Abstract:We have investigated surface morphology of YBa2Cu3O7−y thin films prepared by chemical vapor deposition (CVD) using liquid metalorganic (MO) sources on MgO(100) single crystalline substrates by atomic force microscopy (AFM). An abrupt change in the terrace width was observed at the deposition temperature of around 750 °C. An anomalous decrease in the efficiency of incorporation of the yttrium component into the film was also found above the same temperature. It suggests that the appearance of liquid phase on t… Show more
“…Solid source precursors, while easy to handle, are prone to sintering, which progressively lowers the surface area (for this type of precursor, deposition is typically diffusion-limited) and gives rise to time- dependent volatilization rates. In contrast, liquid precursors have a constant surface area that provides stable precursor delivery. − A Cd(hfa) 2 (TMEDA) analogue with a lower melting point would be highly desirable if it were a liquid at standard MOCVD growth reactor-operating temperatures, while maintaining robust thermal properties. It is well-established that appropriate substitutions at the ligand periphery can be used to tailor melting points in related types of Group II precursors without deleterious impact on volatility or thermal stability. , Complementary approaches to low-melting cadmium precursors have very recently been reported. , …”
A series of low-melting, thermally stable cadmium metal-organic chemical vapor deposition (MOCVD) precursors have been synthesized, structurally and spectroscopically characterized, and implemented in growth of highly conductive and transparent CdO thin films. One member of the series, bis(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato)(N,N-diethyl-N',N'-dimethyl-ethylenediamine)cadmium(II), Cd(hfa)(2)()(N,N-DE-N',N'-DMEDA), represents a particularly significant improvement over previously available Cd precursors, owing to the low melting point and robust thermal stability. High-quality CdO films were grown by MOCVD on glass and single-crystal MgO(100) between 300 and 412 degrees C. Film growth parameters and substrate surface have large effects on microstructure and electron carrier transport properties. Enhanced mobilities observed for highly biaxially textured films grown on MgO(100) vs glass are attributed, on the basis of DC charge transport and microstructure analysis, to a reduction in neutral impurity scattering and/or to a more densely packed grain microstructure. Although single-grained films grown on MgO(100) exhibit greater mobilities than analogues with discrete approximately 100 nm grains and similar texture, this effect is attributed, on the basis of charge transport and Hall effect measurements as well as optical reflectivity analysis, to differences in carrier concentration rather than to reduced grain boundary scattering. Unprecedented conductivities and mobilities as high as 11,000 S/cm and 307 cm(2)/V.s, respectively, are obtained for epitaxial single-grained films (X-ray diffraction parameters: fwhm(omega) = 0.30 degrees, fwhm(phi) = 0.27 degrees ) grown in situ on MgO(100) at a relatively low temperature (400 degrees C).
“…Solid source precursors, while easy to handle, are prone to sintering, which progressively lowers the surface area (for this type of precursor, deposition is typically diffusion-limited) and gives rise to time- dependent volatilization rates. In contrast, liquid precursors have a constant surface area that provides stable precursor delivery. − A Cd(hfa) 2 (TMEDA) analogue with a lower melting point would be highly desirable if it were a liquid at standard MOCVD growth reactor-operating temperatures, while maintaining robust thermal properties. It is well-established that appropriate substitutions at the ligand periphery can be used to tailor melting points in related types of Group II precursors without deleterious impact on volatility or thermal stability. , Complementary approaches to low-melting cadmium precursors have very recently been reported. , …”
A series of low-melting, thermally stable cadmium metal-organic chemical vapor deposition (MOCVD) precursors have been synthesized, structurally and spectroscopically characterized, and implemented in growth of highly conductive and transparent CdO thin films. One member of the series, bis(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato)(N,N-diethyl-N',N'-dimethyl-ethylenediamine)cadmium(II), Cd(hfa)(2)()(N,N-DE-N',N'-DMEDA), represents a particularly significant improvement over previously available Cd precursors, owing to the low melting point and robust thermal stability. High-quality CdO films were grown by MOCVD on glass and single-crystal MgO(100) between 300 and 412 degrees C. Film growth parameters and substrate surface have large effects on microstructure and electron carrier transport properties. Enhanced mobilities observed for highly biaxially textured films grown on MgO(100) vs glass are attributed, on the basis of DC charge transport and microstructure analysis, to a reduction in neutral impurity scattering and/or to a more densely packed grain microstructure. Although single-grained films grown on MgO(100) exhibit greater mobilities than analogues with discrete approximately 100 nm grains and similar texture, this effect is attributed, on the basis of charge transport and Hall effect measurements as well as optical reflectivity analysis, to differences in carrier concentration rather than to reduced grain boundary scattering. Unprecedented conductivities and mobilities as high as 11,000 S/cm and 307 cm(2)/V.s, respectively, are obtained for epitaxial single-grained films (X-ray diffraction parameters: fwhm(omega) = 0.30 degrees, fwhm(phi) = 0.27 degrees ) grown in situ on MgO(100) at a relatively low temperature (400 degrees C).
“…These groups clarified that the LPE could achieve an excellent crystallinity and a quasi-atomically flat surface. On the other hand, Yoshida et al substantiated that the quasi-liquid phase growth was observed in metal organic chemical vapor deposition on an YBa 2 Cu 3 O y (YBCO) thin film [10], just as observed in the vapor-liquid-solid (VLS) growth. Moreover, Yun et al demonstrated that the NdBa 2 Cu 3 O y (NdBCO) thin films fabricated by tri-phase epitaxy using Ba-Cu-O flux which is substantially same with VLS showed a high T c of 94 K which had the surface morphology consisted of flat terraces with a width of $200 nm and a step height of 1.2 nm [11].…”
“…For example, an abrupt change in film growth morphology at a specific substrate temperature during MO-CVD has been explained in terms of the formation of a quasi-liquid surface layer at the higher temperatures, leading to a change from conventional vapour growth to something termed vapourliquid-solid growth. 82 This concept has been extended in a technique called tri-phase epitaxy, in which components are supplied to a liquid layer on a growing film surface. 83 Such growth by diffusive transport across a thin liquid flux layer has also been termed hybrid LPE.…”
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