半極性與非極性氮化鎵之寬能隙材料及光電元件研究---子計畫二：半極性或非極性氮化鎵新穎奈米光子元件之研究

Abstract

本計畫主要目的在於使用非極性(non-polar)或半極性(semi-polar)氮化鎵奈米結構製作新穎的發光元件並研究其相關的光電特性。我們在三年期的計畫中配合其他子計畫將發展包括：非極性及半極性氮化鎵的磊晶技術、氮化鎵奈米結構製程等技術以及非極化或半極化氮化鎵電子能帶結構之理論模擬。非極性及半極性氮化鎵材料可以將原本具極化性之c-plane氮化鎵中的壓電場效應減少進而使發光效率增強，此外非極性及半極性氮化鎵在受到應力的影響之下，分裂的價電帶能階不僅使得其發光具有特定之極化方向，更使其垂直於c軸的電偶極矩增大兩倍，此特性將有助於降低半導體雷射的臨界電流與增強半導體中的光與物質交互作用。基於此非極性或半極性氮化鎵材料的特殊光學特性，本計畫的研究主軸可歸納為以下三項研究重點：(1)發展並製作非極性或半極性氮化鎵面射型雷射(2)製作非極性與半極性氮化鎵微共振腔以探討光和物質的交互作用(3)製作非極性氮化鎵單光子發射元件。在第一項研究重點中，我們已成功利用c-plane氮化鎵達成國際上第一個連續操作之電激發面射型雷射，因此在此研究領域上已具有國際競爭優勢，若能進一步導入非極性或半極性氮化鎵材料，勢必更能提升面射型雷射之元件特性。第二項非極性氮化鎵微共振腔則是著重於探討半導體中光與激子(exciton)之間的強耦合交互作用，進一步研究極激子(polariton)雷射與固態中的玻色-愛因斯坦凝聚現象。第三項則是利用非極性氮化鎵材料的優點，研究其製作成量子點、奈米共振腔及奈米柱之單光子特性。在發展本計畫的過程中，我們將配合其他子計畫進行非極性氮化鎵的磊晶成長與奈米結構製程技術，同時搭配電子能帶結構之理論計算，以求進一步了解光與物質在不同形態的奈米結構下之交互作用的特性，進而開發新穎發光元件。

The main objective of the project is to fabricate advanced light-emitting devices by using the non-polar and semi-polar GaN nanostructures and study the related optoelectronic characteristics. We will cooperate with other sub-projects to develop the epitaxial technique for the growth of non-polar and semi-polar GaN materials, the process technique for the fabrication of GaN nanostructures, and the theoretical simulation of electronic band structures for non-polar and semi-polar GaN nanostructures. Conventional c-plane GaN-based multiple quantum wells suffer from the spontaneous and piezoelectric field which separates the electron and hole wave function spatially and leads to low emission efficiency. Non-polar and semi-polar GaN-based materials can diminish or even eliminate Quantum Confine Stark Effect (QCSE) to improve the light emission efficiency internally. In addition, the strain-induced valence band splitting allows fixed polarized light emission and two-fold enhanced dipole oscillator strength perpendicular to the c-axis in non-polar and semi-polar GaN, which can provide a unique specific polarized output light emission and lower the threshold current of semiconductor lasers and improve the light-matter interaction in semiconductors. Based on the non-polar and semi-polar GaN materials, the specific objectives of this project include three parts: (1) Development and fabrication of non-polar GaN vertical-cavity surface-emitting lasers (VCSELs). (2) Fabrication and measurement of non-polar GaN microcavities and investigation of light-matter interaction. (3) Fabrication and measurement of non-polar GaN single photon emitters. In the first part of this project, we have successfully demonstrated the world-first continuous-wave electrically pumped c-plane GaN VCSELs. Therefore, we have had the competitive advantages in this research field in the world. If we could employ the non- and semi-polar GaN materials, the device performance of GaN VCSELs will be further improved. The second part of this project is to investigate the strong exciton-photon interaction in non-polar GaN microcavities and probe the characteristics of polariton lasers and Bose-Einstein condensation in solid-state system. The third part of this project is to study the non-polar GaN single photon emitters by using quantum dots, nanocavities, and nanorods. During the period of this project, we will cooperate with other sub-projects to achieve the growth and fabrication of non-polar nanostructures. Furthermore, combining with the theoretical calculation of the electronic band structures we will study the physical mechanisms of light-matter interaction in different non-polar GaN nanostructures and develop the advanced light-emitting devices.