以氣態源分子束磊晶法成長三五族化合物半導體量子結構與元件

Growth of III-V Compound Semiconductor Quantum Structures and Devices by Gas-Source Molecular Beam Epitaxy

林佑儒(You-Ru Lin)

指導教授 ： 林浩雄

國立臺灣大學/電機資訊學院/光電工程學研究所/博士(2009年)

https://doi.org/10.6342/NTU.2009.10198

摘要

在本篇論文中，分為兩個研究主題: 1.銻砷化鎵/砷化鎵第二型量子井結合鄰近砷化銦量子點應力子的量子結構與雷射元件成長 2.砷化鎵成長於奈米矽溝渠。上述二者均使用氣態源分子束磊晶法成長。首先，我們研究銻砷化鎵/砷化鎵第二型量子井結合砷化銦量子點應力子的複合結構。5-nm 厚度間隔層的複合結構相較於純粹第二型銻砷化鎵單量子井，在低溫低激發強度的螢光頻譜上出現44 meV的紅移，且變溫螢光頻譜顯示較佳的放光強度和更寬的半高寬。紅移現象說明由鄰近的量子點產生的應力在第二型量子井界面上誘發了區域性的位能低點。隨著溫度增加，原本侷限在量子點內的載子部分獲得熱能離開量子點，留下帶電荷的量子點，因此產生的電場增加第二型量子井界面上位能的波動且增加載子在界面上復合放光的機率。我們使用相同複合結構當做雷射主動層，發現以5-nm 厚度間隔層的複合結構，可降低原本銻砷化鎵第二型單量子井的起振電流密度、內部光學損耗，並增加內部量子效率、模態增益和特徵溫度，原因在於砷化銦應力子在量子井界面上增強了位能波動，使得躍遷矩陣元素增加。第二部分，我們使用氣態源分子束磊晶法成長並研究砷化鎵於有圖案的矽奈米溝渠，樣品是由台灣積體電路股份有限公司(TSMC)所提供。為了避免分子束遮蔽效應發生在奈米矽溝渠的成長過程中，將主要分子束對準奈米矽溝渠的長邊而成功解決此問題；我們也研究了砷化鎵於二氧化矽與矽溝渠的選擇性磊晶條件，基板溫度在580℃以上就不會有砷化鎵遺留在二氧化矽表面。穿透式電子顯微鏡截面影像顯示當寬度降至85 nm以下時，已不會有穿透差排(threading dislocation)出現，但仍有微雙晶面(micro-twins)的產生。我們對於溝渠內的砷化鎵進行了拉曼光譜與陰極放光的研究︰發現砷化鎵成長於矽溝渠內產生TO聲子模態訊號，我們認為代表拉曼選擇規則不被遵守是因為三種可能︰晶體內有微雙晶面、多面向的表面和尺寸縮小效應。我們也觀察到另三種拉曼散射能量，SO聲子模態、As-As鍵結能量和Si-2TA；成長於溝渠內的GaAs的CL訊號較於GaAs塊材訊號，寬的線寬和峰值位置偏移，原因來自於交互摻雜(cross-doping)，由於晶格不匹配產生的應變，還有從表面與界面空乏區產生的斯塔克效應(Stark effect)影響；另外也可在可見光波段發現SiO2產生的放光。據我們所知，這是首次使用分子束磊晶法成長砷化鎵磊晶於奈米矽溝渠寬度小於100 nm的研究。

關鍵字

砷化銦/砷化鎵量子點 ； 銻砷化鎵/砷化鎵量子井 ； 奈米矽溝渠

並列摘要

The dissertation contains subjects: namely, GaAsSb/GaAs type-II quantum well (QW) with an adjacent InAs quantum-dot (QD) stressor layer and GaAs grown on Si nano-trench. The growths in both subjects are carried out by gas-source molecular-beam epitaxy (GSMBE).
First, we study the structural and optical properties of a composite structure consisting of GaAsSb type-II QW well with an adjacent InAs QD stressor layer. From 19-K photoluminescence (PL) spectra, we observed a 44-meV red-shift in emission energy in the composite structure with 5-nm thick spacer layer in between the QW and QD as compared with a type-II GaAsSb/GaAs single QW structure, which indicates that the strain induced by the adjacent QDs produces local potential minimums in the interface of the type-II QW. From the temperature-dependent PL results, the sample with composite structure shows stronger intensity and broader line-width than the GaAsSb/GaAs single QW structure. With increasing temperature, a part of carriers localized in the QDs are thermalized. Their escape leaves the QDs charged, which modulates the electric field between the QDs and the QW and enhances the potential fluctuation in the interface of QW. As a result, the probability of carrier recombination increases due to the additional confinement provided by the modified potential fluctuation. We use the composite structure as the active region of edge-emission laser diodes. Lasers with composite structure show lower threshold current density and internal optical loss than the GaAsSb/GaAs QW lasers. Better internal quantum efficiency, modal gain and characteristic temperature are also demonstrated. We ascribe these advantages in laser characteristics to the larger optical transition element in the composition structure, resulting from the additional potential fluctuation provided by the charged QDs.
In the second part of this work, we studied the growth of GaAs in patterned Si nano-trenches provided by TSMC. In order to avoid the shadowing effect, the major molecular beams were aligned with the longitudinal direction of the nano-trenches. We found that when the growth temperature is higher than 580C, no GaAs is left on the surface of SiO2, and the selective epitaxial growth of GaAs in Si trenches is achieved successfully. Cross-sectional transmission electron microscopic images show that no threading dislocations but micro-twins exist in the GaAs deposited in the Si nano-trenches. Raman spectroscopy and cathodoluminescence (CL) were used to analyze the GaAs grown in the Si nano-trenches. Beside the LO and TO modes of GaAs, we indentified three additional modes, a surface mode in between the TO and LO modes, the Si-2TA mode, and a mode with its peak wave-number smaller than that of the TO mode. Room temperature CL bands from GaAs grown on Si nano-trenches show broaden linewidths and peak energies deviated from that of bulk GaAs, which is attributed to the cross-doping during the growth, strain in the GaAs resulting from lattice mismatch, and Stark shift resulting from the surface and interface depletion regions. In addition, emission bands from SiO2 were also observed. As far as we know, it is the first GaAs epitaxial film grown in Si nano-trench with a width less than 100 nm by GSMBE.

並列關鍵字

InAs/GaAs quantum dot ； GaAsSb/GaAs quantum well ； nano-Si-trench

參考文獻

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