新穎氧化鋅鎵鈦透明導電薄膜之特性分析與研究

Characterization and Investigation on the Optoelectronic Properties of Novel Ti-doped GaZnO Transparent Conductive Oxide Thin Films

吳聲佑(Shen-Yu Wu)

指導教授 ： 劉維昇

元智大學/電機通訊學院/光電工程學系/碩士(2013年)

https://doi.org/10.6838/YZU.2013.00234

摘要

近年來透明導電氧化物的應用已備受重視，因其具有高透光率與高導電率兩項重要特性，使其極適合廣泛應用於各類光電產品及顯示器之中。目前已廣泛使用之透明導電氧化物，如：氧化銦錫，因其材料內之銦元素屬於稀有元素，且價格昂貴，同時氧化銦錫在高溫操作下並不穩定；另一方面目前藍光LED半導體製程均使用ITO做為透明電極，但依舊存在許多問題如：電子濃度過低、導電性不佳等等。因此本計畫便提出以氧化鋅鎵鈦及其複合材料取代氧化銦錫之可能性，並對其做深入光電特性研究。
氧化鋅薄膜擁有顯著之C軸（0 0 2）優選方向及良好的鎢彩（wurtzite）結構，其內部電傳導仰賴其材料本身之氧空缺（oxygen vacancies）及間隙鋅（interstitial Zinc）原子之淺層受體能階（shallow donor level）所提供的帶電自由載子。未摻雜之ZnO薄膜其電阻值很高，與製備方法有關，但可藉由不同摻雜元素的取代來獲得額外的電子。故本研究將以鈦（Titanium）與鎵（Gallium）兩者之複合材料摻雜於高品質氧化鋅薄膜中，冀改善薄膜光電特性。本論文將使用射頻磁控濺鍍法沈積氧化鋅鎵鈦（Ti-doped GaZnO）薄膜，並於製程中改變濺鍍功率、沉積時間、反應氣體流量及基板溫度，研製最佳光電特性之薄膜。此外經由高溫熱退火後，Ti原子將取代鋅原子使得載子濃度提升。載子濃度的提高乃由於Ti4+與Ga3+取代了Zn2+或佔據ZnO晶格中的間隙所貢獻，除提供傳導電子外，亦是離子化之雜質散射中心（ionized impurity scattering centers），可能佔據晶格結構中之間隙位置而使晶格變形，導致電子遷移率下降。載子濃度的提升亦會造成 Burstiein-Moss 效應，預期可使薄膜除了呈現高導電特性外，且還有更短波長的吸收邊界。
實驗結果顯示，經RTA快速熱處理450 oC後之GTZO薄膜相較於未退火之薄膜，明顯提高其薄膜光電特性。最低電阻率達1.6#westeur024#10-4 Ω-cm、最高載子遷移率達8.5 cm2/V-s和最高載子濃度7.74#westeur024#1021 cm-3。最高平均光穿透率（波長350-800 nm）達91.0 %，能隙達3.5 eV。Figure of merit數值達36.9#westeur024#10-3Ω-1。此優良GTZO薄膜之光電特性將強化光電產業界對ZnO複合材料之應用與研究，並實踐ZnO複合材料薄膜廣泛應用於任何光電元件之最終目標。

關鍵字

透明導電氧化物 ； 氧化鋅鎵鈦 ； 薄膜 ； 摻雜 ； 射頻磁控濺鍍 ； 快速熱退火

並列摘要

Recently, the application of transparent conduction oxide（TCO）has drawn much attention because of its two important properties: High optical transmittance and conductivity. On the other hand, the most adopted semiconductor material for manufacturing the TCO of blue light emitting diode was ITO, but still with challenges of low carrier concentration and poor conductivity. The development of oxide compound semiconductor grows up rapidly and was very important. Therefore, this dissertation proposes the usage of Ti doped GaZnO（GTZO）composite material to replace the usage of ITO as n-type TCO and its composite materials for their superior photoelectric characteristics.
Zinc oxide film has a C-axis（0 0 2）preferred orientation and wurtzite structure, its internal electrical conduction rely on its own oxygen vacancies and interstitial zinc with shallow donor level free carriers. Undoped ZnO films has high resistance, and can be improved by substituting different doping elements to Zn2+ for providing an extra free electron. Therefore, this study doped titanium and gallium in high-quality zinc oxide thin films to improve the optoelectronic characteristics of TCO thin-film. In this study we using RF magnetron sputtering to deposit Ti-doped GaZnO film, and changing the sputtering power, deposition time, reaction gas flow rate and substrate temperature in order to develop the advantageous TCO film. In addition, through a high-temperature thermal annealing, Ti atoms replace zinc atoms make the carrier concentration to increase. The improvement of carrier concentration is found due to the replacement of Zn2+ by Ti4+ and of Ga3+ in ZnO lattice, and can not only provide a conduction electron, but also reduce the ionized impurity scattering centers. The enhancement of carrier concentration will lead to Burstiein-Moss effect with increased optical band gap, and can lead the GTZO TCO thin film with improved optical transmittance, and short-wavelength absorption band edge.
For the experiment results in this study, GTZO film with 450 oC post annealing can significantly improve its optoelectronic properties including lowest resistivity of 1.6 #westeur024# 10-4 Ω-cm, highest carrier mobility and carrier concentration of 8.5 cm2/Vs and 7.7 #westeur024# 1021 cm-3, respectively. The maximum average transmittance（wavelength 350-800 nm）reached 91.0 % along with the energy gap of 3.5 eV. Figure of merit value of 36.9 #westeur024# 10-3Ω-1 was obtained in this work. These excellent optoelectronic characteristics of GTZO films will be helpful in the device application with superior operation performances.

並列關鍵字

Transparent Conductive Oxide (TCO) ； Ti-doped GaZnO (GTZO) ； thin film ； doping ； RF magnetron sputtering ； RTA

參考文獻

[1]C.G. Granqvist, et al., Thin Solid Films, Vol. 411, p.p. 1, 2002.

[2]B. Park, et al., Solid State Sciences, Vol. 12, p.p. 1966, 2010.

[3]D. Song, et al., Appl. Surf. Sci., Vol.195, p.p. 291, 2002.

[4]J.L.Vossen, physics of thin films, Vol.9, p.p. 1, 1997.

[6]K.U. Sim, et al., Curr. Appl. Phys., Vol.10, p.p. 463, 2010.