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Title: | 原子層沉積成長之氧化鋅奈米薄膜之載子生命期 Carrier Lifetimes of Atomic-Layer-Deposition-Grown Zinc Oxide Nano Thin Films |
Authors: | Chao-Hsun Liu 劉昭勳 |
Advisor: | 孫啟光(Chi-Kuang Sun) |
Keyword: | 超快雷射,原子層沉積成長,氧化鋅,奈米薄膜,載子生命期, ultrafast laser,atomic layer deposition,zinc oxide,carrier lifetime, |
Publication Year : | 2012 |
Degree: | 碩士 |
Abstract: | 當提到氧化鋅這項材料時,人人無不提及其為未來近紫外光發光元件的潛在股,但事實上這並不讓人們意外:由於其能隙大小為3.4電子伏特,與當今最盛行的藍光LED原料──氮化鎵,幾乎如雙胞胎般的兩方相似。在過去的量測經驗顯示:氧化鋅薄膜在室溫量測下其載子生命期很短,平均而言是在數十個皮秒左右;然而在原子層沉積成長下的奈米薄膜卻發現約有上百皮秒。
因此,在本篇論文中,為了瞭解原子層沉積成長之奈米薄膜的載子生命期,以及進一步去推測與發光效率相關的載子放射結合生命期,我們準備了以藍寶石基片為基底而生之四種氧化鋅樣本:其一,有退火的氧化鋅薄膜;其二,無退火的氧化鋅薄膜;其三,有退火的氧化鋅薄膜覆蓋氧化鎂層;以及最後,無退火的氧化鋅薄膜覆蓋氧化鎂層。我們發現最後一組樣品因系統限制因素而無法最進一步討論,然而其他三組之載子生命期皆在上百皮秒。其中有退火的樣品表現較好,其載子生命期明顯長於沒退火的樣品;而覆蓋氧化鎂層的樣品其載子生命期則略短於無成長覆蓋層的樣品。若以雷射光子能量而言,當所有的樣品隨偵測光子能量增加,我們皆可以觀察到載子生命期減短的現象。若以偵測光的機制而論,這些觀察是合情合理的。 如果是針對各個樣品選定特定波長,並以不同的光引發載子濃度條件下去觀察樣品的載子生命週期,則可以發現有退火的氧化鋅薄膜幾乎維持定值;有退火的氧化鋅薄膜但覆蓋氧化鎂層的樣品則稍微隨濃度增加而減短生命期;沒有退火的氧化鋅薄膜則明顯隨濃度增加而生命期減短。以上這些觀察可能與載子再結合的眾多機制有關,更包含過程中各個機制所顯現的權重。經由觀察光引發載子濃度與其生命期,我們估計氧化鋅奈米薄膜的載子放射結合生命期,大約是六百皮秒。 When we mention the material “zinc oxide,” people always take it as a potential stock of near-ultraviolet light emitting devices in the future. Actually it is not a surprise for us: Because the bandgap energy of zinc oxide is 3.4 eV, and it is similar to the most popular material of LED growing, gallium nitride. Shown by the reports in the past, the carrier lifetime of zinc oxide thin film measured at room temperature is short, and it is about several tens of picosecond in average. However, we discovered that the carrier lifetime of zinc oxide nano thin film grown by atomic layer deposition, which has better thickness control than traditional deposition technique, is about hundreds of picosecond. In this thesis, for the purpose of understanding the carrier lifetime of zinc oxide nano thin films grown by atomic layer deposition, and further estimating the radiative recombination carrier time related to the luminescence efficiency, we prepared four kinds of zinc oxide thin films which grown on sapphire substrates: First, annealed zinc oxide thin films; Second, zinc oxide thin films without annealing; Third, annealed zinc oxide thin films covered by magnesium cap layers; and the last, zinc oxide thin films without annealing and covered by magnesium cap layers. We found that we cannot do further discussion about the last sample due to the carrier lifetime is compatible to laser period, and the carrier lifetimes of other three types are all hundreds of picosecond. Among all the samples, annealed samples have more uniform performance, and their carrier lifetimes are obviously longer than the samples without annealing. Samples which covered by magnesium cap layers have slightly shorter lifetime than samples without magnesium cap layers. In the aspect of the photon energy of probe lasers, we can observe the phenomenon that carrier lifetimes decrease when the photon energy of probe beams increases in all of the samples. These observations are reasonable because of the relation between the photon energy of probe beams and energy loss mechanism If we observe the carrier lifetimes of samples by same magnitude of energy above the bandgap energy, and under the conditions of different optically induced carrier densities, we can find that the carrier lifetimes almost maintain constant for annealed zinc oxide thin films. For the annealed zinc oxide thin films with magnesium cap layers, the carrier lifetimes slightly decrease when optically induced carrier densities increase. The carrier lifetimes of zinc oxide thin films without annealing obviously decrease with increasing optically induced carrier densities. The results above may be related to the mechanisms of carrier recombination, and the weight of each mechanism presents in the process. By observing the optically induced carrier densities and their lifetimes, we estimate that the radiative recombination carrier lifetimes of zinc oxide nano thin films grown by atomic layer deposition are about 600 ps. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/66409 |
Fulltext Rights: | 有償授權 |
Appears in Collections: | 光電工程學研究所 |
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