近年來，氮化鎵成長於矽基板對於製作光電半導體元件是個非常重要的技術，然而氮化鎵成長於矽基板面臨了幾個重大的問題，其一為氮化鎵跟矽基板的晶格差異過大，導致磊晶完成後氮化鎵內部會含有大量的缺陷，而這些缺陷對高電子遷移率電晶體來說會降低電子在二維電子氣內的遷移率，此外缺陷也會降低發光二極體及太陽能電池的效率；其二為氮化鎵跟矽基板之間的熱膨脹係數差異過大，在磊晶過程升降溫中會導致基板彎曲最終氮化鎵會發生龜裂，影響之後原件的製程。 為了提升氮化鎵半導體於矽基板上的磊晶品質，本研究探討基板溫度對氮化鎵表面平整度的影響。我們先以低溫的氮化鋁薄膜作為磊晶成核層，以幫助氮化鎵在高溫時的橫向癒合。使用低溫的目的，是要避免腔體表面的氮化物雜質裂解，因而污染矽基板與氮化鎵的界面。成核層完成後，再以高、低溫交錯的方式，成長氮化鋁與氮化鋁鎵，作為氮化鎵的應力緩衝層。我們發現，氮化鋁/氮化鋁鎵應力緩衝層的磊晶溫度，對氮化鎵的晶格癒合與最終的表面平整度，有很密切的關聯。 ;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.
