| Summary: | 碩士 === 龍華科技大學 === 工程技術研究所 === 97 === In this study, a unique fabrication technique, with combination of hot-wall low pressure chemical vapor deposition (LPCVD), sputtering of buffer layers, and RF plasma surface treatment experiment, was developed and used to produce zinc oxide films with outstanding optronic properties. Three sets of experiments were performed; solely CVD, plasma treatment of substrates before CVD, or treatment of deposited layers after CVD. Fluorescence spectroscopy (PL), X-ray diffractometry (XRD), atomic force microscope (AFM), and scanning electron microscopy (SEM) were used to analyze samples.
The PL analysis results show that, as compared with solely CVD, surface modification after CVD has been confirmed to be a very effective way to improve the near band edge emission PL line near 380 nm. Some post CVD treated samples have PL peak intensity 30 times stronger than samples with no treatment. Actually, for almost all samples, with the oxygen concentration in CVD chamber from 10% to 90%, it was found out that plasma modification may increase the PL peak intensity for several orders of magnitude. For all plasma treated CVD samples tested, samples deposited with an oxygen content of 70% give the best results. On the other hand, XRD analysis shows these samples are nearly all (002) preferential oriented ZnO poly-crystals. For samples with treatment after CVD, the XRD peak intensity reduces, seemingly due to sputtering effect from Ar ions in plasma. SEM images show that, after treatment, the grain size of CVD ZnO solid remains unchanged, but the density decreases. No significant effect was observed on the grain size and shape. AFM shows, after treatment, surface roughness are reduced, giving a more flat surface.
As regarding to PL studies for semiconductor materials, since the photon escape depth is limited, PL has been regarded as surface phenomena. However, the effective region for plasma treatment is also just only a few nm thick. It was proposed that this is the reason why plasma treated CVD films can achieve better light-emitting PL efficiency.
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