氧化鎂鋅:鋁薄膜應用於氮化鋁鎵接觸之特性研究

Characterization of Al doped MgxZn1-xO thin film and theirs contact to AlGaN application

陳鼎堯(Ting-Yao Chen)

指導教授 ： 劉代山

共同指導教授 ： 李欣縈(Hsin-Ying Lee)

國立虎尾科技大學/電機資訊學院/光電與材料科技研究所/碩士(2008年)

摘要

本研究利用磁控式射頻共濺鍍系統(RF magnetron co-sputtering
system)，濺鍍氧化鎂鋅與共濺鍍氧化鎂鋅:鋁薄膜，進行光電特性分析及實際應用，探討透明導電膜與半導體間之接觸特性。在論文中的第一部份是利用濺鍍系統於藍寶石基板上製備不同鎂含量之氧化鎂鋅薄膜(MgxZn1-xO,x=0、0.1、0.2 及0.3)以及同時濺鍍氧化鎂鋅與鋁靶材之氧化鎂鋅:鋁薄膜，並藉由熱處理製程，觀察薄膜光電特性與材料特性分析。研究中，分別使用霍爾量測(Hall measurement)系統量測其薄膜導電特性，利用紫外線-可見光光譜量測儀(UV-VIS spectrometer)量測薄膜之光學特性，藉由薄膜之光學
特性分析薄膜之光學能隙，並且使用X 光繞射(XRD)分析及能量散佈光譜儀(EDS)分析薄膜結晶特性與微觀組織成份分析。由第一部分研究結果顯示，藉由適當的熱處理確實可有效降低薄膜電阻率， 但由於熱處製程並未能達到預期之目標，因此為了近一步提昇薄膜導電特性，故本研究利用氧化鎂鋅與鋁靶材共濺鍍，藉由適當的鋁原子摻雜，以有效降低於室溫沉積氧化鎂鋅薄膜電阻率。其最佳化射頻功率為固定氧化鎂鋅靶材濺鍍功率為100W 搭配其最佳鋁靶材濺鍍功率，在不同鎂含量分別為x=0(Al:20W)、x=0.1(Al:25W)、x=0.2(Al:30W)及x=0.3(Al:35W) ，即可獲得最佳導電特性之氧化鎂鋅:鋁薄膜，而不同鎂含量薄膜電阻率分別為1.55×10-3 Ωcm (x=0)至3.34×10-2 Ωcm (x=0.3)，經由鋁原子摻雜確實可使氧化鎂鋅膜薄導電特性提升。在光學特性方面氧化鎂鋅:鋁薄膜平均穿透率均可達80 %以上，由於鋁原子的摻雜也使得薄膜光學能隙更為提昇。氧化鎂鋅:鋁薄膜，其不同鎂濃度x=0、0.1、0.2 及0.3 的光學能隙分別為.55 、3.75 、4.27 及4.59 eV由以上趨勢說明成功製備高光學品質氧化鎂鋅:鋁薄膜，也由此可證實藉由鎂原子與鋁原子摻雜可有效提高能隙，使薄膜吸收邊界朝向更低紫外光波段。
在研究第二部份故製作了MgxZn1-xO:Al/n-GaN、MgxZn1-xO:Al/n-AlGaN等結構以形成歐姆接觸(Ohmic contact) 作透明導電材料的應用。實驗中也利用熱處理的方式，以試圖提升氮化鎵及氮化鋁鎵歐姆接觸處特性。經本論文的研究氧化鎂鋅:鋁薄膜，確實可藉由鎂含量的調整，得到寬能隙的薄膜，適當的鋁原子摻雜也有效的提昇薄膜導電特性與氮化鎵基板形成良好的歐姆接觸。一般應用於紫外光發光二極體的透明導電層大部分是利用氧化鋅透明薄膜，因此未來也可將氧化鎂鋅:鋁薄膜應用於紫外光發光二極體中，以減少紫外光被透明導電層吸收，以增加紫外光發光二極體的出光率。

關鍵字

氧化鋅 ； 氧化鎂鋅 ； 鋁

並列摘要

Transparent conducting oxides(TCO’s) are characterized by a unique combination of low electrical resistivity and high optical transparency. Zinc oxide has recently gained much interest because of its potential use in many
applications, ranging from transparent electrodes in light emitting diodes, solar cells, photodetectors, thin film gas sensors, spintronic devices, surface acoustic wave devices, and flat-panel display devices, attributed to its wide direct band gap,excellent chemical and thermal stability, and specific electrical and optoelectronic property with a large exciton binding energy. A TCO with a wider band gap can improve the efficiency of UV or blue light emitting devices when used as a transparent electrode.The band gap of ZnO can be controlled by alloying with MgO.In this work, we propose the use of band-gap modified Zn1−xMgxO as transparent conducting films.
In this study, the characteristics of MgxZn1-xO and MgxZn1-xO:Al thin films were deposited by using radio frequency magnetron co-sputtering system have been investigated. The performances of the transparent conductive thin film
contacted with semiconductors were also investigated. This thesis was divided into two parts, first part, MgxZn1-xO (x=0, 0.1, 0.2 and 0.3) thin films were deposited and MgxZn1-xO:Al thin film by co-sputtering system with MgxZn1-xO and aluminum targets on sapphire substrates at room temperature. Second part, MgxZn1-xO:Al thin films contacted with GaN and AlGaN. First part, the effect of post-annealing on photoelectric and material haracteristics of MgxZn1-xO thin films was investigated. The detailed deposition conditions were base pressure 4×10-6 torr, sputtering gas ambient Ar 10sccm,sputtering pressure 10mtorr, RF power supplied to MgxZn1-xO(x=0~0.3) targets 100W, thin film thickness fixed 200nm. The electrical characteristics, opticalproperties, Crystallization and chemical composition of the thin films were analyzed by Hall measurement, ultraviolet visible spectrometer (UV-VIS spectrometer), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS), respectively. The minimum resistivity of MgxZn1-xO thin films were obtained by annealing at 900oC for 1min in nitrogen atmosphere by using rapid thermal annealing (RTA) system. MgxZn1-xO thin films were doped suitable aluminum atom in order to increase conductivity. The optimization RF power of 100 W was supplied to MgxZn1-xO target, and RF power of 20W (x=0), 25W (x=0.1), 30W (x=0.2), 35W (x=0.3) was supplied to aluminum target, respectively. The resistivity of MgxZn1-xO:Al(x=0~0.3) thin film were 1.55×10-3 Ωcm (x=0) to 3.34×10-2 Ωcm (x=0.3) , respectively, through the aluminum atoms doped MgxZn1-xO thin film can increase conductive effective.The transmittance of MgxZn1-xO:Al film has over 80 % in visible light region. The optical band gap were also determined by the transmittance spectra, which increased from 3.55 eV at (x=0) to 4.59 eV at (x=0.3). Second part, the structures of MgxZn1-xO:Al/n-GaN and MgxZn1-xO:Al/n-AlGaN were deposited to form the ohmic contact, that were achieved with thermal annealing. We will explore TCO with semiconductor contact characteristics. The current-voltage (I-V) characteristics were measured using an HP4156 semiconductor parameter analyzer. Specific contact resistance, ρc, was calculated by measuring the resistance versus the distance between TLM pattern.In present research, MgxZn1-xO:Al thin film could obtained the width optical energy bandgap by Mg content adjustment, the suitable aluminum atom doping also promotion thin film electric conduction characteristic effectively. A transparent conducting oxide with a wider band gap can improve the efficiency of UV or blue light emitting devices, so MgxZn1-xO:Al thin films will application in LED in the future.

並列關鍵字

ZnO ； MgxZn1-xO ； Al

參考文獻

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