Improvement of crystallinity and surface roughness in epitaxial CeO₂/Ce_1-xZrxO₂/Y_0.15Zr_0.85O_1.93 buffer layers deposited on a Si(100) substrate by pulsed laser deposition

Epitaxial CeO₂/Ce_1-xZr_xO₂/Y_0.15Zr_0.85O_1.93 (YSZ) buffer layers were fabricated on a Si(100) substrate by pulsed laser deposition, and its crystallinity and surface roughness were analyzed. When Ce_1-xZr_xO₂ (x = 00.6) films were directly deposited on the Si(100) substrate, the films had a (111) or (111)-preferred orientation. In contrast, (100)-oriented epitaxial films of the Ce_1-xZr_xO₂(x = 00.6) were obtained by introducing a 2.5-nm-thick YSZ buffer layer between Ce_1-xZr_xO₂ and Si. Lattice parameters and surface roughness of the Ce_1-xZr_xO₂ layers on the YSZ-buffered Si(100) decreased from 0.542 to 0.525nm (in-plane) and 0.47 to 0.12 nm, respectively, as the increase of x from 0 to 0.6. After that, an epitaxial CeO₂/Ce_0.4Zr_0.6O₂/YSZ buffer layer was fabricated on the Si substrate. Differences in lattice parameters between CeO₂ and Ce_0.4Zr_0.6O₂ and also between Ce_0.4Zr_0.6O₂ and YSZ became about half of that between CeO₂ and YSZ. As a result, surface roughness of the CeO₂ layer on top of the Ce_0.4Zr_0.6O₂/YSZ/Si and full width at half maximum of the rocking curve of the CeO₂ (004) reflection became 0.18nm and 0.89 degrees, respectively, which were smaller than those of CeO₂ layers deposited directly on YSZ/Si.