| Summary: | 碩士 === 國立臺灣大學 === 光電工程學研究所 === 102 === In the thesis, we study the structural properties of GaPSb and GaAsPSb alloys. Results from reciprocal space mapping and Raman scattering spectra suggest that long-range order remains in these alloys. However, we also find a behavior of one bond → two modes along with broad line width and asymmetry. We believe that the atoms deviate from their minimum energy sites because of bond distortion or short-range disorder, leading to strong anharmonic effect, which cause the attenuation of phonon wave. Therefore, we use spatial correlation model to fit the broad and asymmetric line shape successfully. In addition, we also use synchrotron radiation X-ray to measure the X-ray absorption of these alloys. From the fitting results of extended X-ray fine structure, we know the bond length is prone to be its binary one; so the major ingredient of bond distortion is bond bending. In order to further study of bond distortion. We utilize valence force field model to calculate the distortion of the atoms on a supercell of 1000 atoms. We find that the nearest neighbor atoms affects the phonon dispersion relation. In a Ga-centered tetrahedral unit cell with 2P2Sb atoms of GaPSb supercell, the stretching energy of Ga-P bond is very small but bending energy is the strongest. We ascribe the GaP-like LO+ line shape with better symmetry to the contribution of Ga-P bond in 2Sb2P unit cell. On the other hand, in GaAsPSb supercell, the 1As1P2Sb unit cell with the lowest bond stretching energy should have made contribution to the LO+ line shape, but the formation probability of this cell is too low to have an effect on the spectra. So, we only can observe GaP-like LO mode in GaAsPSb Raman spectra.
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