| dc.description.abstract | 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. ?
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