p 型鋰掺雜氧化鋅薄膜製程及電性研究

Fabrication and electrical properties of p-Type Li-doped ZnO Thin Films

邱國創(CHIU, KUO CHUANG)

指導教授 ： 簡朝和

國立清華大學/工學院/材料科學工程學系/博士(2013年)

https://doi.org/10.6843/NTHU.2013.00125

摘要

在此研究中主要為包含四個部分：首先以全始計算方法應用於p-type ZnO金屬氧化物中摻雜物，對其電性及p/n type的關連與學理的可行性進行探討，第二部分為鋰摻雜氧化鋅材料粉體合成與靶材製作上，運用軟性化學合成法之液態反應法合成所要的粉體，其最大的優點在於能獲得組成均勻，粒徑大小在一定範圍內(50~100nm)的粉末，且再現性極佳。而這類反應法的另一優點為：有可能研製一些僅在動力學上存在的晶相，可以解決固態反應合成法僅能研製一般熱力學上穩定才存在之晶相的問題，並解決微量添加時添加元素在本體得均勻性及合成相與化學鍵結的成分設計，在粉體合成能在400 ℃準確合成出0.05 to 0.8 mole % 鋰參雜氧化鋅粉體，並製作成靶材。
第三部份，利用直流脈衝濺鍍法(DC Pulsed sputtering)鍍製鋰摻雜氧化鋅膜層，探討製程參數對鋰摻雜氧化鋅光電性質的控制，目的在獲得穩定的鋰摻雜氧化鋅薄膜，在實驗中以二次離子質譜儀確認薄膜中Li元素含量及霍爾效應量測儀量測電性及p/n type確認，藉以分析製程參數對鋰摻雜氧化鋅膜層特性的影響，在0.2mole%配比粉體製作成三吋靶材，成功的在室溫下濺鍍出p-type 透明的氧化鋅薄膜, 其特性為膜厚 : 573nm，resistivity : 1.302 (Ω-cm)，mobility : 0.94 (cm2/V•s), carrier concentration : 5.08 ×1018 (cm-3)，transmittance : 95%，找出主要製程控制因子有基板溫度，Ar 氣體流速，與濺鍍功率等。最後經實驗證明較高的機板溫度使得Li參雜濃度下降，而p type特性變差。 同樣的在較高的Ar氣體流速的情況下，也使得Li參雜濃度下降, 但在較高的濺鍍功率下，Li參雜濃度上升，而使p type特性變佳.。
第四部份，運用電化學阻抗分析量測方法，利用等效電路模擬在鋰摻雜氧化鋅膜層結構中鋰存在於晶粒與晶界位置上，對鋰摻雜氧化鋅膜層電性與光學特性的影響。並找出穩定p type 鋰摻雜氧化鋅膜層中鋰含量與膜層製程參數，最後以p-n junction量測方法，以current-voltage I-V Curve 驗證，確實在0.1~0.3 mole%下鋰摻雜氧化鋅膜層可形成穩定的p type 膜層。

關鍵字

全始計算方法 ； 軟性化學合成法 ； 氧化鋅 ； 直流脈衝濺鍍法

並列摘要

This study mainly focuses on the fabrication and electrical properties of Li-doped ZnO thin film, which includes four parts: I. Feasibility study on application of Vienna abinitio simulation package to the doping effect in p-type ZnO. II. Synthesis of Li-doped ZnO powder by soft chemical routes and the target fabrication. III. Thin film deposition of Li-doped ZnO by DC pulsed sputtering and study on the fabrication parameters. IV. Study of the electrical and optical properties of Li-doped ZnO thin film by impedance measurement.
We first evaluated the feasibility of using the first principle method, namely Vienna abinitio simulation package, to study the doping effect in p-type ZnO by discussing the relationships between dopant and electrical properties or p/n type behavior of the doped ZnO material. With respect to the synthesis of Li-doped ZnO powder and target fabrication, we used solution-based soft chemical routes to obtain high reproducible, homogeneous particles in the size range between 50~100nm. This kind of solution-based synthetic method may generate dynamic-stabilized crystal phase while the solid state reaction route can only synthesize thermodynamic-stabilized crystal structures. It also provides more accurate control over the homogeneity of dopant and the composition design of crystal phase as well as covalent bonding. The Li-doped ZnO powder with 0.05 to 0.8 mole Li doping level was formed and made as a target for further use.
For fabrication of stable Li-doped ZnO thin film and to understand the effect and control mechanism of fabrication parameters on the electrical and optical properties, we utilized DC pulsed sputtering to deposit Li-doped ZnO thin film, secondary ion mass spectrometry to determine Li element content, and Hall effect instrument to measure the electrical properties and confirm the p/n type behavior. By using 0.2 mole% Li doped ZnO powder, we successfully obtained transparent p-type ZnO thin film at room temperature. The characteristics of this thin film are: film thickness, 573 nm; resistivity, 1.302 (Ω-cm); mobility, 0.94 (cm2/V•s); carrier concentration, 5.08 x 1018 (cm-3); transmittance, 95%. We found the major factors in fabrication process are temperature of substrate, flow rate of Ar carrier gas and sputtering power. As the temperature of substrate or the flow rate of Ar carrier gas increased, the doping concentration of Li decreased and led to a poorer p-type property. However, the higher the sputtering power, the richer the Li doping concentration, which enhances the p-type property.
We further applied the electrical impedance measurement to the study of Li doping effect. By simulating Li atoms existing in the grain or on the grain boundary with equivalent circuit, the influence of Li dopant on the electrical and optical properties of Li-doped ZnO thin film could be analyzed. Accordingly, the optimal Li dopant content and fabrication parameters for stable Li-doped ZnO thin films were found. In the final part of this study, we demonstrated Li-doped ZnO with Li doping level of 0.1 to 0.3 mole could form stable p-type thin film by characterization with current-voltage I-V curve for p-n junction measurement.

並列關鍵字

Vienna abinitio simulation package ； soft chemical routes ； ZnO ； DC Pulsed sputtering

參考文獻

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