光與奈米晶矽的非線性交互作用

Nonlinear Optical Interaction in Nanocrystalline Silicon

李荐軒(Chien-Hsuan Li)

指導教授 ： 朱士維

國立臺灣大學/理學院/物理學研究所/碩士(2022年)

https://doi.org/10.6342/NTU202200687

摘要

最近幾十年來，半導體業的發展十分迅速，我們現在已經可以將數以億計的電晶體放在極微小的晶片中，讓各式各樣的電子產品達成我們想要的功能。而電晶體運作的關鍵機制在於輸入與輸出的非線性，達成電控制電的功能，由於矽元素在地球上的含量相當豐富，使矽成為積體電路中不可或缺的材料之一。
此外，矽的高折射率以及相較於金屬有較低的非輻射損失，讓矽在光學上也具有發展的潛力，不過矽塊材的光學非線性因子太過微小，在光訊號的控制上成為一大瓶頸。近年，我們透過光熱效應與米氏共振理論設計奈米晶矽的共振腔，有效將非線性折射率因子n2提升了數個數量級，達到10-1微米平方每毫瓦，可以有效改變奈米晶矽的折射率，產生夠大的光學非線性，讓矽光子學的發展向前邁進一步。但在先前的研究中，我們僅展示非線性散射，由於折射率的實部與虛部分別對應散射與吸收，預期在吸收也會有非線性。
本研究中，我們透過雷射掃描顯微鏡，探討不同共振模態奈米晶矽的非線性散射與非線性吸收，其中散射是指反向散射；而吸收是由材料溫度判斷。我們使用拉曼光譜學量測奈米晶矽的溫度，但為了同時對應非線性散射與吸收，不採取傳統定點量測的方式，而是將掃描過程所得的拉曼位移進行溫度分析。從實驗結果中發現特定大小粒子溫度上升斜率改變四倍，證實吸收也存在非線性。同時也利用理論進行模擬，將奈米晶矽散射與吸收的實驗結果與理論互相連結，另外，我們發現拉曼散射也具有非線性，可能會影響由公式中計算出的粒子溫度。

關鍵字

矽光子學 ； 非線性 ； 光熱效應 ； 奈米晶矽 ； 拉曼光譜學

並列摘要

In recent decades, the development of the semiconductor industry has been rapid. To achieve the desired function, billions of transistors are placed on a tiny chip. The operation principle of a transistor is based on the nonlinearity between input and output. In a transistor-based integrated circuit, silicon is one of the indispensable materials due to its natural abundance. Inspired by the success of silicon electronics, many efforts went into developing silicon photonics devices due to the high refractive index and low non-radiative loss of silicon. However, the nonlinear optical index of bulk silicon is only 10-9 m2/mW. Recently, we have designed the nanocrystalline silicon resonant cavity to boost photothermal nonlinearity to 10-1 m2/mW via Mie resonance.
In our previous research, we focused on nonlinear scattering. However, as the photothermal effect occurs, we also expect the absorption to exhibit nonlinearity since the refractive index's real and imaginary parts correspond to scattering and absorption. Here, we demonstrate the nonlinear absorption of nanocrystalline silicon with different resonance modes through laser scanning microscopy. We use Raman spectroscopy to measure nanoscale temperature, which represents absorption. For the particle with absorption nonlinearity, the temperature rising slope dramatically changes four times as excitation intensity increases. Moreover, an inconsistency between experiment and simulation suggests that conventional Raman thermometry may not be valid for this particle. This result opens a fundamental problem: how to calculate the temperature of nanoparticles under the influence of nonlinear absorption.

並列關鍵字

silicon photonics ； nonlinearity ； photothermal effect ； nanocrystalline silicon ； Raman spectroscopy

參考文獻

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