鍺量子點在金氧半結構中的分佈對光學特性之影響

Study of the Optical Spectra Affected by the Distribution of the Ge Dots within the MOS Structure

許乃允(Nai-Yun Hsu)

指導教授 ： 管傑雄

國立臺灣大學/電機資訊學院/電子工程學研究所/碩士(2008年)

https://doi.org/10.6342/NTU.2008.10163

摘要

本論文在探索鍺在金氧半元件中的發光特性，主要分成兩個部分。第一個部分為利用高溫爐管退火的方法，將電子束蒸鍍的鍺在金氧半結構中製成多層鍺奈米粒子的元件。第二部分是在矽的表面運用Ebeam製程製作奈米光柵結構，再將鍺量子點長上，形成有光柵結構的鍺量子點MOS元件。並在實驗中觀察其電激發光特性與且運用拉曼頻譜分析鍺結晶情形與介面的特性。
在多層鍺量子點元件的拉曼譜線中可以發現，當元件在高溫退火時，鍺會開始從非晶系(amorphous)慢慢結晶化(crystalization)，直到退火溫度為900℃時其拉曼頻譜的半高寬達到最小，晶格缺陷密度最低，進一步量測退火900℃的鍺量子點元件之電激發光，但只有觀察到矽的發光，沒有量測到鍺的發光。為了分析鍺與氧化層介面的特性，我們將穿隧氧化層去掉，製作氧化層-鍺-矽元件，讓足夠的載子到達鍺量子點，發現其電激發光光譜在波長較大的地方有缺陷所放出的光，顯示氧化層與鍺的介面存在許多缺陷，使得鍺無法有效放光。
第二部分探討奈米光柵對鍺量子點MOS 元件光學特性之影響。元件之製作係利用電子束微影技術設計並曝光出奈米線寬之光柵，利用ICP-RIE 乾蝕刻技術蝕刻出光柵結構。首先將製作出之樣品光柵量測矽的增強拉曼散射訊號，接著量測鍺的拉曼譜線。實驗中，我們改變的參數為光柵之週期，實驗得知此週期越小，矽的拉曼譜線的增強效果就越強，在週期400 奈米的拉曼增強效果可達到七倍，另外在TM 模態的增強效應也比TE 模態大。接著量測在光柵上成長鍺量子點的拉曼譜線，發現在週期為800 奈米的拉曼增強效應最大，增強倍率約為兩
倍，雖然在製作成元件後沒有量測到鍺的發光訊號，但由光柵來增強拉曼訊號，對未來矽鍺元件光學特性的研究提供更多發展空間。
本實驗深入的探討鍺量子點在氧化層中成長過程的拉曼頻譜特性，並分析出鍺量子點難以在氧化層中發光的原因。第二部分運用光柵結構增強拉曼散射是一個前驅性的研究，其物理機制雖然尚待研究，但是如此不錯的成果給了我們繼續研究的力量，也希望能夠結合半導體製程製作出方便且精確性高之整合性光學量測元件，並能做更多的應用。

關鍵字

鍺量子點 ； 矽鍺元件 ； 電激發光 ； 電子束微影 ； 拉曼光譜

並列摘要

In the thesis the optical spectra affected by the distribution of the Ge dots within the MOS structure are reported. There are mainly two series of experiments in this thesis. First, the multi-layer Ge dots within the MOS structure are manufactured by E-gun evaporation and high temperature annealing. Second, grating on the Si bulk are manufactured by E-beam lithography and Ge dots are formed on the grating. To analyze the device characteristics, electro-luminescence (EL) measurement and Raman system are used in these experiments.
By analyzing the Raman spectra, the multi-layer amorphous Ge films begin to crystallize at high annealing temperature, and when the annealing temperature reaches 900℃, the full width at half maximum (FWHM) is the minimum, it means the defect density of the device is small. The EL spectra of the device, annealed 900℃, only show the light from Si. In order to find the reasons that the Ge film did not emit light, the devices with Oxide-Ge-Si structure are fabricated. These Oxide-Ge-Si devices emit light at longer wavelength and we believe that the light is emitted by the defects at the interface between Ge and Oxide.
To improve the optical characteristics, the grating structure is introduced to the Ge dots MOS structure. The grating enhances the intensity of Si and Ge Raman spectra. Although the light emitted from Ge is not found in the thesis, the advantages of grating we stated in the thesis are helpful in the research of Ge and Si optical properties in the future.
In the second section, the effect of the grating on the Si bulk and Ge dots is investigated. Grating on the Si bulk are manufactured by E-beam lithography and ICP-RIE. While the pitch becomes smaller, the intensity of the Si Raman spectrum becomes larger. The intensity is enhanced 7 times while the pitch is 400 nm. The enhancement effect of TM mode is better than TE mode. Furthermore, the Raman of the Ge dots on the Si grating is discussed. The enhancement is the largest when the pitch is 800 nm.
The Raman spectra of the Ge dots in the MOS structure are investigated. Although the light emitted from Ge is not found in the thesis, the mechanism which causes the lack of the light from Ge is found. In the second section, the enhancement of the Raman scattering with grating is a forerunner research. Consequently there are lots of researches are going to be done. In the future, we hope to understand the mechanism, and to integrate the semiconductor processes to fabricate the integrated optical detection devices.

並列關鍵字

Ge quantum dots ； Si/Ge device ； Electro-luminescence ； Ebeam lithography ； Raman spectroscopy

參考文獻

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