at temperature 650° C was a cluster of fine particles, and a film heat treated at 800° C was a cluster of large particles. A film heat treated at 700° C was a mixture of fine particles and large particles. Therefore, it is concluded that the alkoxide with a carbon number of 4 or smaller as raw material enable the lowering of the heat-treatment temperature and improvement of the surface morphology of SBTO thin films.

The crystallographic and electroluminescent characteristics of ZnS:Mn thin films prepared by radio frequency ion plating techniqueThe dependences of brightness, emission efficiency 1], average electric field E A , conduction current J A , and emission lifetime T upon the device parameters such as film thickness, substrate temperature during evaporation, and Mn concentration have been systematically investigated in ZnS:Mn thin-film electroluminescent devices. The value of 1] increases rapidly with film thicknesses below 3000 A but E A decreases slowly. These results can be explained by the increase of the crystallinity of the ZnS:Mn films. The value of 1] increases with the Mn concentration and reaches its maximum at about 0.45 wt %. At above this Mn concentration, 1] and T decrease rapidly, EA increases, and J A decreases slowly. These results may be attributed to a decrease of hot electron energy and/or an increase of the nonradiative transition probability of the excited Mn centers. The brightness-voltage (B-V) hysteresis characteristic is observed in this Mn concentration region. This memory effect is also discussed. PACS numbers: 78.60.Fi 85.60.Jb ...--"n· .... ·Mn 6000A ,3000A Electrolu minescence FIG. I. Typical structure of a ZnS:Mn EL device.

Recessed gate AlGaN/GaN high electron mobility transistors (HEMTs) grown on sapphire substrate have been fabricated. In order to improve FET performances, we optimized the layer structure and the electrode arrangement of the HEMT, and hence 0.15 μm gate‐length AlGaN/GaN‐HEMTs with recessed gate were successfully fabricated and the obtained transconductance was as high as 450 mS/mm. In this paper we describe the improvement of HEMT layer structures on sapphire substrate, the optimisation of an offset arrangement of gate electrodes, and the results of DC/RF measurements of our HEMTs. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A systematic investigation of the electroluminescent (EL) ZnS thin film devices doped with rare earth centers, SmF3 (red), TbF3 (green), and TmF3 (blue), is made to examine the possibility of multicoloring. Various characteristics, such as brightness, emission efficiency, decay time, EL spectra, and their concentration dependences are measured. The number of photons emitted from these devices is also estimated to discuss quantum efficiencies. For SmF3 and TmF3 activators, it is found that concentration quenching of EL emission takes place through non‐radiative crossrelaxation process. No such quenching is observed for TbF3 activators. In TmF3 activators, most of the radiative energy is found to be emitted in the infrared region. The impact excitation cross‐section for these rare earth compounds is also inferred to be lower compared with that of Mn2+ ions.