利用熱氣相沉積法成長氧化鋅相關奈米結構與其結構性質和光學性質之研究

Abstract

我們成功的利用熱氣相沉積法成長兩種型態氧化鋅奈米結構—氧化鋅奈米鋸子以及氧化鎂鋅奈米線。 在鋸齒狀的氧化鋅奈米結構研究中，我們以X光繞射,電子顯微鏡，以及拉曼光譜確定其為纖鋅礦結構的氧化鋅。在低激發功率的室溫光激發光光譜中，能量在3.22eV附近有很強的激子復合所產生的螢光，其寬度為150 meV；使用高功率密度的脈衝雷射激發，我們發現在3.18 eV附近有數個寬度小於4 meV的峰值產生。改變激發功率，激發面積以及偏振性的光激發光光譜，我們確認隨機雷射(Random lasing)的產生。 在ZnMgO奈米線的研究中，我們利用X光繞射，電子顯微鏡，以及能量散佈光譜儀推測其應該為ZnO為軸心，MgO包覆在外的奈米結構。隨著熱處理的溫度增高，激子相關的光激螢光光譜會從能量3.27 eV位移至3.5 eV。這是由於鎂與鋅在高溫會互相擴散，造就了三元的ZnMgO奈米線的生成，也因此達成了ZnMgO奈米線的能隙工程(Bandgap Engineering)。我們亦觀察到ZnMgO三元奈米線的光激發受激輻射的放光；此種優異的光學增益介質，非常具有做為奈米發光源的潛力。

We have successfully synthesized two types of ZnO nanostructures by a simple vapor transport method. XRD and TEM measurements indicate that the ZnO nanostructure is made of the single-crystal with wurtzite structure. For the nanosaws, the PL spectra were measured at room temperature. Under low excitation density, the emission shows an intensive peak at about 3.22 eV with FWHM~150 meV. This emission peak is attributed to the recombination of free excitons. As increasing excitation density, several sharp peaks emerge at around 3.18 eV with FWHM less than 4 meV. We measured emission spectra at different excitation areas while fixing the excitation intensity and polarization dependence of the emission that confirmed the random lasing action in ZnO nanosaws. On the other hand, ZnO/MgO core-shell structures were conjectured by XRD, SEM, EDS and TEM measurements. The optical properties of ZnO/MgO core-shell structures were analyzed by PL. After annealing treatment, the position of the NBE emission peak shifts towards higher photon energy from 3.27 eV~3.5 eV with increasing annealing temperature. A blueshift in the near band emission after annealing treatment is attributed to the diffusion of Mg into the ZnO nanowires to form ZnMgO alloy. Band gap engineering and stimulated emission of ZnMgO nanowires with different Mg doping are also demonstrated. The unique properties of stimulated emission in ZnMgO nanowires could be potentially utilized for nano-device applications.