Study on the optical of Zn1-xBexSe alloys
| Autor: | Ling Ying Lin, 林玲穎 |
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| Rok vydání: | 2003 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 91 We present the studies on the optical properties of Zn1-xBexSe epitaxial layers（x=0, 3.14 ﹪, 5.43 ﹪, 9.13 ﹪）grown by molecular beam epitaxy on GaAs（001）substrates by photoluminescence（PL）and Raman scattering spectra. By comparing the differences of the optical properties between ZnSe-binary and Zn1-xBexSe-ternary alloys, we discover several novel results, which are very useful both for academic as well as industrial application. Ⅰ. Chaotic oscillations induced by excitons self-trapping in ZnSe-BeSe alloys The luminescence spectra of ZnBeSe alloys are dominated by the fairly strong peak with a Stokes shift. The observed unusual features are very different from those expected by alloy potential fluctuations. Considering the difference in electron affinity between Zn and Be atoms and the lattice distortion, we point out that the dominant emission can be attributed to the occurrence of excitons self-trapping induced by isolated Be atoms. Quite interestingly, we discover that the self-trapped excitons in ZnBeSe system can drive the chaotic oscillations in the temporal changes of the conventional photoluminescence measurement, which is quite different from the chaotic current or voltage oscillations in previous reports. The impact ionization of self-trapped excitons is suggested to be responsible for the observed chaotic oscillations. Ⅱ. Raman investigation of anharmonicity and disorder-induced effects in Zn1-xBexSe alloys For vibrational properties, Raman scattering of Zn1-xBexSe have also been studied. We have investigated the effect of compositional disorder in Zn1-xBexSe by analyzing the broadening and asymmetry of the first-order LO mode. We find that the best fit of Raman line shapes for the ZnSe-like LO mode in Zn1-xBexSe alloys can be obtained using the spatial correlation model. We have also analyzed comparatively the anharmonic effects due to temperature and compositional fluctuations in ZnSe and ZnBeSe systems, using temperature-dependent Raman scattering between 6 and 306 K. It is found that the anharmonicity is higher for ZnBeSe alloys than ZnSe and it increases with compositional disorder. Therefore, both temperature- and compositional-fluctuations-induced anharmonicities can introduce changes in the linewidth, line center position, and anharmonic decay time of first-order optical phonons in Zn1-xBexSe alloys. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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