化合物半導體微共振腔偏極化激子之光電研究

Abstract

本計劃為一新提三年計劃，我們將探討光與物質作用下所形成之微共振腔極化激子(microcavity polariton)及 indirect excitons in coupled quantum wells之特性，並探討其形成波色－愛因斯坦凝聚態之可能性(Bose-Einstein Condensation)。微共振腔極化激子及Indirect Excitons均是目前最被看好可於數K 之溫度下形成固態BEC。微共振腔極化激子係因半導體量子井內激子與共振腔光子耦合成為等效質量極小之半光/半物質Quasi-particle，而Indirect Excitons則是因電子與電洞分別在不同但又耦合之半導體量子井內，生命期大幅增長之故。我們將使用MBE長晶系統成長微共振腔結構及coupled quantum wells並製作測試元件。量子井激子發光波長與微共振腔模態之detuning 將是實驗重要參數，嘗試在低溫下與pumping 配合找到形成固態BEC之條件。我們會特別注意大角度圓環狀之輻射及其近場coherent 特性，並觀察其是否有臨界點及特定之光偏振態出現。這些特性都是與BEC波函數直接相關，故可以其作為BEC出現之重要檢驗依據。以我們過去在VCSEL 及相關coherent patterns 多年之經驗，相信必然可在microcavity polariton及Indirect Excitons方面獲得不錯之成果。

In this three-year proposal, we will study the possibility of realizing Bose-Einstein Condensation of exciton polaritons in microcavity and also in coupled quantum wells. Exciton polaritons are half-matter and half-light bosonic quasi-particles formed in microcavities as a result of strong coupling between the excitons and cavity modes. The extremely steep dispersion of the cavity polariton modes, due to the optical confinement along the z direction, results in a typical polariton effective mass of 1/10000 times the free electron mass. Thus, in theory, the temperature and density criteria for BEC of polaritons in their ground state should be satisfied much more easily than for excitons. It is expected that the coherence, polarization and population distribution properties of polaritons can be probed by analyzing the far field and near field emissions, for the light emitted by the microcavity is part of the polariton wave function. It is also well known that optical microcavity and vertical cavity surface emitting lasers (VCSELs) basically share similar structures. Based on previous experiences in the study of the coherent emission patterns from broad area VCSELs, we have confidence that high quality results can be generated from this project.