| Summary: | 博士 === 國立中山大學 === 材料與光電科學學系研究所 === 103 === This thesis is focused on the growth of nonpolar ZnO film on LiGaO2 (LGO) substrate by plasma assisted molecular beam epitaxy (PAMBE) method. According to small lattice mismatch between ZnO and LGO substrate, high-quality ZnO film should be acquired after MBE growth process. However, the growth of ZnO film suffered undesired failure. The inference of this failure was attributed to the influence of pretreatments on LGO substrate, the surface cleaning process using activated hydrogen in Load Lock chamber of MBE system in particular. In order to prove the relationship between H2 and growth of ZnO, the comparison of nonpolar ZnO film adopting with and without H2 cleaning process is investigated. Therefore, this thesis reports in two major parts.
In first part, nonpolar ZnO films were successfully grown on LGO substrate by MBE method as we removed H2 cleaning process. The orientation relationship between nonpolar m-plane ZnO and LGO substrate was confirmed as (11 ̅00) ZnO // (100) LGO, [0001] ZnO // [001] LGO by selected area electron diffraction patterns (SAED). X-ray diffraction (XRD) patterns have indicated that higher growth temperature of ZnO epilayer leads to better crystal qualities. Nevertheless, the irregular ZnO growth might be induced by residual clusters on the surface of LGO substrate since H2 cleaning process was canceled.
The second part further discusses the influence of activated H2 on the surface of LGO substrate by atomic force microscope (AFM). The excessive H2 cleaning process destroyed the surface of LGO and resulted in the failure of ZnO crystal growth. By comparing H2 cleaning process with different parameters, the residual clusters on surface of as-received LGO substrate can be removed by activated H2 under appropriate cleaning conditions and preserve the completeness of substrate. Under such condition, m-plane ZnO films grown on (100) LGO substrate possess good crystal quality. The optimal growth temperature of m-plane ZnO is around 600℃ and the FWHM of (11 ̅00) ZnO X-ray rocking curve is around 0.07°. The microstructure defects of m-plane ZnO is investigated by transmission electron microscope (TEM). Optical properties of ZnO epilayer are characterized by room temperature photoluminescence (PL).
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