摘要
本論文主要是探討氮化鎵奈米線(Gallium Nitride nanowires)半導體的光學性質。利用Vapor – Liquid – Solid合成的方法，從電子顯微鏡中可以觀察到大量的直徑範圍約20 nm-200 nm（平均為50nm），且其長度達數個微米(μm)尺度的氮化鎵奈米線晶體。此種簡單又可大量製造的方法，有助於高效率光電元件的應用。為了了解這種氮化鎵奈米線的物理特性，我們做了一系列的光學性質測量。 經由X光粉末繞射實驗，發現氮化鎵奈米線晶體為hexagonal wurtzite結構。利用改變溫度與不同激發功率的條件下，觀察光激螢光光譜。除了wurtzite結構的band-edge emission被量測到能量為3.471 eV，我們也發現出現在能量為3.272 eV的放射波峰，位置剛好對應在閃鋅礦結構的位置上，此外也測量到半高寬較為寬廣的黃光放射，能量大約在2.4 eV。利用變溫的光激螢光實驗，我們也觀測到donor-acceptor pair躍遷機制出現，其能量在3.080 eV。最後，經過變溫的光激螢光光譜實驗，發現我們的樣品對於溫度的影響很小，這樣的特性正好符合光電元件所需要的穩定性。 我們也利用拉慢散射光譜實驗，檢測我們所合成出來的氮化鎵奈米線晶體。我們發現樣品有兩種效應。一個是有效尺寸限制效應，另一個是表面無序的效應，那是由於我們從光譜上發現A1 (LO) phonon mode有不對稱的線形、zone- boundary phonons 、 vibrational modes of vacancy-related defects的出現，所得到的估計。我們也利用高斯函數局限公式來估計氮化鎵奈米線的直徑寬度，發現與SEM和TEM的觀察結果互相符合。最後，利用不同溫度、氣體，經過熱退火處理之後的樣品，分別比較其拉曼散射與光激螢光實驗，發現於拉曼散射光譜顯現出因為樣品缺陷所活化的670 (1/cm) mode，和從光激螢光光譜被加強的藍色螢光帶有直接的關係。
並列摘要
Nanostructures present new and particularly interesting phenomena mainly related to the strong modifications of the fundamental physical properties of the material, due to confinement in the three dimensions space. Developing an understanding of the fundamental physical properties is therefore crucial for realizing their potential applications. In this study, we report the study on the physical properties of large-scale GaN nanowires, grown by the vapor-liquid-solid (VLS) mechanism on Si (100) substrates. The VLS synthetic technique, which makes possible simple and large-scale production of GaN nanowires, opens up applications of the nanowires for high efficiency optoelectronics devices. The GaN nanowires had the wurtzite structure as characterized using photoluminescence (PL), Raman scattering, X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) measurements. These results are presented in the following parts. We first discuss photoluminescent properties of GaN nanowires. The scanning electron microscopy and the TEM show that almost all the resulting materials exhibit wire-like structures with diameters in a range from 20 to 200 nm and lengths up to several micrometers. The GaN sample were carried out and characterized by temperature and powder dependent photoluminescence experiment. In addition to the band-edge emission at 3.471 eV due to h-GaN, we have observed a weak feature around 3.272 eV corresponding to the emission of c-GaN and yellow emission at 2.4 eV. We suggest that the 3.080 eV line arises from donor-acceptor pair. Through the temperature dependence, we have showed that the emission of GaN nanowires is very resistant to the change of temperature. This behavior is beneficial for the stability of GaN used in optoelectronic devices. We then report a study on the Raman spectra of GaN nanowire grown on Si (100) by the vapor-liquid-solid method. The effects of finite size confinement and surface disorder were observed including asymmetric lineshape, zone-boundary phonons and vibrational modes of vacancy-related defects. Our Raman spectra can be well described by the Gaussian confinement model, and the nanowire diameter obtained from the best fit is in good agreement with the value estimated using scanning electron microscope. Moreover, through the annealing process, we identify that the 670 (1/cm) peak is activated by defects. This result is well correlated with the appearance of blue band luminescence.
參考文獻
延伸閱讀
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