奈米矽基金氧半記憶體元件與發光二極體

Si Nanocrystal Based Metal-Oxide Semiconductor Memory Devices and Light Emitting Diodes

連佑中(Yu-Chung Lien)

指導教授 ： 林恭如

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2009年)

https://doi.org/10.6342/NTU.2009.10595

摘要

在本論文中，我們主要是利用電漿輔助化學氣相沉積技術法，藉由改變電漿的射頻功率等製程參數，調控富矽氧化矽薄膜層中之奈米矽晶顆粒大小，研究奈米矽晶尺寸與電荷儲存及發光效應的影響。
　　由變溫光激發光的圖譜，我們可以由峰值強度對溫度的關係圖的低溫區斜率萃取出自我補獲激子的能量，此激子為奈米矽晶所特有的現象，我們發現了自我捕獲激子能量與尺寸相依的介電係數呈倒數平方反比的關係。此外，我們亦推導出公式，證明了平能帶電壓位移與奈米矽體積呈正比。最後，電荷儲存在奈米矽晶的保留時間與奈米矽晶的體積呈反比，較大顆的奈米矽晶具有較好的儲存效應。
　　除了奈米矽晶尺寸對電荷儲存之影響，介面奈米錐有助於減少起使電壓，並且增加電致發光的功率；藉由延長每個梯度的停留秒數，我們觀察到奈米矽晶電流阻隔的現象，意謂儲存在奈米矽晶的電荷形成屏蔽電場，抑制其他電荷的儲存。由改變電容電壓磁滯曲線的電壓掃描範圍，我們觀察到奈米矽晶對於電子或電洞的儲存能力具有非對稱的現象。奈米矽晶對電洞具有較好的儲存現象也可以由電容保持時間得到驗證。
　　另外，我們藉由調變電漿輔助化學氣相沉積系統的射頻功率沉積不同組成氧矽比例的薄膜，經過高溫熱退火後集結成不同尺寸的奈米矽，由於量子侷限效應而形成多色彩奈米矽基發光二極體。由光激發光我們可以知道隨著射頻功率的提升，每奈米單位厚度的光激發光強度增加，譜型藍移的現象，可以知道鑲嵌在富矽氧化層中的奈米矽尺寸縮小，但是濃度提升。藉由傅立葉轉換吸收譜型，我們可以由非對稱的矽氧矽拉伸模態估計出退火前的氧矽比例，氧矽比低的薄膜在高溫退火的情形下，晶核成長/熟化現象為主要的機制，在較高的氧矽比的情況下，成核為主要的機制。此外，我們在射頻40及50瓦參數下成長的富矽奈米矽薄膜的光激發光頻譜與藉由矽離子佈值方式形成的富矽奈米矽薄膜的光激發光頻譜類似，它的發光機制由弱氧鍵結缺陷，中性氧空缺所貢獻。由傅立葉轉換吸收譜我們也可以觀察到這些缺陷在經過長時間退火後減少的現象。藉由F-N圖，我們可以知道載子在氧化層中的運輸是由F-N穿隧機制，計算出其位障高度由1.02增加到3.62 電子伏特。在長時間火退火之後，量測到最大的光輸出功率約為0.5毫微瓦。40及50瓦參數成長的元件其P-I斜率，能量轉換效率，內外部量子效率在經過長時間退火後都有劣化的現象，可能與長時間退火後發光缺陷的減少有關。最後，我們觀察到電激發光的頻譜與光激發光的頻譜及拍出來的照片波長相近。

關鍵字

奈米矽晶 ； 富矽氧化矽 ； 導通電壓 ； 電荷儲存效應 ； 保持時間

並列摘要

Temperature-dependent μ-PL of self-trapped exciton (STE) based radiation in Si nanocrystals (Si-ncs) with size enlarging from 2.3 to 4.5 nm is demonstrated, while the monotonically decreasing trend of the STE activation energy (from 1.75 to 1.2 meV) with Si-nc size dependent dielectric permittivity is elucidated by Bohr hydrogen-like atom model. Charge accumulation induced capacitance hysteresis accompanied with lengthened retention is observed when Si-nc size exceeds 2.3 nm. A modified flat-band voltage shift model corroborates the proportionality of the charge density with third power of Si-nc size, supporting that the Si-nc volume is more pronounced than Si-nc density for charge retention. The current blocking and charge accumulation effects of an ITO/Si-rich SiOx/p-Si MOS diode with buried Si nano-dots (Si-nds) and SiOx/Si interfacial Si nano-pyramids (Si-nps) are characterized. At the SiOx/p-Si interface, the area density of Si-nps is increasing from 1.3×109 to 1.6×1011 cm-2, which greatly decreases turn-on voltage of the MOS diode from 182 to 52 V, thus enhancing the electro-luminescent power from 17.5 to 50.4 nW. The current blocking phenomenon of such a MOS diode become serious with lengthening step-voltage delay, indicating that a significant charge accumulation associated with a strong screening field is generated within Si-rich SiOx layer. It was observed that the turn-on voltage with Si-nps evidently decreases to 31.6 V under reverse biased conditions for tunneling holes. Counter-clockwise C-V hysteresis analysis reveals a flat-band voltage shift of 8.5 V for electron and -12.9 V for hole, showing nonlinear function with either Si-nd size or Si-nd density. The C–t retention shows higher charge loss rate for electrons (7.6%) than for holes (1.5%) within 0.5 hr due to low SiOx/Si-nd barrier. The multicolor photo-emission of an ITO/Si-rich SiOx/p-Si MOS diode with buried Si-ncs were demonstrated. From PL analysis, the normalized PL intensity monotonically increases and the peak wavelength blue shifts, indicating the increment of Si-nc density and shrinkage of Si-nc size, respectively. This is attributed to cluster growth/ripening at lower composition ratio and nucleation at higher composition ratio by FTIR absorption analysis of Si-O-Si stretching mode. The PL spectra of 40 and 50 W grown sample also shows similar PL spectrum to Si implanted SiO2 (SiO2:Si+), which are mainly contributed by weak oxygen bonding defect, NOV defect. The FTIR also implies the reduction of radiative defect after long-term annealing. With F-N plot, the turn-on electric field from 2.6 to 9.2 MV/cm, and extract the barrier height from 1.02 to 3.62 eV were determined. The band diagram shows the energy band intrinsically bending more serious for larger Si-nc, indicating smaller external electric field to trigger F-N tunneling mechanism. The maximum optical power of 557.2 nW were observed during long-term annealing device. The EL spectra show similar spectra as PL, and the color of EL patterns are in agreement with their EL spectra.

並列關鍵字

Si-ncs ； silicon rich silicon oxide ； turn-on voltage ； charge storage effect ； retention time

參考文獻

Chapter 1

[1.1] J. Takahashi, T. Tsuchizawa, T. Watanabe, and S. Itabashi, “Oxidationinduced improvement in the sidewall morphology and cross-sectional profile of silicon wire waveguides,” J. Vac. Sci. Technol. B, Microelectron. Process. Phenom., vol. 22, pp. 2522–2525 (2004).

[1.2] T. Tsuchizawa, K. Yamada, H. Fukuda, T. Watanabe, J. Takahashi, M. Takahashi, T. Shoji, E. Tamechika, S. Itabashi, and H. Morita, “Microphotonic devices based on silicon microfabrication technology,” IEEE J. Sel. Topics Quantum Electron., vol. 11, pp. 232–240 (2005).

[1.3] S. McNab, N. Moll, and Y. Vlasov, “Ultra-low loss photonic integrated circuit with membrane-type photonic crystal waveguides,” Opt. Express, vol. 11, pp. 2927–2939 (2003).

[1.4] V. R. Almeida, R. R. Panepucci, and M. Lipson, “Nano-taper for compact mode conversion,” Opt. Lett., vol. 28, pp. 1302–1304 (2003).