| Summary: | 碩士 === 國立成功大學 === 微電子工程研究所碩博士班 === 94 === For recent years, many researches have been published in red RCLED, but few papers have been published on GaN based RCLED. The main reason is the difficulty of growing structures. If the multilayer materials of AlGaN and GaN were used to from the DBR in the GaN based RCLED structure. We can increase the mole of Al or increase the AlGaN/GaN pairs to increase the reflectivity of the DBR. However, it has a problem of lattice mismatch between AlGaN and GaN. If we increase the mole of Al or increase the AlGaN/GaN pairs, it will generate cracks in the films. Therefore, we can not obtain the high quality and high reflectivity of the DBR. We will choose two materials of dielectric that have large difference of refractive index to replace the AlGaN/GaN to form high quality DBR. In this thesis, we used the multilayer material of TiO2/SiO2 as the external DBR in the GaN based RCLED. However, in this design, the substrate must be removed or thinned to deposit the DBR at the two sides of GaN based RCLED structure.
Firstly, the laser will be used to remove the sapphire. The reactive ion etching will be used to remove the buffer layer to the n-type GaN layer. We will also use the chemical mechanical polishing to improve the roughness of the n-type GaN surface.
In this thesis, we fabricated the GaN based LED with and without the multilayer material of TiO2/SiO2 as the external DBR. We also measured the performance of the traditional LED (without external DBR) and the RCLDE (with external DBR). The threshold voltage of the RCLED is 3.7V at the operating current of 20mA. The FWHM decrease from 17.2nm to 10nm where peak is at 450nm.
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