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標題: 奈米結晶氧化矽薄膜光激發光特性之研究
Photoluminescence from nc-SiOx:H
作者: 賴瑞豐
Lai, Jui-Feng
關鍵字: SiOx;非晶氧化矽薄膜;nc-SiOx;photoluminescence;nanocrystal silicon;奈米結晶氧化矽薄膜;光激發光;奈米結晶矽
出版社: 精密工程研究所
腔體壓力、SiH4/N2O/H2、電漿功率、toff及沉積溫度分別固定為0.3 torr、4 /12 /80 sccm、30 W、50 ms及70℃。ton的時間由2、5、12、 25、50、100、150、200、325、450、 800、1200 ms變化至連續工作(cw)。SiOx薄膜沈積厚度固定為310 nm,其矽氧鍵結由傅立葉轉換紅外線光譜(FTIR)測量。nc-SiOx薄膜的O/Si比例、結晶結構及尺寸由能量散佈光譜(EDS)、拉曼散射光譜(Raman)、X光繞射(XRD)及高解析度穿透式電子顯微鏡(HRTEM)測量及分析。
EDS量測結果顯示,在N2O/SiH4 = 3的製程反應氣體條件下,ton由5 ms變化至800 ms的時間可有效改變電漿中反應氣體解離成份將SiOx薄膜中O/Si的比例控制在0.1到0.57倍之間。FTIR量測結果顯示,各試片具有850 cm-1 (Si-O 彎折模)、1060 cm-1 (Si-O-Si 伸縮模)及2240 cm-1(H-Si-O伸縮模)三個峰值,ton = 200 ms試片(O/Si比例:0.57)的850 cm-1及2240 cm-1峰值強度介於其他試片之間,1060 cm-1峰值強度則非常接近最大值。退火處理後,nc-SiOx試片的拉曼散射光譜的背景螢光值均較退火處理前增加約1至2個數量級,且ton = 200 ms試片有最大值92倍,此結果間接指出薄膜中形成具直接輻射發光的奈米結晶矽。而XRD結果顯示,ton = 200 ms試片在 、 、 及 處,相較其他試片有明顯的結晶訊號。nc-SiOx薄膜PL光強測量結果顯示,各試片峰值位置都約在800 nm,且強度隨著O/Si比例增加而增強,ton = 200 ms有最大的O/Si比例(0.57)其發光強度最強。上述結果顯示,O/Si比例由0.1變化至0.57可以增加nc-SiOx薄膜的PL光譜強度。由於各試片之PL發光峰值變異不大,代表矽奈米結晶尺寸變化不大,造成發光強度變化主要是由於結晶比例之變化所造成。ton = 200 ms試片的HRTEM結果顯示,薄膜中大多形成約3 nm的奈米結晶矽,由其結晶顆粒分佈之面積估計其結晶比例約為33 ﹪

In this thesis, the amorphous silicon oxide (SiOx) films with various O/Si ratios were deposited by plasma-enhanced chemical vapor deposition with the pulse-modulated RF power. The influence of the pulse-on time (ton) on the O/Si ratio of the SiOx films was elucidated. These amorphous SiOx films were then annealed in N2 atmosphere at 1100℃ for 30 min to be converted into nc-SiOx films. The intensities and the peak positions of the photoluminescence (PL) of these nc-SiOx films were measured to explore how the O/Si ratio of the as-deposited amorphous SiOx films affects the PL signals of the obtained nc-SiOx films after annealing.
The chamber pressure, SiH4/N2O/H2, the plasma power, the pulse-off time (toff), and the substrate temperature were fixed at 0.3 torr, 4/12/80 sccm, 30 W, 50 ms, and 70 ℃, respectively. The ton was varied from 2, 5, 12, 25, 50, 100, 150, 200, 325, 450, 800, 1200 ms, to continuous wave (cw). The thickness of all SiOx thin films was fixed at 310 nm, and the Si-O bonding modes of the SiOx films were measured by Fourier transform infrared spectrometer (FTIR). Energy dispersive spectrometer (EDS), Raman scattering spectrometer, x-ray diffraction (XRD), and high resolution transmission electron microscope (HRTEM) were used to measure and analyze the O/Si ratio and the crystalline structures and sizes of the nc-SiOx films.
EDS results show that, the O/Si ratio of the SiOx films can be controlled between 0.1 and 0.57 for ton changed from 5 to 800 ms in the condition of N2O/SiH4 = 3. FTIR measurements display that there are three peaks of 850 cm-1 (Si-O bending mode), 1060 cm-1 (Si-O-Si stretching mode), and 2240 cm-1 (H-Si-O stretching mode) in each samples. For the ton = 200 ms sample, which the O/Si ratio is 0.57, the intensities of the 850 cm-1 and 2240 cm-1 peaks are in between those of the other samples, and the intensity of the 1060 cm-1 peak is close to the maximum value of all samples. The background fluorescence intensities of the Raman scattering of the nc-SiOx films obtained after annealing is lager than those of as-deposited amorphous SiOx films about 1 to 2 orders. Especially, the ton = 200 ms sample has the maximum value about 92 times. The results indicate that the increasing of the background fluorescence of Raman scattering is due to light scattering from the nanocrystalline silicon (nc-Si) existed in the nc-SiOx films. XRD results present that there are four distinct crystalline signals at , , , and in the ton = 200 ms sample. The peak positions of the PL signals of all nc-SiOx films are located at about 800 nm. The PL intensity of the nc-SiOx film is increased as the O/Si ratio increases from 0.1 to 0.57. The ton = 200 ms sample exhibiting maximum O/Si ratio (0.57) has the strongest PL intensity. Notely, the small variation of peak positions of all samples implies that there is little change in the size of nc-Si in all samples. The variation of PL intensity is mainly influenced by the fraction of nc-Si in nc-SiOx films. The HRTEM data of ton = 200 ms sample shows that the size of the nc-Si is about 3 nm. The fraction of nc-Si in nc-SiOx film is about 33 %, which is estimated from the area ratio of the nc-Si in nc-SiOx film.
The O/Si ratio of the SiOx thin films can be effectively controlled by modulating ton of the pulse-modulated RF power. The PL intensity of the nc-SiOx thin films increases as the O/Si ratio increases from 0.1 to 0.57. The PL intensity of the nc-SiOx films is mainly affected by the fraction of nc-Si in nc-SiOx films.
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