量子點與量子井結構光學增益及損耗之量測與分析

Abstract

光增益頻譜的量測在瞭解半導體光電元件扮演重要的角色，無論是量子點與量子井的結構，在傳統上，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，我們將介紹一種利用電流激發多段長度（variable-stripe-length method with current injection）的方法，並且以多段元件(multi-section device)的方式來做量測上的改進，量測元件不同激發長度的放大自發性放射光，比較後求得光增益頻譜在量子點與量子井結構上的情形。 論文中，我們討論量子點的樣品和量子井的樣品以探討光增益頻譜在基態和受激態的分佈情形，可以同時觀察到模態增益在受激態與基態的位置。這是使用Hakki-Paoli方法不易觀察到的現象。再者，我們用繼續利用多段元件的方式量測量子點與量子井結構的模態吸收(modal absorption)並且從其中獲得元件的內部損耗（αi）。 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，這將會造成雷射的雷射發光波長由基態轉變至激發態。而由模態吸收量測所求得的內部損耗，則與傳統上利用不同長度雷射共振腔的量測結果相當一致，證實了此量測方法的可靠性。

Gain spectrum measurement plays an important role in analysis of semiconductor 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 variable-stripe-length method with current injection and a multi-section device method to demonstrate the gain spectrum measurement of quantum-dot and quantum-well structures.

In this thesis, we discuss the modal gain in ground states and excited states of quantum-dot and quantum-well samples. We can observe the modal gain in ground and excited states at the same time, which is hardly observed by using Hakki-Paoli method due to the limited wavelength range. Furthermore, we measure the modal absorption of quantum-dot and quantum-well structures by multi-section devices and the internal loss (αi) can be extracted from modal absorption spectrum.

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. The internal loss obtained from modal absorption is the quite same as that from traditional method used by different cavity lengths. These results demonstrate the reliability of the multi-section method.