Luminescence Enhancement Of Green Light-emitting Diodes By Surface Plasmon

Since gallium nitride (GaN) materials appeared in1990s, tremendous progresshas been made in the fabrication techniques of InGaN/GaN multiple quantum-well(MQW) light-emitting diodes (LED). It has been attracted interest for variousapplications, such as backlights of mobile phones and liquid crystal displays, LEDsigns and displays, traffic signal lamps, and indoor/outdoor lighting. AlthoughIII-nitride-based LED is already commercially available, the luminous efficiency ofblue and green LED is low. In recent years, people have been committied to improvethe luminous efficiency of blue and green LED. Many methods have been found toimprove the luminous efficiency of blue and green LED by theoretical calculationsand experimental studies. Enhanced the luminous efficiency of blue and green LEDby surface plasmon is a hot research in recent years.In this dissertation, Au nanoparticles were fabricated and the factors that affectits morphology and surface plasmon resonance (SPR) properties were studied. Thenthe luminescence of green LED was enhanced by coupling with Au nanoparticles. Wealso study the influence of different method of thermal annealing, different thermalannealing temperature and different thickness of Au film on the shape and size of Aunanoparticles and SPR. The main contents of this dissertation were organised asfollowing:(1) The choice of metal structure and materialsThe characteristics and preparation process of metal grating and sphericalnanoparticles were studied. Spherical nanoparticles can excitated the SP and thepreparation process is simple, so the luminescence of green LED can be enhanced byspherical nanoparticles. We studied the influence of the transmissivity and reflectivityof metal, the distance between luminescence center and metal structure, the distancebetween the metal surface plasmon resonance band and the peak of luminescencecenter on luminescence enhancement of green LED. Surface plasmon resonancewavelength of Au nanostructures is close to the emission wavelength of green LED.The Au nanostructures can effectively enhance the luminescence of green LED.(2) Preparation process of Au nanoparticles and the factors that affect its morphology and surface plasmon resonanceAu nanoparticles were prepared by sputtering and studied the influence ofdifferent method of thermal annealing, different thermal annealing temperature anddifferent sputtering time of Au film on the shape and size of Au nanoparticles andSPR. Two methods were used test transmission and reflection spectrum of the samplesand compared the influnce of different methods on surface plasmon resonancewavelength. Different method of thermal annealing and different thermal annealingcondition changed the shape and size of Au nanoparticles and then tuned the surfaceplasmon resonance wavelength. Different test methods only affect the strength ofextinction spectra, does not affect the surface plasmon resonance wavelength.(3) Fabrication and investigation of the green LEDs with surface plasmonGreen LEDs with surface plasmon were fabricated successfully and analyzed theoptical and electrical properties. It is noticed that a30%enhancement in opticaloutput power of green LEDs is achieved at an injection current of20mA compared tothat of LEDs without Au nanoparticles. The forward voltage of LEDs with Aunanoparticles is lower than that of LEDs without Au nanoparticles. Preparationprocess of LEDs with surface plasmon is simple and the optical output power ofLEDs can significantly improve.