Oxidation by the UV & ozone process, nitridation by the nitrogen helicon-wave-excited plasma process, and the combination of these processes are applied to (100) GaAs wafers. An atomic force microscope, X-ray photoelectron spectroscopy, a transmission electron microscope, photoluminescence and electrical characteristics (current-voltage and capacitance-voltage) were used to analyze the influences of these processes on the structure and composition of the surfaces and the interfaces. Metal-insulator-semiconductor (MIS) diodes and Schottky diodes were fabricated in order to investigate the electrical influences of these processes. The oxidation slightly disorders GaAs surfaces. Nitridation of a bare surface creates about a 2nm-thick strongly disordered layer, which strongly deteriorates the electrical and photoluminescence characteristics. Nitridation of oxidated wafers (oxi-nitridation) forms firm amorphous GaON layers, which contain GaN, with very flat and sharp GaON/GaAs interfaces, where crystal disorder is hardly observed. It improves the current-voltage (I-V) and capacitance-voltage (C-V) characteristics and the photoluminescence intensity. Results of the structural and the electrical characterizations qualitatively coincide well with each other.
Highly [100]-oriented Pb(Zr, Ti)O3 (PZT) films were prepared on (100) GaAs and (100) Si substrates with MgO buffer layer by pulsed laser ablation (PLA). The depth profile of the constituent elements observed by X-ray photoelectron spectroscopy (XPS) shows that there are no remarkable interdiffusion and/or no formation of an alloying layer at both interfaces between PZT and MgO and between MgO and GaAs substrate. The [100]-oriented perovskite PZT films which exhibit the ferroelectric hysteresis loop were obtained on (100) Si substrate with MgO buffer layer with the thickness of only 50 Å, showing that this technique promises the realization of metal-ferroelectric-semiconductor field-effect transistors (MFS-FETs).
Pb(Zr0.52Ti0.48)O3 films were prepared on an r-plane sapphire substrate by laser ablation using the ArF excimer laser. This is the first report on the preparation of Pb(Zr0.52Ti0.48)O3 films by laser ablation. The composition of the deposited films was found to be fairly close to the composition of the target material for a wide range of the substrate temperature, 400–750°C. The substrate temperature greatly influences the crystal structure; a low substrate temperature produces a pyrochlore phase and a high substrate temperature (750°C) a perovskite phase.
The effect of annealing on a MgO substrate was systematically investigated, varying the annealing temperature, for preparation of high-quality YBa2Cu3O
x
(YBCO) films by pulsed laser ablation. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were carried out for characterization of the MgO substrate, and X-ray diffraction (XRD) measurement, including θ-2θ scan, ω-scan (rocking curve) and φ-scan, and electrical measurement were carried out for characterization of YBCO films. Thermal annealing of MgO above 1000° C in oxygen ambient was found to give rise to a great improvement of the crystallinity and the reproducibility of crystal orientation of YBCO films, while it was also found to induce Ca segregation on the surface of MgO and reduce the oxygen content of YBCO films. Annealing below 1000° C causes no outstanding improvement in the crystal structure of YBCO.
On the MgO substrate annealed at 1200° C c-axis-oriented YBCO film was found to reproducibly show a full width at half-maximum (FWHM) of the rocking curve of 0.3°, an FWHM of (005) diffraction of 0.1°, an epitaxial relation without in-plane misorientation, a critical zero temperature of 89 K, and a critical current density of 106 A/cm2 at 77.4 K and zero field.
Silicon nitride (SiN x ) films on Si and poly(ethylene terephthalate) (PET) substrates were prepared at approximately 150 C by catalytic chemical vapor deposition (Cat-CVD), using a SiH 4 /NH 3 gas mixture. A water vapor transmission rate as low as 0.2 g/m 2 day and an O 2 gas transmission rate of 0.6 cm 3 /m 2 day were achieved for a stoichiometric Si 3 N 4 film of 77 nm thickness. Although these transmission rates depended on N/Si ratio, no optical absorption was observed under preferable deposition conditions.
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