氮化物奈米結構的穿透式電子顯微研究

Abstract

在本論文中，首先我們報告於利用有機金屬氣相沉積技術利用氣態-液態-固態長晶模式在c平面藍寶石基板上的氮化鎵層上成長氮化銦鎵奈米柱。在氣態-液態-固態長晶模式下，我們使用金的奈米顆粒當作催化劑，而奈米金顆粒係在氮化鎵層上面以高功率雷射照射金薄層產生。氮化銦鎵奈米柱成長後，我們使用穿透式電子顯微鏡的能量散佈能譜儀及高角度環形暗場像觀察到氮化銦鎵奈米柱的螺旋式沉積結構，接下來，我們在垂直於氮化銦鎵奈米柱c軸平面上得到銦成份的變化，且在長晶的方向觀察到準週期性銦成份的變化，這乃由於沉積過程中銦的過飽和所造成，氮化銦鎵奈米柱的螺旋式沉積是由於在氮化鎵基板上之螺旋式差排所造成的。 另外，我們於規則排列的氮化鎵奈米柱上使用不同溫度、不同時間及不同銦的流量來成長氮化銦鎵/氮化鎵量子井結構，我們使用陰極射線致發螢光光譜來比較奈米柱頂端形成具極性的c平面圓盤狀量子井結構以及奈米柱側壁形成非極性的m平面量子井結構發光波長的變化，可以觀察隨著量子井沉積時間之增加、沉積量子井的溫度的下降、以及沉積量子井時銦的流量之增大都會使陰極射線致發螢光波長變長，隨著陰極射線致發螢光波長變長時，c平面量子井結構以及奈米柱側壁的m平面量子井結構發光波長的差異性變小，同時不同高度側壁的m平面量子井發光波長的變化幅度愈大，另外我們使用穿透式電子顯微鏡影像的應力分析，我們可以得到兩組量子井的平均寬度及平均銦含量，頂面的c平面量子井寬度比側壁的m平面量子井寬度大很多，然而c平面量子井銦含量比側壁的m平面量子井銦的含量略少，在側壁的m平面量子井的寬度與銦的含量隨氮化鎵奈米柱側壁高度增大而增加，應力分析的量子井平均寬度及平均銦含量的變化趨勢與陰極射線致發螢光波長變化相符合。

In this dissertation, first the spiral deposition of InGaN with a quasiperiodical distribution of indium content along the growth direction for forming InGaN nanoneedles (NNs) with the vapor-liquid-solid (VLS) growth mode is demonstrated. The VLS growth is implemented by using Au nanoparticles (NPs) as the catalyst in metalorganic chemical vapor deposition. The Au NPs on a GaN template are generated through pulsed laser irradiation. The observation of spiral deposition is based on the analyses of the scanning results in the high angle annular dark field and energy dispersive X-ray measurements of transmission electron microscopy. In the measurements, the composition variations along and perpendicular to the growth direction (the c-axis) are illustrated. The alternating indium content along the growth direction is attributed to a quasiperiodically pulsed behavior of indium supersaturation process in the melted Au NP at the top of an InGaN NN. The spiral deposition of InGaN is due to the formation of an NN at the location of an Au NP with a screw-type dislocation beneath in the GaN template, at which the growth of a quasi-one-dimensional structure can be easily initiated. Regularly patterned InGaN/GaN quantum-well (QW) nanorod (NR) arrays are grown under various growth conditions of indium supply rate, QW growth temperature, and QW growth time for comparing their emission wavelength variations from the top-face c-plane and sidewall m-plane QWs based on the cathodoluminescence (CL) measurements. Generally, by increasing indium supply rate, decreasing QW growth temperature, and increasing QW growth time, the emission wavelength becomes longer. With longer emission wavelengths, the difference of emission wavelength between the top-face and sidewall QWs is smaller. Meanwhile, the variation range of the emission wavelength of the sidewall QWs over the different heights on the sidewall becomes larger. Strain state analysis based on transmission electron microscopy is undertaken to calibrate the average QW widths and average indium contents of the two groups of QW. The QW widths of the top-face QWs are significantly larger than those of the sidewall QWs. However, the indium contents of the top-face QWs are smaller than those of the sidewall QWs. On the sidewall, both QW width and indium content increase with height. The variation trends of the calibrated QW widths and indium contents are consistent with those of the CL emission wavelengths.