Metallic Localized Surface Plasmon Enhanced Near UV-emissions From Semiconductors

Solid state lighting, in which light emitting diodes (LEDs) are used, and leads to the third revolution of the human illuminative realm by means of the advantages of saving energy, environmental protection and long lifespan, etc. The combination of yellow phosphor irradiated by a blue InGaN LED is the common way to realize white light emission in industry, but with a poor color-rendering-index. In order to achieve high color-rendering-index, the near-UV LEDs have been extensively investigated. However, the synthesized white light using the near UV irradiation and RGB phosphors has a primary drawback of low efficiencies. In this study, I try to improve the efficiency of UV emissions by fabricating high quality multi-quantum wells and ZnO films and coupling with metallic surface plasmons using the following methods.1. By numerical calculation, I found investigated that the frequency and intensity of localized surface plasmon resonance (LSPR) are highly dependent on the size, shape of the nanoparticles (NPs) and the surrounding dielectric medium. In NPs arrays, the LSPR of NPs leads to very large enhancements of electromagnetic field. The finite difference time domain (FDTD) simulation shows that the LSPR peak positions of the Pt NPs and the Al NPs with a size of100nm are350and380nm, respectively, and the maximum electric field enhancement (about30times) is around the sharp tips of squares and triangles.2. The Pt and Al NPs arrays with different sizes and shapes were fabricated by thermal annealing, electron beam lithography (EBL) and focus ion beam (FIB). In order to get sharp-edged NPs, the minimum size of NPs was100nm using EBL and the minimum size of NPs was50nm using FIB.3. Nonploar m-plane ZnO films was successfully grown on Si substrates at a relative low temperature of200oC by using atomic layer deposition (ALD). Deep level emissions due to zinc interstices or oxygen vacancies were very weak. Well defined NP arrays with different shapes were fabricated on the surface of ZnO by EBL. By top excitation of the Al NP arrays coupled with ZnO, a2.6-fold enhancement of the square NPs in peak photoluminescence intensity was achieved.4. InGaN/AlGaN multi-quantum wells (MQWs) were grown on sapphire substrates by radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE). The structural and optical properities of the MQWs were studied by using transmission electron microscopy (TEM) and photoluminescence (PL). The Pt NPs arrays with a diameter of 100nm were deposited on the top of the MQWs, and the coupling between the near-UV MQWs and LSPR was investigated for the first time.5. In order to understand the shape-dependent enhancements and the coupling mechanism, the time-resolved PL spectra and the temperature-dependent PL spectra were measured. Compare with the electric filed intensity of the surface, we can conclude that the local electric field enhancement and the increasing radiative decay rate made the dominant contributions to improve the band-edge luminescence.