Molecular beam epitaxy growth of ZnO using initial Zn layer and MgO buffer layer on Si(111) substrates

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We have compared the quality of ZnO films grown on Si(111) substrates by two different methods: (1) initial Zn layer deposition followed by its oxidation and (2) thin MgO buffer layer deposition prior to the growth. All the layers are deposited by molecular beam epitaxy using a radio frequency radical cell. X-ray diffraction measurements reveal that (0001)-oriented ZnO films are grown on Si(111) substrates in both cases. However, the ZnO films grown by using initial Zn layer exhibit straight lines along the principal axes of Si(111) surface. In addition, their x-ray diffraction 2θ/ω spectra often show double peaks. These results are probably caused by the cracks due to the difference in thermal expansion coefficients between ZnO and Si. This phenomenon is alleviated considerably by introducing a thin MgO buffer layer. The samples with thin MgO buffer layer show no double peaks in their x-ray diffraction spectra, and the full width at half maximum value for both 2θ/ω, and ω scan are as narrow as 0.038° and 0.26°, respectively. The photoluminescence emission intensity is also improved by using thin MgO buffer layer.