No abstract

The metalorganic chemical vapor deposition (MOCVD) technique has been applied to the growth of epitaxial Pb1−xLaxTiO3 (PLT) thin films with x=0.28. By first introducing an initial TiO2 layer, three-dimensional epitaxial PLT films were grown on the (100) surface of MgO substrate. For both KTaO3 (100) and Al2O3 (0001) substrates, heteroepitaxy was achieved without the introduction of TiO2 as the initial, intervening layer between the PLT film and the substrate. On Al2O3 substrates, PLT films with a [111] preferred orientation were grown with a good epitaxial in-plane relationship.

The Laguerre polynomial technique is an efficient method which can be used to solve the field equations of surface acoustic wave (SAW) propagation. In this paper field distributions and velocities in multilayered structures are obtained by this simple and noniterative method. Formulations are given for open-and short-circuit boundary conditions. Calculations for the SAW velocity of a ZnO film on a silicon substrate are presented and these are compared with other calculations from the literature. Numerical results are also given for GaAs/AlGaAs multilayered structures.

Metalorganic chemical vapor deposition (MOCVD) was used to prepare epitaxial or highly oriented PLT (Pb1-xLaxTiO3) thin films with x in the range of 0.21 to 0.34. The growth of PLT films resulted in three-dimensional epitaxial heterostructures on (100) surface of the MgO and the KTaO3 substrates. The PLT film grown on the KTaO3 (100) substrate has a significantly lower minimum channeling yield compared to that on the MgO (100) substrate because of the smaller lattice mismatch. The thickness and the refractive indices in the wavelength range of 435 to 1,523 nm were measured by the prism coupling method. The measured film thickness of 570 nm was in good agreement with that from RBS measurements. The refractive index of PLT film is smaller than that of PbTiO3, its difference at 632.8 nm is about 2.5 %. The dispersion of the refractive index was well fitted to a Sellmeier dispersion formula.

GaAs has been employed as a material for ACT devices because it is a piezoelectric semiconductor. However, because GaAs is such a weakly piezoelectric material, the SAW I D T drive power required to achieve charge transport is typically about 27dBm. An enhancement of the piezoelectric coupling could potentially improve device lifetime, reliability, dynamic range and decrease power consumption. To this end we are investigating the use of a ZnO film on top of the A C T substrate to enhance the piezoelectric coupling. Moreover, the ZnO film structure would also make it possible to construct monolithic devices with ordinary SAW devices and GaAs electronics. In order t o provide a basis for the design of such devices, we have reported surface acoustic wave properties, including effective piezoelectric coupling constant, slowness surface, and propagation loss, measured on sputtered ZnO film overlayed { 100)-cut (110)-propagating GaAs substrates. T h e measurements have been performed on the different thicknesses of the film over the range of 1 . 6 4 p m and with films of different grain sizes. IDTs operating between 180 and 360MHz were fabricated, and a knife-edge laser probe was used to measure the SAW propagation. T h e measured data is compared with theoretical values.