Title page for etd-0719116-165854


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URN etd-0719116-165854
Author Szu-An Lu
Author's Email Address im_lu3@hotmail.com
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Department Materials and Optoelectronic Science
Year 2016
Semester 1
Degree Master
Type of Document
Language zh-TW.Big5 Chinese
Title Epitaxial growth and electric properties of rock-salt Zn1-xMgxO
Date of Defense 2016-08-09
Page Count 103
Keyword
  • ZnO
  • rocksalt
  • MgO
  • molecular beam epitaxy
  • Zn1-xMgxO
  • Abstract Zn1-xMgxO epilayers with x = 0.2~0.8 were grown on MgO (100) substrate by molecular beam epitaxy. The beam equivalent pressure (BEP) of zinc was controlled between 2.5x10-8 and 2.2x10-7 mbar, and that of magnesium was controlled between 1.6x10-8 and 2.5x10-8 mbar to result in Zn/Mg flux ratios of 2.2 to 12.0. Two substrate temperatures, 400 oC and 600 oC, were used for epitaxial growth. The Zn1-xMgxO samples were analyzed by high resolution X-ray diffraction (HRXRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive x-ray spectroscopy (EDS), optical specrtoscopy and transmission electron microscopy (TEM).
    X-ray diffraction shows that the Zn1-xMgxO samples with x>0.2 exhibit a rocksalt crystal structure, whereas those with x<0.15 are composed of rocaksalt and wurtzite phases. Most of the samples exhibit surface roughness values in a range of 8~18 nm according to the AFM analyses. The slightly high roughness is resulted from the co-existence of nano-sized crystals which rotate with respect to the growth direction by 15~45o. These crystals form fine pyramids on the surface and therefore deteriorate the surface smoothness. Samples grown at 400 oC with the ZnO content of 18~62% exhibit lattice constants of 0.423~0.426 nm and full width at half maximum (FWHM) values of (200)ZMO rocking curve in the range of 0.05o to 0.35o. Samples grown at 600 oC with the ZnO content of 24~84% exhibit lattice constants of 0.425~0.427 nm and FWHM values of the (200)ZMO rocking curves of 0.11o~0.39o. Phi scan verifies that the epitaxial layer and the substrate satisfies the cube-on-cube orientation relationship. The reciprocal space map (RSM) analyses confirm that the Zn1-xMgxO epitaxial layer with x>0.76were grown in a pseudomorphic mode according to which the lattice constants of Zn1-xMgxO in the in-plane directions are exactly the same as those of MgO. The lattice constraint on the Zn1-xMgxO epitaxial layer with x<0.43 is partly relaxed and the misfit dislocations generated on strain relaxation deteriorate the FWHM of the (200)ZMO rocking curves. In addition, the lattice constant of rocksalt ZnO is derived to be 0.4278 nm by extrapolating the lattice constants of the Zn1-xMgxO samples. The energygap values of the rocksalt Zn1-xMgxO epilayer with x=0.2 to 0.8 are in a range of 4.6~6.0 eV derived from their transmittance spectra.
    Advisory Committee
  • New-Jin Ho - chair
  • Hsinglu Huang - co-chair
  • Liuwen Chang - advisor
  • Files
  • etd-0719116-165854.pdf
  • Indicate in-campus at 5 year and off-campus access at 5 year.
    Date of Submission 2016-08-30

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