成長於非極化氮化鎵之寬能隙材料及光電元件研究---子計畫四：氮化鎵基光子晶體微腔型光源

Abstract

本計畫旨在於應用光子晶體結構，以強化氮化鎵基的藍、紫外光發光二極體 (LED)、微共振腔(Microcavity)發光二極體及雷射(LD)的出光特性。在光子晶體設計方 面，本實驗室具備三維的有限差分時域法(3D-FDTD)與平面波展開法(PWE)，可設計和優 化多種具有高Q 值的微共腔結構。在製程技術方面，本實驗室製作二維氮化鎵光子晶體 已有初步的成果，可完成光子晶體晶格常數約二至三百奈米，及蝕刻深度約在一百奈米。 第一年的研究工作，除了持續改進氮化鎵光子晶體製程，將著重在光子晶體微共 振腔的設計，並且整合光子晶體與藍紫外發光二極體的製程。利用光激發元件的特性量 測，以改良光子晶體微共振腔的設計。 第二年的研究重點將放在發展電激發元件之製程及其電性量測，控制電流侷限， 配合材料的出光波長與偏振以設計光子晶體微共振腔，是此階段發展的關鍵。 第三年本實驗室將致力於發展兩種前瞻性的光子晶體發光二極體元件，包括引進 布拉格反射鏡作為第三維之光子侷限，及利用量子結構作為主動元件的發光區。在布拉 格反射鏡方面，本實驗室已有相關的三維之微共振腔理論發表，然而磊晶與製程技術則 有賴與其他子計畫主持人的合作發展。在量子結構方面，因電子與光子同時受元件結構 所侷限，如設計得當，可大幅改進發光二極體出光特性。再者，此類元件亦有發展單光 子光源的潛力，因此在低溫的光激發特性量測上亦是研究的重點之一。

III-Nitride optoelectronic devices have become important in a wide variety of applications ranging from semiconductor lighting to medical surgeries, where the demand for blue and ultraviolet light emitting diodes or laser diodes has dramatically increased in recent years. Highly directional and coherent light emission can be achieved by employing photonic crystal (PC) microcavities. In this proposal, the development and characterization of GaN-based PC microcavity light sources are proposed. In our research lab, we can design and optimize PC microcavities using three-dimensional finite difference time domain (3D-FDTD) and plane wave expansion (PWE) methods. By sharing processing and characterization equipments with other research groups, we can fabricate and characterize the PC microcavity devices efficiently. Currently we are capable of fabricating two-dimensional photonic crystals with the lattice constant of 200nm to 300 nm and the etch depth of 100nm. We will continually improve the process of PC fabrication for high aspect ratio and applications in the ultraviolet wavelength range. In the first year of this three-year research proposal, we plan to develop the methodology to design PC microcavities and integrate the fabrication process of photonic crystals and light emitting diodes. The research objectives include the demonstration of microcavity effects in optically-pumped GaN LEDs, and the optimization of the PC microcavity designs. In the second year, we will focus on the development and characterization of electrically-injected devices. Current confinement and microcavity design for polar and non-polar GaN materials will become crucial issues at this stage. Well-designed epitaxial structures, device topology, and PC microcavities are key elements to achieve our research objectives. In the third year, we plan to develop advanced PC microcavity emitters. Two device structures are of particular interest. One is the introduction of Bragg mirrors as the photon confinement in the third dimension. The other is to employ quantum wells (QWs) or quantum dots (QDs) as the active region. For the former structure, we have developed theoretical calculations on the microcavity design. If well-designed, such emitter can exhibit very low threshold current due to 3D photon confinement. However, the complex epitaxy and device fabrication will be the challenges. For the latter structure, the device could potentially have very high efficiency due to both the optical and electrical confinements. Moreover, recent developments in single photon sources have exploited the structure of semiconductor quantum dots placed in a high quality-factor (Q) microcavity. Thus, low-temperature characterization of fabricated devices will also be performed to investigate the potential of PC-QD emitters as the light sources for quantum communication and quantum encryption.