本篇論文以溶膠－凝膠法製備Mg2TiO4薄膜，並且使用旋轉塗佈方式沉積於p-type Si(111)基板上，選用鋁(Al)作為上電極，形成金屬/氧化層/半導體(MOS)電容結構，探討不同薄膜退火溫度下，介電薄膜的物理特性、電特性。隨後去比較不同退火條件下光致螢光特性方面的差異，並推測其可能原因。實驗結果顯示，隨著退火溫度從700℃增加到900℃，由XRD可看出首先在700℃ Mg2TiO4薄膜幾乎為非晶，直到退火800℃才有明顯的Mg2TiO4結晶相，當溫度升高到900℃後則出現MgTiO3的二次相。再從SEM發現表面型態由700℃到900℃退火，晶粒大小有成長的趨勢，到退火900℃後則發現表面有多處區塊突起。推測在退火900℃時基板和薄膜接面有嚴重的擴散，並輔以高解析電子能譜儀(XPS)得到佐證。電性方面，比較不同退火溫度下，發現薄膜退火800℃的漏電流為10-7J(A/cm2)~10-8J(A/cm2)和電容值(950pF)，並經由平板電容公式計算結果，可得到在100kHz下k值在12左右。光學特性方面，首先從光致螢光光譜可發現退火700℃增加到800℃，波長700nm到750nm區段光致螢光有明顯增強，退火900℃後光致螢光減弱，退火1000℃後光致螢光幾乎不太明顯，接著比較在不同氧氣含量下退火(O2、vacuum) 光致螢光光譜，發現到氧氣有明顯光致螢光，真空則變得很微弱，綜合一些分析發現結晶性可能會影響光致螢光強度，而氧空缺會抑制光至螢光強度，最後我們推測在700nm到750nm區段光致螢光原因可能為Mg2TiO4薄膜本質結構上的缺陷所產生，因此選擇適當的結晶溫度與在氧氣下退火可以改善Mg2TiO4薄膜發光特性。

In this study, Mg2TiO4 thin films were deposited on p-type Si(111) substrate by the sol-gel process. Firstly, the Mg2TiO4 thin films’ structural, optical and electrical properties were characterized at different annealing temperatures using x-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), conductivity measurements and photoluminescence (PL). Experimental results indicate that the Mg2TiO4 thin films crystallized at the annealing temperature of 800℃, and the interface between the thin films and substrate began diffusing at an annealing temperature of 900℃. The interface diffusion apparently influenced the thin films’ structural, optical and electrical properties Hence, we obtained the best properties at an 800℃annealing temperature, at which point the leakage current was 10-7J(A/cm2)~10-8J(A/cm2), the dielectric constant was approximately 12, and the photoluminescence had a strong intensity at the 700nm-750nm wavelength.
Secondly, we introduced different atmospheres (Air、O2、N2、N2/H2、vacuum) when annealing, and then compared the influence of these atmospheres on photoluminescence. It was found that the O2 atmosphere had the strongest intensity, while the N2/H2 atmosphere had the weakest. Consequently, we suspect that the oxygen vacancy may suppress Mg2TiO4 thin film photoluminescence intensity. Ultimately, we found that choosing an appropriate crystallizing and annealing temperature in an O2 atmosphere can achieve strong photoluminescence intensity for Mg2TiO4thin films.

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