利用原子氣相沉積技術成長摻雜鋯與摻雜鎂之氧化鋅研究

Abstract

氧化鋅（Zinc Oxide, ZnO）為近年來相當引起矚目的半導體材料。由於其具有很大的激子束縛能（~ 60 meV），使得氧化鋅於室溫下仍具有良好的激子復合發光之特性。本論文探討使用原子氣相沉積技術（Atomic Layer Deposition, ALD），分別成長摻雜鋯以及摻雜鎂之氧化鋅薄膜，並進行相關特性之研究。 摻雜鋯之氧化鋅（Zirconium-doped ZnO, ZZO）為一具有潛力之透明導電薄膜材料（transparent conductive oxide, TCO）。利用ALD沉積之ZZO薄膜具有低電阻率(1.3×10-3 Ω-cm)、高載子濃度(2.2×1020 cm-3)，以及可見光波段具有高穿透度(>92%)等特性，因此ZZO被視為有希望取代ITO之透明導電膜材料；另外，本篇論文中也會探討ZZO薄膜的光激發光（photoluminescence, PL）以及受激發光（stimulated emission）等光學之行為。由PL頻譜可以看出，ZZO薄膜於380nm波段具有相當強的自發性發光(spontaneous emission)，且PL頻譜將呈現近乎無缺陷（defect-free）的狀態；另外，室溫下ZZO具有相對低之雷射閥值（約為105 kW/cm2）。 論文另一部分在討論摻雜鎂之氧化鋅（Magnesium-doped ZnO, MgZnO）之特性。使用ALD技術成長不同摻雜濃度之MgZnO薄膜，經過高溫快速退火處理後可發現，MgZnO的能隙值可藉由調控鎂之摻雜比例而改變，此即為所謂的能隙工程（bandgap engineering）。而當鎂的含量越多，MgZnO之吸收邊緣（absorption edge）和光激發光波段將會往相較於ZnO之更短波長方向藍位移（blueshift），且其激子束縛能也將隨之增加。另外，MgZnO之受激發光波段也明顯的往短波長方向偏移，且具有相當低之雷射閥值（lasing threshold）。這些優點將有助於MgZnO成為下個世代藍紫外光波段發光元件之材料。 最後，我們使用ALD技術製作氧化鋅鎂�氧化鋅之異質結構（MgZnO�ZnO heterostructure）。由於受到量子尺寸效應（quantum size effect）的影響，當覆蓋在MgZnO表面之ZnO層為2nm時，ZnO發光波段將會明顯的偏移至373nm，且其激子束縛能將會大幅地增加至120meV。

Recently, ZnO has gained substantial interest for ultraviolet (UV) light-emitting devices because of its large exciton binding energy up to 60 meV. In the thesis, we present the electrical and optical properties of zirconium-doped zinc oxide (ZZO) and magnesium-doped zinc oxidethin films grown by atomic layer deposition (ALD). Zirconium-doped ZnO (ZZO) is a suitable material for transparent conductive oxide (TCO). The ZZO films prepared by ALD showed low resistivity(1.3×10-3 Ω-cm), high carrier concentration(2.2×1020 cm-3), and high transparency (>92%) in the visible spectrum. As a result, ZZO is considered to be a promising substitute for ITO films. Photoluminescence (PL) spectra consisted of a strong spontaneous emission associated with the near-band-edge emission at 380 nm and a negligible defect-related band. The optically pumped stimulated emission in ZZO films was achieved with a low threshold intensity of 105 kW/cm2 at room temperature. The other part of the thesis reports the characteristics of magnesium-doped ZnO (MgZnO). For MgZnO films grown by ALD, the bandgap energy can be tuned by the Mg concentration and the post-deposition rapid thermal annealing. As the doping of Mg content in the ZnO films increased, the absorption and PL spectra blueshifted toward the shorter wavelength. The exciton binding energy in MgZnO films was enhanced as compared with that of pure ZnO films. The stimulated emission in MgZnO films also exhibited a blueshift and a low threshold intensity. As a result, MgZnO is applicable to the next-generation UV photonic devices. A 2 nm thin ZnO layer was deposited upon the MgZnO films to fabricate the MgZnO�ZnO heterojunction. Owing to the quantum confinement effect, significant blueshift in the PL spectrum toward 373 nm coupled with the remarkable enhancement of the exciton binding energy up to 120 meV were observed in this 2 nm ZnO film.