| Summary: | 博士 === 臺灣大學 === 電子工程學研究所 === 98 === In this dissertation, we report the observation of a polarization-dependent surface plasmon (SP) feature on a 1-D Ag-grating structure through the SP coupling with an InGaN/GaN quantum-well structure beneath the metal grating. Because only the momentum matching condition of the SP component (TM mode) propagating in the direction perpendicular to the grating grooves can be reached through the scattering of the fabricated grating, the SP radiation efficiency is significantly enhanced only in this polarization. Hence, polarized photon output is observed. The dispersion curve of the observed SP mode shifts along the wavenumber axis according to the change of the metal grating period.
Next, the enhanced and partially polarized output of a green light-emitting diode (LED), in which its InGaN/GaN quantum well (QW) couples with surface plasmons on a surface Ag grating structure is demonstrated. Compared with another LED sample of flat Ag coating, the output intensity of the grating LED is enhanced by ~200 % and its polarization ratio reaches 1.51 when the grating period and groove depth are 500 nm and 30 nm, respectively. Based on the comparison with a sample of larger spacing between the metal and QW and numerical simulation, it is concluded that the output enhancement and polarization behaviors are mainly attributed to the QW coupling with localized surface plasmons generated on the grating grooves.
Finally, the output polarization ratio enhancement of an InGaN/GaN quantum well (QW) light-emitting diode (LED) with surface plasmon (SP) coupling by the insertion of a SiO2 layer between the p-GaN layer and a surface Ag grating structure is demonstrated. The insertion of the SiO2 layer is expected to reduce the metal dissipation of SP energy and to further extend the near-field distribution range of induced SP for effectively increasing the SP-QW coupling effect. The Ag grating period for optimizing SP-QW coupling is increased when a SiO2 layer is added to the device that is consistent with the simulation results of the momentum matching of surface plasmon polariton and the resonance of localized surface plasmon. The almost un-polarized outputs from other LED samples fabricated with an epitaxial structure of thicker p-GaN layer, which leads to weak SP-QW coupling, indicate that the observed polarization ratios are due to near-field SP-QW coupling, instead of far-field diffraction
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