| Summary: | 碩士 === 國立中央大學 === 光電科學與工程學系 === 105 === In recent years, the growth of GaN-on-silicon has attracted much research interests because of its low cost. However, some issues remain to be solved: (1) There is a large lattice mismatch between GaN and silicon, and this leads to high density of crystal defects, reducing the electron mobility in transistors. In addition, the defects also hamper the quantum efficiencies of LEDs and solar cells; (2) The huge mismatch in thermal expansion mismatch between the two materials even causes cracks, making epilayers unsuitable for device fabrication.
To address the issues, we adopted low-temperature AlN as the nucleation layer for the growth of GaN-on-Si. The low-temperature AlN not only provides the nucleation seeds for the subsequent GaN growth, but also prevent the thermo-decomposition of the impurities formed on the reactor wall. The low-temperature AlN buffer is followed by a AlN/AlGaN layer grown at varied temperatures to release the lattice strain. We found the substrate temperature of the AlN/AlGaN strain-engineering layer plays a decisive role in the surface morphology of subsequent GaN layer. Details characterization results and discussions will be presented.
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