| Summary: | 碩士 === 國立交通大學 === 電子物理系所 === 102 === In this thesis, we use Metalorganic Chemical Vapor Deposition (MOCVD) reactor to growth GaN epilayer. We insert SiN layer before main eplayer, and by varying SiH4 flow rate, we can control SiN coverage condition and the growth mode of GaN on top of it. We then perform Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD) and Photoluminescence (PL) experiments.
From SEM result, we know that the SiN coverage condition will affect GaN island density on top of SiN, which led to uncoalescence surface when flow rate as high as 80nmol/min. We calculate dislocation density from XRD result, and a-type dislocation density decrease with increasing SiH4 flow rate until the film can’t coalescence (From 8×108 cm-2 to 2×108 cm-2), then it increase again. The reason is dislocation bending during 3D growth, it increase the probability of dislocation reaction and annihilation, but when the film fail to coalescence, this mechanism is hindered, so the dislocation density rise again. In the end, the PL result shows up to 4x intensity increase by reducing dislocation density from 8×108 cm-2 to 2×108 cm-2.
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