Study On The Improvement Of Lighting Efficiency Of GaN Based Materials And The Devices By Surface Plasmons

The mechanical,chemical and photoelectric properties of GaN based ? group nitrides are excellent.They are the preferred materials to fabricate light emitting diode(LED),laser diode(LD)and photoelectric detector.But,a series of problems such as crystal defect,quantum confined stark effect(QCSE)and droop effect still exist at present,which result in the lighting efficiency of devices not ideal.Surface plasmons(SPs)can be employed to improve the internal quantum efficiency(IQE)and light extraction efficiency at the same time.In this thesis,we prepared kinds of GaN based materials and devices with different structures by MOCVD technique.Aimed at the feature of the materials and devices,we use different SPs mode generated by different metal structures to improve their lighting efficiency.The concrete research contents are as follows.1.IBD technique and annealing process are employed to fabricate Ag nanoparticles.The influence of different fabricate conditions on the morphology and characteristic of Ag nanoparticles have been detail studied.Moreover,we also analyzed the ability of oxidation resistance of Ag nanoparticles.The research of this part lay the fundation of the Ag nanoparticles applied to improve the lighting efficiency of GaN based materials and devices.2.Ga-faced GaN based blue multiple quantum wells(MQWs)and LED were epitaxial growth on c-face double polished sapphire.Firstly,we researched the influence of surface plasmons polaritons(SPPs)and localized surface plasmons(LSPs)on the photoluminescence(PL)efficiency of the blue MQWs.The results show that SPPs generated on Ag thin film can't improve the lighting efficiency of MQWs effectively.But,fabricating Ag nanoparticles with proper size on the surface of MQWs can make the lighting efficiency be improved come true.For the sample with Ag deposition time of 35 s,the PL integrated intensity is enhanced 1.72 times.We also found that the Ag nanoparticles with bigger aspect ratio and its absorption spectrum overlap PL spectrum of MQWs more can better enhance the PL intensity of In GaN/GaN MQWs.Moreover,we put forward using thin induced polarization doped Al GaN served as the p-zone of blue LED innovatively.The structure allows Ag nanoparticles fabricated on the surface of LED,and let secondary epitaxy avoided.Meanwhile,it's benefit to realize the enhancement of light intensity of LED by localized surface plasmons method.3.N-faced GaN based purple LED was epitaxial growth on c-face double polished sapphire.In this part,we using SPs method cooperated with surface roughing to enhance the light intensity of LED.Finally,the PL intensity of the sample which was etched for 60 min and then deposited Ag for 50 nm is enhanced about 4 times.4.Ga-faced GaN based ultraviolet MQWs was epitaxial growth on c-face double polished sapphire.Firstly,we studied the influence of SPPs generate on Al film on the lighting efficiency of the MQWs.The results show that the energy carried by SPPs can't be emitted effectively by the flat Al film.That is to say,this method go against the PL enhancement.Then,we studied the influence of quadrupole plasmons on the PL efficiency of ultraviolet MQWs.The results show that the quadrupole plasmons absorbance peak of Ag nanoparticles with bigger size are stronger.And lead to the stronger coupling between quadrupole plasmons and exctions in MQWs,which contribute to the light enhancement of MQWs.Finally,we found that with the increase of spacer thickness the coupling strength between quadrupole plasmons and exctions decrease in the form of exponent.