以電激發長度變化法量測量子點結構之光學增益

Optical Gain Measurement of Quantum-dot Structures by Using a Variable-stripe-length Method with Current Injection

高健凱(Chien-Kai Kao)

指導教授 ： 毛明華

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2004年)

https://doi.org/10.6342/NTU.2004.02338

摘要

光增益頻譜的量測在瞭解量子點光電元件扮演重要的角色，傳統一般使用Hakki-Paoli方法，藉由量測雷射的Fabry–Perot模態在低於臨界電流下，藉以換算求得光增益頻譜。在論文中，我們將介紹一種新的方法利用電流激發多段長度（variable-stripe-length method with current injection）比較後求得光增益頻譜在量子點結構。
論文中，我們討論具不同量子點層數的樣品C1511(10層量子點)，C1512(5層量子點)，C1513 (3層量子點) 和 SH239(15層量子點)藉以探討光增益頻譜在基態和受激態的分佈情形。我們再觀察最大光增益在受激態超越基態。這是使用Hakki-Paoli方法不易觀察到的現象。再者，我們用一種新的方式量測量子點結構的內部損耗（αi），以C1511，C1512，C1513討論其內部損耗。
根據我們的量測與分析的結果，說明了激發態增益對整個增益頻譜的影響，尤其是在較高的電流激發下。這將會造成量子點雷射的雷射發光波長由基態轉變至激發態。

關鍵字

量子點 ； 光學增益 ； 多段電激發 ； 內部損耗

並列摘要

Gain spectrum measurement plays an important role in analysis of quantum-dot electro-optic devices. Traditionally, the Hakki-Paoli method is used to measure the modulation depth of the Fabry–Perot mode spectrum of lasers below threshold. In this study, we introduce a new variable-stripe-length method with current injection to demonstrate the gain spectrum measurement of quantum-dot structures.

In this thesis, we measure four samples with different numbers of quantum-dot layers, C1511 (10 layers of quantum dots), C1512 (5 layers), C1513 (3 layers), and SH239 (15 layers), to discuss their modal gain in ground states and excited states. We observe the gain peak of the excited states surpasses that of the ground states, which is hardly observed by using Hakki-Paoli method due to the limited wavelength range. Furthermore, the transmission experiment is applied to measure internal loss (ξ). From our results, ξ of C1511, C1512 and C1513 are 1 cm-1, 1.35 cm-1, and 3.2 cm-1 respectively. We find that the optical mode loss does not increase as the layer number increases.

Based on the results in our measurement and analysis, the contribution of excited states to the gain spectra, especially under higher excitation, will be demonstrated. This will cause lasing emission wavelength to shift from ground states to excited states in QD lasers.

並列關鍵字

Internal loss ； Quantum-dot Structures ； Modal gain ； Variable-stripe-length Method

參考文獻

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