| Summary: | 碩士 === 國立中興大學 === 精密工程學系所 === 99 === We study the growth mechanism of epitaxial ZnO thin film, based on first-principles density function calculations. A detailed analysis of the preferred (epitaxial) orientation of ZnO strained layer superlattices is examined. The epitaxial softening of (0001)-oriented Zn1-x(Be,Mg,Al)xO strained layer lattices are investigated, and the ZnO strained layers could be stabilized with adding the aluminum compositions, and <2-1-10>-oriented ZnO is more stable than (0001)- or (10-10)-oriented ZnO. Using the harmonic elasticity theory, we find the qharm([0001]) is the highest and the qharm([2-1-10]) is much softer than <0001> or <10-10>. In addition, the slightly softening of <11-2l> in Zn1-x(Be,Mg,Al)xO strained layer lattices is observed. Applying the surface formation energy method, we find (2-1-10) oriented surface is the dominated orientation in ZnO epitaxial process, but ZnO will changes its preferred orientation form the (2-1-10) to (0001) O-terminated ZnO under O-rich condition. Furthermore, our result also indicates that the preferred termination of the ZnO (0001) surface is O-terminated ZnO (0001) polar surface. A comparison of surface formation energy between bare ZnO surface and hydrogenated ZnO surface shows the non-polar ZnO surface is more sensitive than polar surface. The significant variation of surface energy has the dramatic effects on surface morphology and results a rough surface for non-polar ZnO surface.
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