寬能隙材料半導體平面型微共振腔雷射之研究

Abstract

平面型微共振腔雷射中，除了大家所熟知的垂直共振腔面射型雷射之外，也可以藉由光與物質強耦合產生的準粒子-極化子的玻色-愛因斯坦凝聚來產生極低閾值的同調光輸出，稱為極化子雷射。寬能隙半導體例如氮化鎵與氧化鋅由於具有與室溫熱擾動能量匹配的激子束縛能，在製作短波長的微共振腔雷射，包括垂直共振腔面射型雷射與極化子雷射上十分具有潛力。於此篇論文中，我們利用氮化鎵製作具有實用價值的電激發垂直共振腔面射型雷射更利用激子特性更強的氧化鋅材料以光激發的型式發展出極低閾值的極化子雷射。 透過數值分析，我們發現透明導電層與橫向的侷限孔徑在雷射閾值上扮演著很重要的角色。因此我們也提出了一個具有新型的回填式二氧化矽侷限孔徑的垂直面射型共振腔雷射設計，並以光激發的型式驗證了其雷射現象以及橫向光學侷限的效果。在電激發的元件中我們觀察到了二氧化矽孔徑的電流侷限效果，也在光譜上觀測到了橫模的產生。這兩個個現象都顯示了我們提出的結構可以有效的達成光學以及電流上的侷限。 接著我們利用氧化鋅微共振腔元件觀測到極化子的形成並觀測到極化子馳豫以及瓶頸效應的現象。接著利用高功率激發驅動極化子間的散射成功在室溫下觀察到極低閾值的極化子雷射。除此之外，我們亦發現藉由極化子可透過與光學聲子間的碰撞達到更有效率的馳豫並有效降低極化子雷射的閾值。這些研究成果對於未來設計氧化欣微共振腔極化子雷射提供了一個清楚的藍圖並驗證了氧化鋅在製作極低閾值的極化子雷射元件上的潛力。

In planar microcavities (MCs), beside the vertical-cavity surface-emitting laser (VCSEL) action, another low threshold laser could be generated by the Bose-Einstein condensation of cavity-polaritons, named polariton laser. Wide-bandgap materials including ZnO and GaN have a high potential on making VCSELs and polariton lasers due to their high exciton binding energies. In this thesis, we report an electrically injected GaN-based VCSEL and an optically pumped ZnO polariton laser. Through simulation, we found that transparent conducting layer and lateral confinement aperture play important roles on reducing lasing threshold of the GaN VCSEL. We also proposed a new low index aperture design for GaN VCSEL and observed a transverse mode lasing behavior by an optical pumping experiment. For the electrically pumped VCSELs, the proposed low-index SiO2 aperture can confine both the current and optical mode simultaneously, which reveals its confinement capability. For the ZnO-based MC, a clear formation of cavity polariton has been observed. And the corresponding poalriton relaxation and bottleneck effect were also verified. A low threshold polariton laser can be achieved by polariton self-interaction at room temperature. Besides, the polariton laser with a lower threshold can be achieved by assistant of longitudinal optical phonon-polariton scattering. These results provide a clear map for future designing of low threshold ZnO MC polarton lasers.