| Autor: |
Rodríguez-Fernández C, Almokhtar M; Physics Department , Assiut University , Assiut 71516 , Egypt., Ibarra-Hernández W; Applied Physics Department , West Virginia University , Morgantown , West Virginia 26506-6315 , United States.; Facultad de Ingeniería-BUAP , Apartado Postal J-39 , Puebla 72570 , Mexico., de Lima MM Jr, Romero AH; Applied Physics Department , West Virginia University , Morgantown , West Virginia 26506-6315 , United States.; Facultad de Ingeniería-BUAP , Apartado Postal J-39 , Puebla 72570 , Mexico., Asahi H; The Institute of Scientific and Industrial Research , Osaka University , 8-1 Mihoga-oka , Ibaraki , Osaka 567-0047 , Japan., Cantarero A |
| Abstrakt: |
Wurtzite semiconductor compounds have two silent modes, B 1 l and B 1 h . A silent mode is a vibrational mode that carries neither a dipole moment nor Raman polarizability. Thus, they are forbidden in both infrared reflectivity and Raman spectroscopy. Astonishingly, we detected the B 1 l mode in high-quality, ultra-narrow GaN nanowires using resonant Raman scattering, although the B 1 h was not observed, and there is no immediate explanation for this asymmetric finding. The Raman experiments were performed using several laser lines from 647 to 325 nm; the latter is a wavelength in which Raman becomes resonant. Actually, we observed the B 1 l mode only in resonance, indicating that the appearance of this mode is related to Fröhlich electron-phonon interactions; i.e., a dipole moment emerging in the B 1 l silent mode may not be present in the B 1 h mode. To shed light onto the physical origin of these observations, we performed density functional theory calculations of the lattice dynamics in GaN. We performed a careful analysis of the different physical mechanisms that allow the forbidden mode to appear to explain the physics underlying the nonzero dipole moment in the B 1 l mode, and the reason why this dipole moment is not present in the B 1 h mode. |
