半導體量子點光源增益頻譜之研究

Abstract

本論文討論了經由改良型的「分段式接點法」所量測的砷化銦量子點雷射元件淨光學模態增益以及吸收頻譜。傳統的分段式接點法施加電壓於第一段及第二段進而計算出增益頻譜，然而改良過後的分段式接點法除了第一段和第二段，進一步使用到第三段，透過一些理論上的驗證，經由漏電流產生的非導向性自發性輻射引起的誤差可在運算中被根本性地消除，最後得到精確的增益和吸收頻譜。在本論文中首先會呈現從量子點脊狀式波導雷射二極體的電性和光性等特性以及從中萃取的參數，接著是一系列關於改良型及傳統型分段式接點法的比較，最後是和從雷射二極體萃取出的參數做比較，我們發現，改良型分段式接點法不論是在基態飽和增益、「電流-光模增益」的關係和內部吸收上都有較高的精確度，而從傳統型分段式接點法的增益及吸收頻譜中，可以觀察到非導向性自發性輻射的影響，改良型分段式接點法的精確性在這邊得到了驗證。此外，我們也討論了吸收區接地與否對增益頻譜的影響。最後我們會呈現由計算出的增益頻譜逆推回去算出的半導體量子點結構中未經放大的自發性輻射。藉由改良型分段式接點法，就算材料的增益非常小，我們仍舊可以從中萃取需要的參數。此外，往後參數的萃取可以在一片元件上完成，不像以往要切很多個共振腔長度，提供了一個便利且省時又不失精準度的量測方式。

We discuss an alternative segmented contact method for accurate optical gain and loss spectra calculations of InAs/InGaAs quantum dot (QD) active materials. The error usually comes from unguided spontaneous emission. In order to eliminate it, triple biased sections against double biased section in conventional segmented contact method scheme is applied, and the error is reduced by subtracting background signal resulting clean and accurate gain and loss spectra [1]. In this thesis, we demonstrate the characterizations of QD ridge waveguide laser diodes firstly. Then, a set of detail analysis is applied between conventional and improved segmented contact methods. The devices’ current density versus modal gain curve is measured to a precision of 95.8% compared with that extracted from typical ridge waveguide laser process. The effect caused by absorber shorted to ground or not is discussed. The internal optical mode loss is also described. Finally, we demonstrate the unamplified electro-spontaneous emission spectra from conventional and improved methods. By improved segmented contact method, characterization of a semiconductor laser device could be done on a single sample instead of processing lots of cavity lengths. On the other hand, one can characterize very low gain material samples that are difficult to extract by other techniques.