矽奈米晶體金氧半元件光電性質之研究

本論文主要研究矽和奈米晶體金氧半元件在偏壓下的光激發螢光(photoluminescence, PL)的變化和奈米晶體的光學增益(optical gain)的現象。本論文可以主要分成三部分。第一個主題是研究矽金氧半元件在偏壓下PL強度變化的情形。當閘級偏壓加在金氧半元件上時，它的PL強度會隨著矽晶體內的電場而有顯著的變化，而這變化乃是輻射複合(radiative recombination)和非輻射複合(nonradiaive recombination)機制相互競爭的結果。我們建立一個簡單的理論模型來解釋此現象，發現PL強度最低點發生在非輻射複合速率最大值之處。藉由輻射複合和非輻射複合機制的相互競爭，在偏壓下的PL強度會隨著矽和氧化矽表面缺陷以及氧化矽內部電荷的正負與大小，而有所改變及偏移。第二個主題是探討矽奈米晶體金氧半元件的電性與在偏壓下PL強度的變化。我們從在室溫時的電容-電壓以及電壓-電流曲線觀察到電子被填充在矽奈米晶體內，平均一顆矽奈米晶體約儲存約五十顆電子。而且我們運用前一主題所述PL強度隨著偏壓而變化的曲線來檢測氧化層中所儲存的電荷，發現在偏壓下PL強度變化的曲線往右偏移，顯示負電荷的存在。我們可以藉由電子缺陷存在於矽奈米晶體中來解釋電容-電壓曲線和在偏壓下PL強度曲線所發生的變化。第三個主題是矽奈米晶體其光學增益現象的觀察報告。我們在室溫下藉由高功率雷射的激發觀察到矽奈米晶體的自發輻射放大(amplified spontaneous emission, ASE)的現象，在實驗上證實在矽奈米晶體中居量反轉(population inversion)的發生。藉由矽奈米晶體的載子侷限(carrier confinement)效應和使用摻雜鋁之氧化鋅(aluminum-doped zinc oxide, AZO)薄膜作為抗反射層(anti-reflection coating)，矽奈米晶體展現出更高的光學增益值。我們觀察到這些光學增益值會隨著溫度與偏壓的不同而發生改變來排除ASE現象來自於人為疏失或實驗架構上的假訊號所造成。

關鍵字

原子層沉積技術；矽奈米晶體；光激發螢光；電壓電容法；光學增益

並列摘要

This thesis presents the study of bias-dependent photoluminescence (bias-PL) of Si bulk and nanocrystals in metal-oxide-semiconductor (MOS) structures and the optical gain of Si nanocrystals. This thesis is divided into three main topics. The first is bias-dependent photoluminescence from the Si MOS structure at room temperature. Significant variation of PL intensity as a function of electrical field across the Si bulk was observed by applying an gate voltage on the MOS structure. The competition between radiation and non-radiation recombination results in the change of PL intensity. The bias-PL characteristics can be fitted pretty well by the theoretical model, and the minimum of bias-PL curve results from the maximum Shockley-Read-Hall nonradiative recombination rate. The bias-PL curve is significantly affected by the interface trap density and the effective oxide charge. This phenomenon can be used to probe the interface quality between the oxide and the semiconductor. The second topic is the electrical and bias-PL characteristics of Si nanocrystals in the MOS structure. The charge storage in the Si nanocrystals in the MOS structure was observed from the capacitance-voltage (CV), current-voltage, and bias-PL curves. The number of electrons stored in the Si nanocrystals is around 50 per nanocrystal. The bias-PL method can be used to examine the charge stored in Si nanocrystals, and it is consistent with the result obtained from CV method. Furthermore, the electron traps exist in the Si nanocrystals was used to account for the observed hysteresis in the CV curves and the shift in the bias-PL characteristics. The third topic is the observation of optical gain in Si nanocrystals using the variable stripe length (VSL) method. The amplified spontaneous emission (ASE) was observed under a high-power laser excitation at room temperature, and so the experimental evidence of population inversion in Si nanocrystals was achieved. Because of the carrier confinement effect in Si nanocrystals and the anti-reflection coating by the aluminum-doped zinc oxide layer, Si nanocrystals exhibit positive optical gain under a high-power laser excitation. The dependence of optical gain on the temperature and applied gate voltage were also observed, indicating that the ASE signal can be excluded from the artificial effect and experimental flaws in the VSL configuration.

並列關鍵字

Atomic layer deposition ； Si nanocrystals ； Bias-photoluminescence ； Capacitance-Voltage ； Optical gain

參考文獻

[27] Cambridge Nanotech Inc. “An Overview of Atomic Layer Deposition: Principles and Applications of ALD”

Chapter 1

[1] P. Woditsch and W. Koch, “Solar grade silicon feedstock supply for PV industry,” Solar Energy Materials and Solar Cells, 72, 11-26 (2002)

[3] E. Cortesi, F. Namavar and R. A. Soref, “Novel silicon-oninsulator structures for silicon waveguides,” IEEE SOS/SOI 89 (1989)

[4] R. A. Soref, E. Cortesi, F. Namavar and L. Friedman, “Vertically integrated silicon-on-insulator waveguides,” IEEE Photonic Tech. Lett.

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矽奈米晶體金氧半元件光電性質之研究

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