銻化鎵基第一型砷銻化銦鎵/砷銻化鋁鎵量子井之研究及在中紅外線雷射之應用

Abstract

此論文主要致力於銻化鎵基第一型砷銻化銦鎵/砷銻化鋁鎵量子井之探討，並且找尋出更好的長晶方法來提升其光學特性。我們更進一步地利用此銻化合物材料系統來開發於中紅外線應用的發光元件。我們利用了分子束磊晶的技術來成長砷銻化銦鎵/砷銻化鋁鎵四元量子井系統。透過介面處五族元素的控制，我們成長出高品質的量子井材料。在未優化的量子井界面處，時常存在著非理想的局部侷限能階，進而影響激子的複合機制。透過介面處五族元素的控制，我們獲得了擁有優異光學性質的量子井樣品，並且此樣品極少受到局部侷限能階的影響。我們利用溫度相依及激發強度相依的光激發螢光實驗進行了廣泛的量子井探討。在室溫下，我們觀察到波長在2.2微米的高強度且高效率的激子發光。在低溫下，螢光幾乎保持不變的強度，並且極少受到侷限能階的消光作用。量子井隨溫度改變的發光能量變化類似於塊材行為，此現象進一步說明了量子井與周圍能障之間擁有優異的介面性質。因為此良好的介面性質，我們得到了此量子井系統本質的不均勻性線寬擴展只有極小的5 meV。 針對中紅外線的應用，我們發展出兩種型態的雷射元件。第一是中紅外雙波長雷射；第二是中紅外面射型光子晶體雷射。 在單一波導的雷射結構中，我們在主動層成長了兩種不同成分比例的砷銻化銦鎵/砷銻化鋁鎵量子井，並且利用一載子侷限層將此兩種量子井隔開。利用光學注入的方式，我們成功地在室溫下展現出中紅外線雙波長雷射輸出的特性。雷射波長分別為2.31微米與2.61微米，波長差距達300奈米。我們也觀察到在特定的共振腔長度下，兩波長可同時達到閥值條件並且產生雷射輸出。 最後我們成功實現了可高於室溫操作的光激發面射型光子晶體雷射。在室溫下，雷射發光波長在2.3微米，波長半高寬約0.3奈米；雷射的閥值密度約為0.3 kW/cm2。元件表面的正方晶格光子晶體結構提供了光學回饋以及光學耦合機制以達到面出光雷射輸出。此元件可達到在350 K的高溫下操作，隨溫度變化的雷射波長改變速率僅約0.21 nm/K。同時，我們也進行了不同光子晶體蝕刻深度的探討與模擬研究。光場與光子晶體的耦合強度隨著蝕刻深度加深而增加，進而使得雷射波長藍移以及降低雷射閥值，理論模擬與實驗結果可以得到良好的吻合。

In this dissertation we studied the growth and material properties of GaSb-based type-I InGaAsSb/AlGaAsSb quantum wells (QWs) and their applications to mid-infrared (mid-IR) opto-devices. We developed a molecular beam epitaxy (MBE) growth technique that could greatly improve the optical qualities of the QWs. By controlling the group-V elements at interfaces during growth, we were able to achieve high quality QWs free from undesired localized trap states, which might otherwise severely affect the exciton recombination. Strong and highly efficient exciton emissions up to room temperature (RT) with a wavelength of 2.2 m were observed. A comprehensive investigation on the QW quality was carried out using temperature dependent and power dependent photoluminescence (PL) measurements. The PL emission intensity remained nearly constant at low temperatures and was free from the PL quenching from the defect induced localized states. The temperature dependent emission energy had a bulk-like behavior, indicating high quality well/barrier interfaces. Because of the uniformity of the QWs and smooth interfaces, the low temperature limit of inhomogeneous line width broadening was as small as 5 meV. Based on the high quality QWs obtained by the above mentioned technique, we developed two types of mid-IR laser devices in this Sb-based material system. One is a dual wavelength laser and the other is a photonic crystal surface emitting laser (PCSEL). For the dual wavelength lasers, two kinds of InGaAsSb/AlGaAsSb QWs with different compositions were grown as the active region in a single waveguide laser structure. A proper barrier was added in the structure to isolate the two well sections. Two wavelength emissions at 2.31 m and 2.61 m were obtained at RT by optical pumping (the wavelength difference is up to 300 nm). When the cavity length is properly chosen, both wavelengths reach the threshold simultaneously. Second, we demonstrated above RT optically pumped GaSb-based mid-IR PCSELs. The lasers emitted at a wavelength of ~ 2.3 m with a line width of 0.3 nm and a threshold power density of ~ 0.3 kW/cm2 at RT. The square lattice photonic crystal (PC) on the surface provides the optical feedback for laser operation and light coupling for surface emission. The PCSELs were operated with temperatures up to 350 K, showing a small wavelength shift rate of 0.21 nm/K. The PCSELs with different PC etching depth were studied and simulated. As optical field couples more into the PC region due to the increase of etching depth, both the lasing wavelength and the threshold power density decrease. The calculations could fit well with the experimental results.