半導體微共振腔內之耦合行為研究

Abstract

本論文旨於探討半導體微共振腔內之耦合行為，其主要研究內容涵蓋三個主題。首先，在論文的第一部份，我們以應力調變的方式來控制半導體量子點與微碟共振腔中模態的耦合行為。量子點中的激子與共振腔模態其能量因為對於外加的應力有不同的反應速率，所以可以藉此來達成共振。我們清楚地在譜線上觀察到了激子與共振腔模態之間的強耦合以及弱耦合行為。此種應力調變的元件可以在固定溫度下，雙向的調控激子的發光波長而不會顯著的影響其發光速率以及半寬。 在了解完單一量子點與共振腔模態的耦合之後，緊接著探討的是兩個微碟共振腔的耦合行為。利用兩個緊鄰的微碟共振腔所組合而成的光子分子來探討其強耦合行為。藉由連續的調變其中一個微碟共振腔的折射率，可以清楚的觀察到共振模態能量的反交叉以及其半寬的交叉現象。模態耦合理論幫助我們得到兩耦合模態間的耦合強度。並且藉由等效位能侷限電磁波的概念，我們清楚的解釋了在高階模態與低階模態間各自不同耦合強度的成因。 最後，為了能夠闡明微共振腔在空間上的場分布，我們利用掃描式近場光學顯微系統來研究微碟共振腔模態在空間上的分布。藉著光纖探針掃描，掃描式近場光學顯微技術可以獲得奈米等級的譜線資訊。此種技術可以偵測微碟共振腔以中特定模態在空間上的譜線分布。藉由知曉這些模態的空間分布情況，有利於進行後續的元件整合製成。

This dissertation investigates the coupling behaviors happened in microcavities. The main focus of this dissertation is divided into three parts. At first, we present the control of couplings between quantum dots (QDs) and cavity modes in microdisk (MD) microcavities by a stress tuning scheme. The excitonic transitions and cavity modes are brought into resonance due to their different energy shift rates with the applied strain. Spectral signatures of both strong and weak couplings are clearly observed. The strain tunable device can be used to tune the exciton wavelength bidirectionally at constant temperatures without significantly affecting the emission rate and linewidth of excitons. After demonstrating the couplings between single QDs and cavity modes, the couplings between two MD microcavities are discussed. Strong couplings between cavity modes in photonic molecules (PMs) formed by two preselected nearly identical MD microcavities with embedded QDs are investigated. By continuously tuning the refractive index of one MD, clear anticrossings in the resonant peak energies associated with crossings in the peak linewidths can be observed. The coupling strengths are extracted by the coupled mode theory and analyzed by the model which considering the effective potential confining the electromagnetic waves in the microcavities. At last, in order to clarify the spatial distribution in the microcavities, the spatially resolved characteristics of cavity modes in MD microcavities are investigated by near-field scanning optical microscopy (NSOM) system. The spectrally resolved NSOM technique acquires the emission spectra of nanoscale objects during fiber probe scanning. This technique enables us to detect the position-dependent spectra for a given mode in MD microcavitie. The resolved spatial distribution of cavity modes can provide us more precise locations for the further device integration processing.