| 摘要: | 本研究探討論氧化鋅奈米柱在高溫、含氫環境下的穩定性。氧化鋅奈米柱可作為氮化鎵在矽基板上的磊晶緩衝層，能有效減緩氮化鎵與矽基板之間的晶格應力，且奈米柱可用低溫、大面積的水熱法生長而成。此外，氧化鋅奈米柱的鋅在高溫製程時會擴散至氮化鎵，產生氮化鎵的鋅摻雜，形成p型氮化鎵，我們希望以此p-side-down的LED結構，來提升量子井的發光效率。
然而，在有機金屬化學氣相的磊晶過程中，基板溫度通常超過1000 ºC，且需要含氫氣的環境，這些條件會對氧化鋅產生蝕刻的作用，影響氧化鋅的晶格結構，因此氧化鋅的穩定性對氮化鎵的品質有關鍵性的影響。本研究使用快速熱退火爐管，觀察氧化鋅在高溫、不同氫含量下(空氣、真空及氮氣)的反應，希望能藉此了解氧化鋅奈米柱在氮化鎵磊晶過程中的結構變化。
根據SEM及XRD的觀察，在空氣中的氧化鋅奈米柱的耐熱程度最低，在900 ºC時就會產生形變，且與相鄰的奈米柱接合，無法保持住本身奈米柱的型態，當溫度到達1000 ºC時，奈米柱即完全塌陷；真空環境下的氧化鋅奈米柱則是在900 ºC時產生些微的形變，但還能保持奈米柱的原始型態；氮氣環境下的氧化鋅奈米柱在1000 ºC時才開始發生形變。這樣的實驗結果可以確認氧化鋅奈米柱在高溫下的不穩定性，除了氧化鋅的熱分解，在含有氫氣的環境下，還會有氫氣蝕刻的影響，造成氧化鋅奈米柱的耐熱程度更低。
;In this study, we investigated the stability of ZnO nanorods at high temperature and hydrogen environments. ZnO nanorods are employed as the buffer structure for the growth of GaN on silicon substrates via metal-organic chemical vapor deposition (MOCVD). The nanorods can be attained with a hydrothermal synthesis, which is a low-temperature and wafer-scale process. GaN grown on ZnO is inherently p-type, which is due to the diffusion of Zn ions. For LEDs, the inherent p-type GaN can benefit the internal quantum efficiency by forming the p-side-down structure, which reverses the polarization-induced field and increases carrier injection efficiency.
However, during MOCVD growth, the substrate temperature usually exceeds 1000 ºC, and a hydrogen-containing atmosphere is required, and these conditions can lead to thermal decomposition and H2 back-etching of ZnO nanorods, sacrificing the crystal qualities of GaN-on-Si. To understand the etching and decomposition process, rapid thermal annealing (RTA) with different hydrogen contents (air, vacuum, and nitrogen) was used to treat ZnO nanorods.
According to the observations with scanning electron microscopy and X-ray diffraction, it is found that the ZnO nanorods in air start to deform and decompose at 900 ºC, and completely collapse at 1000 º C. In the vacuum environment, the nanorods slightly deform at 900 ºC, but the original “rod” shape can be maintained. The ZnO nanorods are most durable in nitrogen, and the geometry is well maintained until the temperature reaches 1000 ºC. These results confirm that, in addition to thermal decomposition, ZnO nanorods suffer H2 back-etching in the presence of high-temperature hydrogen, which should be closely cared during the growth of GaN-on-Si. |
