本研究以濺鍍的方式，在(100)矽基板上得到60-100 nm厚的氧化鋅薄膜，作為氮化鎵在矽基板上的磊晶緩衝層。此氧化鋅薄膜能緩衝氮化鎵與矽之間的晶格差異，在理論上可提升氮化鎵磊晶層的結晶品質。根據X光繞射儀的量測結果，氧化鋅薄膜晶向為c-plane方向。氮化鎵磊晶層是以有機金屬化學氣相沉積(MOCVD)系統完成的。在磊晶過程中，重要的參數包括基板溫度、時間、壓力及氣流五三比。我們利用掃描式電子顯微鏡(SEM)以及原子力顯微鏡(AFM)來觀察磊晶表面情形，並發現濺鍍而成的氧化鋅會形成奈米柱的結構，使得氮化鎵的磊晶層表面呈現微米尺度的多晶梯型結構。 除了c-plane的氧化鋅，我們還製備m-plane的氧化鋅薄膜。m-plane氧化鋅薄膜的目的是要藉由消除量子侷限史塔克效應，來提升氮化銦鎵量子井的發光結合效率。我們發現適當的退火條件以及水熱法的再生機制，可改變氧化鋅分子堆疊的方向，因而得到m-plane的氧化鋅薄膜，而其中重要的參數包括：薄膜厚度、退火溫度、以及水熱法的環境條件。 In this research, a thin (60-100 nm) ZnO layer deposited by sputtering is employed as the buffer layer for the epitaxial growth of GaN on (100) Si substrates. The ZnO buffer mitigates the huge lattice mismatch between GaN and Si, and therefore is expected to improve the crystal qualities of GaN. The orientation of the sputtered ZnO thin film is along the c-axis according to X-ray diffraction (XRD) ω-2θ measurements. During the growth of GaN in the metal organic chemical vapor deposition (MOCVD) system, the important parameters include substrate temperature, growth duration, reactor pressure and V/III ratio. The morphology of GaN epilayers are analyzed by scanning electron microscope (SEM) and atomic force microscopy (AFM). It is found that polycrystalline GaN micro-trapezoids are formed on the ZnO buffer, which is believed to stem from the unique rod-like ZnO nanostructure produced by the sputtering process. In addition to the c-plane ZnO buffer, m-plane ZnO layer is also prepared in this project. The goal of m-plane ZnO buffer is to build nonpolar InGaN multiple quantum wells, in which the radiative recombination efficiency can be enhanced by eliminating the undesired quantum-confined Stark effect (QCSE). The m-plane ZnO layer is realized by a post-annealing at 850 °C after the sputtering process, followed by the hydrothermal regrowth of ZnO at 90 °C for 2 hours. Preliminary results show that the orientation of the ZnO layer is strongly dependent on layer thickness, post-annealing temperature, annealing environment, and the conditions of the hydrothermal regrowth.
