We report on the development of a temperature-dependent electroluminescence experimental setup for characterizing the internal quantum efficiency (IQE) of high-brightness GaN-based light-emitting diodes (LEDs). A systematic IQE study of commercial LED chips from major LED manufacturers (including Cree, Nichia, Osram, and Sanan) is presented. The chips show distinctive temperature- and current-dependence in the IQE behavior. Analysis to correlate the onset of droop with the onset of high injection is also presented.
Fluorescence has important applications in chemical and biological sensing and analysis due to the large selection of
fluorescent markers and their specificity in staining. In order to achieve high sensitivity, the strength and the collection
efficiency for the fluorescence signal is a critical issue that needs to be addressed. In this paper, we study the use of one
dimensional photonic band gap (1D PBG) structures to enhance the florescence excitation and collection. The 1D PBG
structure is designed to create an enhanced evanescent field for the excitation wavelength at the interface of last layer of
the PBG and the sample. Meanwhile, the 1D PBG also serves as an omnidirectional reflector for the florescence signal,
leading to higher collection efficiency. The combination of both effects provides a significant enhancement of
florescence signal. In order to verify the feasibility, GaP/SiO2 multilayer thin film stack is designed and fabricated. High
quality GaP/SiO2 multilayer thin film stack is fabricated using sputtering technique. The sputtered GaP thin film is
characterized using ellipsometer. GaP thin film with very high refractive index (n=3.45 at 633 nm) was obtained. The
performance of the multilayer stack as omnidirectional reflector is also reported.
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