光電奈米材料與結構中激子之控制

Abstract

現代光子學研究的核心問題之ㄧ是控制光子與物質的交互作用。在過去十年間，為 了改進功能性量子光電子元件，電子狀態密度和局部的光子狀態密度(LDOS)的提升，已 經被利用來提高電子與光子之交互作用。尤其是將量子點 (QDs) 嵌入光子晶體 (photonic crystal, PhCs)，提升LDOS 來增強電子 ─光子交互作用，以便作為單光子 源；相反地，在一個減少的LDOS 環境裡，降低電子 ─光子交互作用也是可能的。PhC 是一種週期性交替折射率的結構，因為有可控制且很高的LDOS，是一個接近理想的實驗 平臺來研究增強與抑制電子 ─光子交互作用。相較於量子點在一個均ㄧ的媒介中，光 子晶體的能帶結構的 LDOS 可以調制嵌入的量子點電子 ─光子交互作用。 氧化鋅(ZnO)是屬於寬能隙的Ⅱ-Ⅵ半導體，室溫時它的能隙約為3.37eV;而且具有 相當大的激子束縛能(60meV，優於GaN 的25 meV)，因此在室溫下氧化鋅的螢光幾乎是 由激子所決定。另外ZnO 還有對高能量輻射忍受和穩定性及易濕化學法蝕刻，適合於太 空上之應用及可製作成小尺寸元件。而ZnO 奈米結構近年來已被應用在生物醫學、太陽 能電池、發光元件及光觸媒等領域。因此氧化鋅奈米結構是極佳的材料用來開發單光子 源、極化子雷射、太陽能轉換、和生醫感測等。 因為在ZnO 中有大激子束縛能和強電子-聲子藕合之優點，本三年計劃將逐一購置 單光子源偵測系統、叢集電腦(含第一原理計算軟體)和原子層沉積系統，用以完成單光 子源系統的建立、ZnO 量子點的理論計算及PhC 的成長來研究單光子發光和高溫凝態 Bose-Einstein Condensate；研究CuO 和Cu2O 之carrier multiplication 之行為，來 探討以ZnO(intrinsic n-type)奈米柱和CuO/Cu2O(intrinsic p-type)量子點製成全固 態太陽能電池之可行性，並研究其載子轉換之動態機制;以及ZnO 奈米材料與DNA 之表 面鍵結形成之表面態能階導致之發光機制。了解氧化鋅量子點UV PL 的發光機制及量子 點崁入光子晶體的動力學行之基礎科學研究對發展及未來應用在光電產業上。

One of the core issues of modern optics is the subject of photon interaction with matter. Over the past decades, quantum and photonic structures with increased density of electronic states and local density of optical states (LDOS) have been exploited to enhance the electron-photon interaction for improving functional quantum photonic devices. Embedded quantum dots (QDs) as single photon sources, in particular, promise to see large improvements, while, the reverse is also possible in an environment with a decreased LDOS. Photonic crystals (PhCs), periodic arrays of alternating refractive index, are near-ideal test beds for such experiments. Their electromagnetic band structure modifies the LDOS so that the optical properties of the embedded QDs as compared those in bulks (homogeneous media). Zinc oxide (ZnO) is a typical wide and direct gap II-VI compound semiconductor (bandgap energy Eg = 3.37 eV at room temperature). The binding energy of free exciton of wurtzite ZnO crystallizes is known to be very large (60 meV as compared to its counterpart GaN of 25 meV). Therefore, the free exciton can be even present at room temperature when it is photoexcited above the band gap or resonant to the free exciton energy level. Besides, there are additional properties which make ZnO preferable over other wide-band-gap materials-- its high energy radiation stability and amenability to wet chemical etching making it a very suitable candidate for space applications providing an opportunity for fabrication of small-size devices. The ZnO nanostructure has recently been applied in biomedicine, solar cell, LED and photocatalyst. Therefore, the ZnO nanostructure is an extremely good candidate for pursuing single photon source, polariton laser-- Bose-Einstein condensates, solar energy conversion , and biosensing. With the merit of large exciton binding energy and strong electron-phonon coupling in ZnO, in this three proposal, we plan to purchase and to establish a single photon source detection system, PC-cluster (including first principle computation software) and Atomic Layer Deposition system for growing heterostructures as well as PhCs. We wish ZnO would have potential for exploring single photon emission and for achieving BEC at the higher temperature. These results may benefit both fundamental photonic study and photonic industrials.