Search

Liquid phase epitaxy (LPE) has a great potential in producing low-cost, high-current, coated conductors due to its fast growth rate in excess of 1 µm min⁻¹ and the capability of growing thick films up to 10 µm without degrading the structural perfection or J_c. The main problem for LPE is the chemical reaction between the films and substrates at elevated growth temperatures. Former efforts have been focused on the reduction of growth temperatures. This has been proved to be unsuccessful due to the limited degree of temperature reduction; reducing the growth temperature also reduces the solubility of YBCO in the liquid, making the growth even more difficult. An alternative solution to this problem is to search for a special buffer which is particularly resistant to the attack of the high-temperature liquid. We have recently developed a new buffer, Nd₂CuO₄, which was very stable in the cuprate solution at temperatures around 950 °C and therefore extremely useful for LPE. Initial growth of YBCO on Nd₂CuO₄ buffered, surface oxidized Ni substrates showed a sharp superconducting transition at 90 K and transport J_c over 10⁵ A cm⁻² (77 K). Although YBCO could be grown on Nd₂CuO₄ by LPE without any other intermediate seed layer, growth of Nd₂CuO₄ on both sides of the NiO/Ni substrate with 100% coverage was not easy and had a low success rate. Complete coverage of Nd₂CuO₄ buffer on the NiO/Ni substrates was the critical step to avoid Ni contamination and achieve a high J_c.

Not Available

Effects of postdeposition annealing (PDA) in N2O ambient on metal-organic decomposed CeO2films deposited on GaN substrate had been reported. The utilization of N2O gas during PDA had successfully suppressed the decomposition of GaN as revealed by x-ray diffraction (XRD). XRD had detected the presence of CeO2and α-Ce2O3phases, wherein the phase transformation of CeO2to α-Ce2O3led to the formation of β-Ga2O3interfacial layer (IL). Formation of IL comprising of Ga–O and Ga–O–N compounds in CeO2/GaN system was verified by dark-field scanning transmission electron microscope image and energy dispersive x-ray line profile, respectively. The metal–oxide–semiconductor characteristics of CeO2/GaN structure showed a change of negative to positive effective oxide charge (Qeff) and increasing interface-trap density (Dit) as a function of PDA temperature. The highest oxide breakdown field demonstrated by 1000°C-annealed sample was correlated with Qeffand Dit. A detailed explanation on this correlation as well as current transport mechanism in these oxides has been presented.

Cerium oxide (CeO2)solution was prepared by cerium(III) acetylacetonate hydrate, methanol, and acetic acid as the starting materials via the metallorganic decomposition (MOD) method. Postdeposition annealing was performed onto the MOD-derived CeO2films deposited onto n-type Si substrates at different temperatures (600, 800, and 1000°C) under the flow of argon gas. A slow cooling rate was then accomplished for samples to cool down to room temperature. Four orientations [(111), (200), (220), and (311)] of CeO2films were revealed by X-ray diffraction analysis as well as α-Ce2O3and cerium silicate (Ce2Si2O7). Epitaxial-like behavior was shown in the sample annealed at 600°Cdue to the (200)-oriented CeO2film, and the dominance of this plane ceased with the increase in annealing temperature. A negative voltage shift was observed in all of the samples, indicating that positive oxide charges were trapped in the oxide as a result of the presence of oxygen vacancies. An interface trap density was extracted from the capacitance–voltage measurement, and it was related to the current density–voltage characteristics of the investigated samples. The lowest density was perceived by the sample annealed at 1000°Cdue to the increment in the Ce2Si2O7layer, reduction in total interface trap density, and effective oxide charge.