Light-emitting diodes efficiency improvement with an AlN nanorod template and applications for Glucose-sensing

This thesis contains two research projects. First, Aluminium nitride (AlN) nanorod template was developed on the sapphire substrate by the high temperature tube furnace as a nucleation layer for the epitaxy of Gallium nitride (GaN) which leaded to the epitaxial lateral overgrowth during the process. Second, we combined the GaN-based light-emitting diode (LED) into the detection system in order to construct a glucose-sensing platform. Nowadays, about 95 % of the GaN-based LEDs are made on sapphire by metal-organic chemical vapor deposition (MOCVD). Due to the mismatch of the lattice constant and the thermal expansion coefficient, a large number of threading dislocations (TDs) are generated in the epi-layer of GaN. In order to improve the crystal quality of GaN, Vapor-liquid-solid (VLS) mechanism is used to develop AlN nanorod template on the sapphire substrate which leads to epitaxial lateral overgrowth during the process of epitaxy. From the Raman spectrum analysis, the residual stress of the sample with AlN template is reduced from 1.25 GPa to 0.78 Gpa. By transmission electron microscopy (TEM) images, we can know that the density of the TDs has been reduced. The stacking fault on the nanorod template can block the TDs from penetrating to the surface. Finally, by the temperature-dependent photoluminescence (PL) analysis, we found that the internal quantum efficiency (IQE) of MQWs is enhanced by 12%. With the development of internet of things (IoT), biosensor combined with smartphone has been a popular research. In this part of the research, we proposed an accurate and quick detection platform which included of GaN-based LED light sources for glucose-sensing. The electro-optical characteristic was first defined. The detection of different glucose solution was then conducted. With the variation of the refractive index, the propagation of the light was altered. The angular peak shift was recorded by our detector. Our system shows a good linear correlation and the bulk refractometric sensitivity is calculated to be 122.73°/RIU. By the repeatability test, our system shows a great result, showing a good stability. The photonic crystal GaN-based LED was substituted for the planar LED as a light source. The result shows that only the intensity has been enhanced while the sensitivity was not improved. Finally, the sugar content in beverage was taken into consideration and the prototype of the portable detection system model was also proposed.