Surface Plasmon Enhanced Electroluminescence Of ZnO-Based Devices

Ultraviolet light emitting devices (LEDs) and lasing diodes (LDs) hold thepromise for a variety of applications including solid state lighting, high-resolutionphotolithography, high density data-storage, and biomedical analysis, etc. Zinc oxide(ZnO), with a direct wide band gap (3.37eV) and a lager exciton binding energy (60meV), is a promising candidate for ultraviolet LEDs and low-threshold LDs.Although ZnO-based ultraviolet light-emitting and laser devices have been studiedextensively, the performance of such devices is still far below expectation, and toimprove the performance has been one of the key issues in ZnO-basedoptoelectronics. Surface plasmons (SPs) are coherent electron oscillations that existat the interface between any two materials where the real part of the dielectricfunction changes sign across the interface, and an efficient coupling of metal SPswith luminescent material can lead to several orders of magnitude improvement overspontaneous emission rate. There have been several reports on metal SPs enhancedphotoluminescence of ZnO, however, the report on SPs enhancedelectroluminescence (EL) is still rare. In this dissertation, SPs of noble metalnanoparticles (NPs) have been employed to enhance the EL and lasing characteristics ofZnO-based LEDs and LDs, and the following results have been achieved:(1) n-ZnO/i-ZnO/MgO/p-GaN structured LEDs have been fabricated byplasma-assisted molecular-beam epitaxy system. Ag NPs whose surface plasmon resonance absorption spectrum overlaps well with the EL of the structure wereemployed to improve the emission characteristics of the LEDs. It is found that theEL of the LED has been increased by around220%by the incorporated Agnanoparticles.(2) In order to explore the enhancement mechanism for the Ag nanoparticlesincorporated LEDs, three kinds of metal nanoparticles with different SP resonanceabsorption peaks were employed to modify the EL characteristics of then-ZnO/i-ZnO/MgO/p-GaN structured LEDs. It is found that the emission of thedevices can be enhanced at selective wavelength that matches the absorption spectraof the metal nanoparticles. The selective EL enhancement confirms that theenhancement of EL is derived from the resonant coupling between the SPs of metalNPs and the excitons in the active layer of the LEDs.(3) Electrically pumped random lasing has been realized in Au/MgO/ZnOstructures. By incorporating Ag nanoparticles, whose absorption spectrum overlapswell with the emission spectrum of the structures, the threshold of the random lasingcan be decreased from63mA to47mA. By further introducing a dielectric layerinto the structure to decrease the ohmic loss of the Ag nanoparticles, the threshold ofthe random lasing can be decreased further to21mA. The decrease in the thresholdcan also be attributed to the resonant coupling between the excitons in the activelayer and the SPs of the Ag nanoparticles.