Compositional dependence of optical critical point parameters in pseudomorphic GeSn alloys
| Autor: | Vijay Richard D'Costa, Qian Zhou, Eng Soon Tok, Yee-Chia Yeo, Wei Wang, T. K. Chan, Thomas Osipowicz |
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| Rok vydání: | 2014 |
| Předmět: | |
| Zdroj: | Journal of Applied Physics. 116:053520 |
| ISSN: | 1089-7550 0021-8979 |
| DOI: | 10.1063/1.4892105 |
| Popis: | Spectroscopic ellipsometry was used to investigate the optical response of pseudomorphic Ge 1− x Sn x (0 ≤ x ≤ 0.17) alloys grown directly on Ge (100) by molecular beam epitaxy. A detailed compositional study of amplitudes, broadenings, energies, and phase angles associated with critical points E 1, E 1 + Δ1, E 0 ′ , and E 2 of GeSn alloys was carried out using a derivative analysis. The results can be understood in terms of the electronic bandstructure of Ge or relaxed GeSn alloys with the following differences. First, broadening parameters in pseudomorphic alloys are found to have lower values compared to relaxed alloys indicating lower dislocation density in our pseudomorphic alloys relative to relaxed alloys. Second, the amplitudes of E 1 and E 1 + Δ1 are enhanced and reduced, respectively, with respect to relaxed GeSn alloys, and the trends are captured using the k.p method as a biaxial stress induced effect. Third, phase angles are lower than Ge for all the critical points suggesting reduction of excitonic effects in GeSn with respect to Ge. |
| Databáze: | OpenAIRE |
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