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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/8881


    Title: 砷化銦量子點異質結構與雷射;InAs/GaAs quantum dot heterostructures and lasers
    Authors: 葉念慈;Nien-Tze Yeh
    Contributors: 電機工程研究所
    Keywords: 分子束磊晶;量子點;半導體雷射;molecular beam epitaxy;quantum dots;semiconductor laser
    Date: 2001-07-10
    Issue Date: 2009-09-22 11:36:58 (UTC+8)
    Publisher: 國立中央大學圖書館
    Abstract: 本論文主題是成長及製作砷化銦(鎵)量子點異質結構與雷射,並且探討量子點元件的特性。 我們首先在砷化銦鎵量子點中加入 p 型(鈹)及 n 型(矽)的摻雜物,觀察其做為量子點雷射活性層時,對雷射特性產生的影響。雷射波長、特徵溫度、量子效率及內部損耗都與摻雜物有關,並與由原子力顯微鏡所顯示的量子點大小與均勻性有關。其中鈹摻雜的量子點雷射可達到室溫連續波操作的優異特性,而未摻雜的量子點雷射則在室溫附近有較高特徵溫度達125 K。 我們也發現多層堆疊的量子點雷射特性會被量子點間的砷化鎵間隔層厚度所影響,如果將間隔層厚度由30奈米降到10奈米可具有光激光譜的線寬降低、雷射臨界降低、提高特徵溫度及內部量子效率等優良特性。這種現象可歸因於間隔層厚度引發量子點均勻性的不同而導致非均相性的寬化。 為了能使量子點雷射應用於光纖通訊,延伸發光波長至可使用的範圍,我們接著利用光激光系統,研究對自我組成砷化銦量子點異質結構使用不同環境材料相依的應力效應。其中一系列的試片是研究量子點在相對於所謂的應力緩衝層位置不同所引發的應力效應。因應力緩衝層可減低殘餘的靜應力,將砷化銦量子點置於砷化銦鎵應力緩衝層下方時可得到 1.34 微米的長波長。我們觀察到波長與位於量子點上方的應力緩衝層的厚度有關,顯示環境材料在量子點應變鬆弛的過程中扮演重要的角色。由另一組實驗中,我們使用砷化銦鋁取代砷化銦鎵作為應力緩衝層時也進一步證明此論點。因砷化銦鋁的彈性係數較砷化銦鎵大,使得在砷化銦鋁應力緩衝層下方的量子點中,較少的應力能被移除,波長產生藍位移。 製作成量子點發光二極體後,我們也觀察砷化銦量子點與砷化銦鎵應力緩衝層排列的順序對光特性所產生的影響。當砷化銦量子點上方覆蓋砷化銦鎵量子點時,光激光波長可超過 1.3 微米。相同的試片中,低電流時的基態發光半高寬僅 19 毫電子伏特,基態飽和時不超過 40 毫電子伏特。我們也發現此量子點發光二極體的量子效率及飽和強度較其他試片為高,可歸因於在量子點上方加入應力緩衝層後使量子點密度增加所致。 最後我們使用固態分子束磊晶器,以砷化銦/砷化鎵量子點作為活性層,磷化銦鎵作為被覆層製作半導體雷射並量測其特性。這些不含鋁成分的量子點雷射在室溫下具有起振電流密度 138 A/cm2 ,內部損耗 1.35 cm-1 和內部量子效率達 31 %。在低溫時,特徵溫度可達425 K而起振電流僅30 A/cm2。 This thesis covers the growth and characterization of In(Ga)As quantum dot (QD) heterostructures and lasers. QD lasers with different doping schemes in the In0.5Ga0.5As QD active region are investigated. Their lasing wavelength, characteristic temperature, quantum efficiency, and internal loss are characterized and correlated with the size, uniformity, and density of the QDs revealed by atomic force microscopy. Room temperature continuous-wave operation of Be-doped quantum-dot lasers has been achieved. Undoped In0.5Ga0.5As quantum-dot lasers with a characteristic temperature as high as 125 K above room temperature have also been demonstrated. It is also found that the performance of In0.5Ga0.5As/GaAs multi-stack QD lasers is sensitive to the GaAs spacer thickness between the dots. Reducing the spacer thickness from 30 nm to 10 nm leads to narrow photoluminescence linewidth, low threshold current, high characteristic temperature and high internal quantum efficiency. This behavior is attributed to inhomogeneous broadening caused by dot size fluctuation related to spacer thickness. We then study the matrix-dependent strain effect in self-assembled InAs QD heterostructures using photoluminescence measurements. A series of samples is prepared to examine the effect of QD position with respect to the so-called strain-reducing layer (SRL). Since the SRL reduces the residual hydrostatic strain in the QDs, long emission wavelength of 1.34 mm is observed for the InAs QDs with an In0.16Ga0.84As SRL. The dependence of the emission wavelength on the thickness of the cap layer on SRL also indicates the critical role of the matrix that plays in the strain relaxation process of the dots. This is further confirmed by using In0.16Al0.84As instead of In0.16Ga0.84As as the SRL. A blue shift in wavelength is observed because the elastic stiffness of In0.16Al0.84As is higher than that of In0.16Ga0.84As and less strain is removed from the dots with In0.16Al0.84As SRL. The effects of the arrangement between InAs QDs and InGaAs SRL on the optical properties of QD light emitting diodes are also investigated. Electroluminescence wavelength longer than 1.3 mm is obtained as InAs QDs are covered with a thin InGaAs SRL. For the same sample, the full width at half maximum of the ground state emission peak is as narrow as 19 meV at low injection current, and less than 40 meV even at saturation condition. It is also found that the slope efficiency of the diode is higher than that of other samples in the linear region and its light output saturation level is higher because of its higher density of QD. Finally, we present the lasing properties of InAs/GaAs QD lasers with InGaP cladding layers grown by solid-source molecular beam epitaxy. These Al-free lasers exhibit a threshold current density of 138 A/cm2, an internal loss of 1.35 cm-1 and an internal quantum efficiency of 31 % at room temperature. At low temperature, a very high characteristic temperature of 425 K and very low threshold current density of 30 A/cm2 are measured.
    Appears in Collections:[電機工程研究所] 博碩士論文

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