在磷化銦基板上的第二型砷化銦鎵/砷銻化鎵量子井中紅外光雷射

Abstract

此論文利用分子束磊晶在磷化銦基板上成長中紅外光半導體雷射。其中，主動層之選擇有別於一般高應力之砷化銦量子井，採用的是第二型砷化銦鎵/砷銻化鎵量子井，藉由量子井等效能隙可調之特性，以延伸發光波長，並且有效減少量子井的應力。內文主要分為三部分：主動層結構設計與比較、(光)電激發雷射特性分析以及雷射散熱探討與改進。第一部分藉由理論計算，適度調整砷化銦鎵/砷銻化鎵量子井之寬度及組成，以達到發光波長與雷射增益之間的平衡。第二部分，我們首度實踐了‘M’型量子井雷射，並利用光激發的方式分析此結構與一般‘W’型量子井雷射之差異。再進一步以‘W’型量子井出發，把原本分隔每個‘W’型量子井的砷化鋁銦改為砷銻化鎵以利於載子傳輸。此砷銻化鎵也同時扮演了應力補償的角色，以維持主動層的晶格品質。再搭配不含銻的砷化鋁銦鎵作為侷限層，實現了極低臨界電流且發光波長達到2.35微米之電激發雷射。然而，從光激發螢光與雷射光電特性分析得知磊晶仍有些不完美的特性，例如:局域態的形成、非線性的功率-電流曲線以及偏低的內部量子效率等。本文也針對這些缺點加以探討。第三部分，我們以連續電流輸入的方式操作雷射，發現雷射因為過熱而無法正常輸出。因此我們利用金錫共晶的接合方式，把單顆雷射以磊晶面向下的方式接合在氮化鋁散熱基板上，改善了散熱問題。最終，我們實現了連續電流輸入的電激發雷射，在室溫下最高輸出功率為0.92毫瓦，大大地提升了此中紅外光半導體雷射實際應用的價值。

In this thesis, the mid-infrared lasers were grown on InP substrates by the molecular beam epitaxy system. Highly strained type-I InAs QW was often used to be the active region to extend lasing wavelength. However, to reduce the stress, the type-II InGaAs/GaAsSb QW was applied and it was proposed for longer emission wavelength because of the tunable effective bandgap. The thesis is composed of three parts : the design and comparison of the active region, the characteristics of the optical pumped and electrical pumped lasers as well as the discussion and improvements of the heat dissipation of the laser devices. First, by varying the thickness and the composition of the InGaAs/GaAsSb QWs respectively, the tradeoff between emission wavelength and material gain is discussed with the theoretical calculations. Second, we demonstrate the first ‘M’-type QW laser. By the optical pumped measurement, the differences between ‘M’-type and ‘W’-type QW lasers are discussed. To realize the electrical pumped laser, the original InAlAs spacing layer is replaced by the GaAsSb layer for better carrier transport. The GaAsSb layer also plays the role of strained compensation in the active region to maintain the crystal quality. Furthermore, by applying the Sb-free InAlGaAs as the separated confined layer (SCL), the low threshold current ‘W’-type QW laser is demonstrated with the lasing wavelength at 2.35 μm at room temperature. However, some imperfections such like the localized states, the non-linear L-I curves and the low quantum efficiency are found in the experimental results. These issues will be discussed in this thesis. Third, we try to operate the laser with CW-injected current, but it does not lase due to the heating effect from the active region. To improve heat dissipation, the AuSn eutectic bonding technique is applied and the laser die is epi-side-down bonded on the AlN submount. Finally, the CW-injected laser is realized with the maximum output power of 0.92 mW at room temperature and it will be much more useful for the practical applications.