量子點雷射之增益和特徵溫度研究

The Investigation of Gain and Characteristic Temperature in Quantum Dot Lasers

曾煒傑(Wei-Chieh Tzeng)

指導教授 ： 林清富

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2006年)

https://doi.org/10.6342/NTU.2006.01135

摘要

隨著成長量子點技術的成熟，我們期待瞭解量子點的特性，以使光纖通訊得到充分利用。本論文中，我們利用所設計量子點結構，來開發溫度依賴性更低，臨界電流更小，調變頻寬更寬的半導體雷射與光放大器。

我們利用新型的兩段式波導元件，使用新的測量增益的方法，在不需要外部雷射及複雜的實驗架設之下，對各個電流密度與溫度快速且準確的測量其寬頻增益頻譜。增益頻譜曲線是由均勻性變寬與非均勻性變寬兩個成分所構成。均勻性變寬成分是由載子生命期所決定，而非均勻性變寬成分意指載子數目對其能量的分佈不均勻，主要原因是量子點數目對其尺寸分布不均勻，另外，第一、第二與第三量子化能態的兼併數的比例是二比四比六也決定非均勻性變寬成分在這三個能態的高度。增益頻譜曲線除了因電流密度增加與溫度增加而紅移，還會受到電子佔據機率的影響，其費米能階會因電流密度增加而上升，因溫度增加而下降。

量子點的臨界電流對溫度關係無法用單一特徵溫度描述，特徵溫度會隨溫度改變。我們也在長波長區段發現到特徵溫度的負溫度效應，這是增益曲線紅移所造成的。當溫度上升，帶隙能量會減少得到更長的放射波長。

關鍵字

量子點 ； 光纖通訊 ； 增益頻譜 ； 臨界電流 ； 特徵溫度

並列摘要

With the improvement of quantum dot growth technology, we investigate the characteristics of quantum dot lasers to fully utilize the available bandwidth of optical fiber communication systems. In this dissertation, we focus on the designed quantum dot structures to achieve less temperature dependence, lower threshold current density and higher tuning bandwidth of semiconductor laser diodes and semiconductor optical amplifiers.

We propose a new simple method to measure the broadband gain spectrum with a two-section device. Without any other external tunable lasers and complicated setup, broadband gain spectrum is obtained immediately and precisely for each current density and temperature. Broadband gain spectrum comprises two compositions, one is homogeneous broadening arising from carrier lifetime, the other is inhomogeneous broadening which represents the size uniformity of quantum dots. Besides, the proportion of degeneracy in first, second and third quantized state is 2 to 4 to 6 which decide the amplitude of these states. Broadband gain spectrum red shifts when current density increase and temperature increase, and also influenced by electron occupation probability with its fermi-level increasing with increasing current density and decreasing with increasing temperature.

The temperature dependence of threshold current is not described by a single exponential term with a characteristic temperature. Characteristic temperature of quantum dots varies with temperature. We also find negative temperature effect of characteristic temperature, which arises from red shift of gain curve. when temperature increases, the bandgap energy can be further decreased to achieve a longer emission wavelength.

並列關鍵字

quantum dot ； fiber communication ； gain spectrum ； threshold current ； characteristic temperature

參考文獻

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