Preparation And Optical Properties Of InGaN/GaN-based Nanopillar LEDs

GaN and its alloy compounds(InGaN,AlGaN,etc.)are representative of ?-?compound semiconductor materials,and since group ? nitride semiconductor materials are direct-gap semiconductors and have a wide variation in the bandgap width,the bandgap variation range From 0.7 eV in InN to 6.28 eV in AIN,the corresponding energy can be covered from near-infrared to deep ultraviolet,coupled with its excellent thermal stability and excellent electro-thermodynamic properties,it is widely used in the fields of luminescence,display,detection and storage application.Especially in terms of optoelectronic devices,InGaN alloys play an irreplaceable role as an important luminescent material.Although the characteristics and applications of InGaN/GaN MQW LEDs have made great progress and development in the past,there are still many problems to be solved.One of the most important issues is that the luminous efficiency of InGaN/GaN MQW LEDs is still relatively low.In this dissertation,the strong phase separation InGaN/GaN MQWs LED with c-plane sapphire substrate was grown prepared by metalorganic chemical vapor deposition(MOCVD).On this basis,the nanopillars LED was prepared by ICP dry etching.The PL,Raman,SEM and Rsoft simulations were used to investigate the effects of nanopillars structures on the optoelectronic characteristics and internal physical mechanisms of InGaN/GaN-based LEDs.The main contents are as follows:(1)Compare the luminous intensity and luminous efficiency of the original LED(planar sample)and the nanopillars arrays LED sample(nanopillars sample).By contrast,we found that after the planar sample was etched,the luminescence intensity of the sample was significantly enhanced.The PL intensity of the nanopillars sample was 1.05-3.56 times stronger than the planar enhancement.The strain relaxation of the nanopillars sample results in the weakening of the QCSE,the probability of overlapping of wave functions of electrons and holes is larger,and increase of the internal quantum efficiency.The large specific surface area and light-guiding effect of the nanopillars LED increases the light extraction efficiency,which can be quantitatively verified by Rsoft simulation experiments.(2)HRTEM,SEM and Raman spectra of planar and nanopillars samples were analysed.HRTEM spectra revealed that the In-riching of InGaN matrix in the MQWs layer resulted in the strong phase separation of the QDs,The quantum dots and the InGaN matrix correspond to two emission peaks of 2.3 eV and 2.6 eV in the PL spectra.The SEM spectrum can visually see the regularly arranged nanopillars array structure,Raman spectroscopy finds that the E2(H)phonon model of the nanopillars structure is blue-shifted in the low frequency direction and proves the strain relaxation of the InGaN/GaN nanopillars LED.(3)The localisation effect changes in samples before and after etching were studied.The PL spectra of planar samples and nanopillars samples with temperature dependence and excitation power dependence have been found that the localisation effect both in the InGaN matrix and in the QD regions are enhanced.The mechanism responsible for the enhancement of the strain relaxation-induced carrier localisationeffect after etching,is explained by the supposed schematic diagrams indicating the possible mechanism of carrier transfer and distribution in two different QWs.(4)The luminous efficiency and radiation field of planar samples and nanopillars samples were compared.The FDTD algorithm simulation software was used to simulate the light extraction efficiency,electromagnetic field distribution,far field distribution and other properties of planar samples and nanopillars LEDs.Theintegration analysis and comparison with the experimental data demonstrated the remarkable effect on the improvement of luminous efficiency provides theoretical support for experimental data.