Design And Fabrication Of Polarized White LEDs Based On Fluorescent Ceramics And Nano-Gratings

Solid-state white light source based on light-emitting diode(LED) has been widely used in various fields, e.g., solid-state lighting and backlighting in liquid crystal display(LCD), because of its high luminous efficiency and long lifetime. With the increasing development of white LEDs, polarized white source, as an important functional expansion, has been increasingly demanded in many applications, e.g., CCD polarization imaging, optical storage, optical communication, photoelectric detection, and flat panel display. In this thesis, a systematic investigation on the design and fabrication of an integrated high linearly polarized white light emission from a GaN based LED is presented. The major work includes:(1) A novel GaN based white LED structure with dielectric/metal nano-gratings integrated fluorescent ceramics has been proposed, from which high linearly polarized white light emission(450nm~650nm) can be obtained. By introducing an MgF2 dielectric layer of low refractive index between the fluorescent ceramics and the nano-gratings, both TM transmission and extinction ratio of this composite structure can be effectively improved. Finite difference time domain(FDTD) method is used to design and analyze the polarization performance and characteristics of the composite structure, and optimized parameters of the structure has been obtained.(2) Experimental fabrication and characterization of the proposed device have been performed. A dielectric/metal nano-gratings structure with a period of 150 nm and an area of 20mm×20mm via nanoimprint lithography(NIL) and reactive ion etching(RIE) techniques has been successfully obtained. This structure is then integrated with a blue GaN-LED to generate a polarized white light emission. A measurement system for the performance of polarization emission of the fabricated device is built. Experimental resultsshow that an extinction ratio of higher than 20 dB in a widely angle(±60°) and a TM transmission of 60% in the visible range(450nm-650nm) can be obtained, which agrees well with the theoretical design.