氧化鋅微共振腔之極化子雷射之研究

Abstract

在微共振腔主動層中的激子(excitons)與其腔中共振的光子強烈耦合，當達到強耦合(strong-coupling)的狀態時，將會產生新的混合準粒子，稱之為極化子(polaritons)。極化子是一種混合光與物質特性的新粒子，其擁有特別且可調的色散曲線。近年來的研究發現，這些在半導體微共振腔的極化子有強烈的非線性散射和玻色子特性，完全不同於一般所熟悉的激子。這些特性可能達成極化子凝聚的自發性放射，產生極化子雷射。而極化子雷射不像傳統雷射需要達到居量反轉的閥值條件。在這篇論文中，我們有系統的研究並逐步的驗證及觀察在氧化鋅微共振腔之極化子雷射的特性。 首先，在室溫下利用變角度光激螢光量測系統觀察下極化子的色散曲線，其與利用轉移矩陣法所模擬的曲線相當吻合，也因此證明了極化子的存在。 再藉由增加激發光功率，以增加極化子與極化子間的散射，使得下極化子能有效的弛豫到基態，當載子密度達到波色最終態誘發散射之閥值時，下極化子大量佔據基態，並藉由自發性放射發出同調光。進而量測並探討極化子雷射在偏振態、空間上分佈的情形及空間同調性上的特性。 最後，我們也在同一樣品但不同區域上觀察到的傳統光子雷射，並以此與極化子雷射做對照，比較他們在色散曲線和極化特性的差異。

Microcavities containing excitons that couple strongly to photon can enter a regime of strong coupling which produces new mixed quasi-particles, the polaritons. Polaritons are half-light and half-matter particles, and possess unique and tunable dispersion relations. Recently, the discoveries in semiconductor microcavities have been shown that these polaritons differ completely from excitons in their enormous nonlinear scattering cross-sections and their bosonic statistics. This can lead to polariton lasing, the spontaneous emission of coherent light by condensates of exciton-polaritons. Unlike conventional lasers, polariton lasers have no threshold condition linked to the inversion of the population. In this thesis, a systematically study the characteristics of polariton lasers in ZnO-based Microcavities has been obtained. First, by using angle-resolved photoluminescence measurement, dispersion curves of polariton at room temperature are observed. These experimental results agree with simulated ones from transfer matrix method. That is an evidence of the existence of polaritons. As pumping power increases, lower polaritons efficiently relax toward ground state as a result of the increase of polariton-polariton scattering rate. When the carrier density reaches the threshold of bosonic final state stimulated scattering, lower polaritons macroscopically occupy ground state and spontaneously emit coherent light. Furthermore, we measure polarization, real space distribution, and spatial coherence in order to study the characteristics of polariton laser. Finally, we also observe the photon lasing at different region. By comparing polariton lasers with photon lasers, the clear discrimination of dispersion curves and polarization have been shown.