以有機金屬化學氣相沉積法成長用於深紫外光發光二極體的高品質氮化鋁與氮化硼;High quality AlN and BN grown by MOCVD for deep UV LEDs

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题名:	以有機金屬化學氣相沉積法成長用於深紫外光發光二極體的高品質氮化鋁與氮化硼;High quality AlN and BN grown by MOCVD for deep UV LEDs
作者:	黃竣彬;Huang, Chun-Pin
贡献者:	光電科學與工程學系
关键词:	氮化鋁;氮化硼;有機金屬氣相沉積法;AlN;BN;MOCVD
日期:	2020-05-15
上传时间:	2020-06-05 17:13:09 (UTC+8)
出版者:	國立中央大學
摘要:	本篇論文描述以有機金屬化學氣相沉積的生長方法提升深紫外光發光二極體關鍵材料的晶格品質。這些方法包括應用於高品質氮化鋁的氣流中斷法和應用於氮化硼窗口層的調降五三比。尤其，氫氣流對於氮化鋁和氮化硼成長是不可或缺的。因為它不僅抑制有機金屬源與氨氣間的氣相預反應，還能去除晶膜表面的點缺陷。為了在不犧牲晶格品質的前提下，縮短深紫外光發光二極體的磊晶時間，尤其在基板溫度低於1200℃時，前趨源脈衝流動是有效的方法之一。為達成此目標，我們以1180℃的單一基板溫度，並利用脈衝氨氣流的方式，成長厚度達1.5 μm的氮化鋁單晶層。該氮化鋁磊晶層具備平滑表面以及半高寬427弧秒的X光於(102)面繞射峰。為了近一步縮短氮化鋁層的生長時間，我們使用氨氣與三甲基鋁的雙脈衝氣流，再加上氫氣脈衝蝕刻製程來控制成核島丘晶粒尺寸。在厚度為1.5 μm 的氮化鋁磊晶層表面上，我們得到的方均根粗糙度低達0.25 nm (量測面積: 5x5 μm2)。這些成果顯示: 脈衝氣流的蝕刻效應，能將氮化鋁的磊晶模式從三維的島狀結構，轉變成二維的層狀結構。本研究的最後一個項目，是要闡明氮化硼層在氮化鋁表面的成長機制。氮化硼層被預期可取代超高電阻率的p型氮化鋁鎵層。根據X光繞射儀、穿透式電子顯微鏡和電子能量損失譜的結果，我們確認氮化硼層從方形到菱形體的晶體轉變，也發現:氮化硼適合在低五三比的氣流環境中成長，因為當五三比降低時，氫氣更能抑制氣相預反應，並催化從方形晶格到菱形晶格的轉變。總的來說，氮化硼的磊晶過程歸納如下：氫氣流抑制氣相預反應 → 方形氮化硼成核層 → 晶體轉變 → 菱形氮化硼連續生長。 ;This dissertation describes the growth methods of metal-organic chemical vapor deposition (MOCVD) to enhance crystal qualities of the key materials in deep ultraviolet light-emitting diodes (DUV LEDs). The methods include pulsed flow for high-quality AlN buffer and reduced V/III ratio for BN window layer. Specifically, H2 flow is essential for the growth of AlN and BN, as it not only suppresses the gas-phase pre-reaction between metal-organic source and NH3 but also etches the point defects on the epitaxial surface. To shorten the growth time of DUV LEDs without sacrificing crystal qualities, pulsed-flow of precursors is one of the most effective way, particularly at the substrate temperature below 1200℃. In this regard, a 1.5-μm AlN buffer containing two pulsed-NH3-flow AlN layers was attained at a single substrate temperature of 1180 °C. The AlN buffer exhibits atomically flat surface and the x-ray diffraction (XRD) (102) peak width of 427 arcsec. To further shorten the AlN-buffer growth, a double-pulsed-flow of NH3 and trimethylaluminum (TMA) and pulsed-H2 etching process were used to control the grain size of nucleation islands. The 1.5-μm-thick AlN epilayer exhibits a root-mean-square surface roughness of 0.25 nm (scanned area: 5x5 μm2). The pulsed etching technique facilitates the crystal transformation of AlN from three-dimensional (3D) nucleation to two-dimensional (2D) layer-by-layer growth. The last part of this work aims to clarify the growth mechanism of BN on AlN. The BN layer is to replace the resistive p-type AlGaN for DUV LEDs. The lattice transformation of BN from cubic (cBN) to rhombohedral (rBN) structure was confirmed with the results of XRD, transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). According to the cross-sectional TEM images, the BN growth favors low V/III ratios so that H2 gas can effectively suppress the gas phase pre-reaction and catalyze the crystal transformation from small cBN nano-islands to rBN monolayer. The growth of BN is summarized as follows: H2 flow suppressing gas-phase pre-reaction → cBN nucleation layers → crystal transformation → rBN continuous growth.
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