以原子層沉積技術製備多功能摻鋁氧化鋅薄膜於具奈米結構矽基板上之特性研究

Abstract

本實驗利用原子層沉積系統於矽基板上成長多功能性摻鋁氧化鋅薄膜，實驗分為四階段：第一階段的實驗中，利用ALD系統，結合氣流中斷法及臨場摻雜法，使用Si(100)基板於280°C下成功成長出高品質氧化鋅及摻鋁氧化鋅薄膜。薄膜X光繞射結果為高優選ZnO(002)結晶取向，X光反射圖譜中，顯示ALD系統可以精準控制薄膜厚度，180 cycles (cy)及360 cy為45、90 nm。霍爾結果指出AZO 1:6薄膜有較低的片電阻，180 cy及360 cy分別為176、54.4 ohm/sq.，電阻率均為10-4 ohm-cm的數量級，光致螢光光譜顯示無鋅氧缺陷產生。橢圓光譜量測中，氧化鋅及摻鋁氧化鋅薄膜折射率均為1.8左右，紫外光可見光光譜結果指出， 沉積180 cy的薄膜於矽基板上時，λ=350~1100 nm範圍內，整體反射率都在30 %以下，沉積360 cy的薄膜於矽基板上時，λ=600~700 nm的範圍內為反射率最低值區間，都低於5 %。 第二部分為接面性質研究，電性較好的AZO 1:6薄膜有較高的turn-on電流，也有最佳光電轉換效率，45 nm和90 nm的薄膜厚度下，最佳為6.47x10-3 %和0.0187 %。 第三部分利用金屬輔助化學蝕刻法，濺鍍30秒的金作為催化劑製備矽奈米結構，結構極為準直，無交叉的情形。蝕刻時間1分鐘有高度約100 nm且準直的奈米結構出現，3分時達1 µm，5、7、10分別為2.2 µm、4.2 µm、7.5 µm，15分鐘時，結構高度可達13 µm。接著披覆厚度45 nm和90 nm的AZO1:6薄膜於奈米結構，SEM結果指出，薄膜均可完整的披覆在不同蝕刻時間的奈米結構上，UV-VIS光譜中，蝕刻時間從3~15分鐘的範圍內，披覆45 nm和90 nm的AZO 1:6薄膜於奈米結構上，λ=300~1100 nm範圍均有極低反射率，約在10 %左右。受蝕刻產生缺陷所影響，45 nm和90 nm薄膜披覆於結構上，整流特性不佳。在光伏結果上，厚度45 nm的AZO 1:6薄膜效率約10-4 %，甚至量測不到光電流，厚度90 nm薄膜的效率約10-3 %。 最後第四部分利用Essential Macleod軟體模擬AZO 1:6薄膜於矽基板上的光學特性，厚度數百奈米的AZO 1:6薄膜披覆在矽基板上時，有建設性及破壞性干涉條紋出現。但在厚度50~100 nm時，反射率在5%以下的區域能落在可見光波段附近，在此範圍內有極高的光吸收效果。進一步模擬ITO薄膜披覆在矽基板上的反射率圖譜，並與AZO 1:6反射圖比較，在膜厚50~100 nm的可見光範為內，AZO 1:6薄膜具有較寬的低反射率區域。由於AZO 1:6薄膜比ITO有更低的可見光反射，且可將抗反射區延伸到近紅外光，在45 nm、90 nm時，AZO 1:6薄膜平均反射率為20.11 %、14.95 %，比ITO的23.51 %、19.63 %低。

In this study, multifunctional AZO thin films were grown on Si(100) substrate by atomic layer deposition (ALD) system. The experiments contain four parts: At first, high quality ZnO and Al-doped ZnO (AZO) thin film was successfully deposited on Si(100) substrate grown by ALD system at 280°C which combined with flow-rate interruption method and in-situ doping technique. X-ray measurement showed that thin films were ZnO(002) highly-preferred orientation and precise thickness control by ALD which thickness of 180 cycles (cy) and 360 cy were 45 and 90 nm respectively. Hall and PL results indicated that the sheet resistance of 180 cy and 360 cy were 176 and 54.4 ohm/square, as well as resistivity were 10-4 ohm-cm without zinc or oxygen defects. We obtained the refraction index 1.8 of ZnO and AZO by ellipsometry. The UV-Vis spectrum showed that the reflectivity of 180 cy films coated on Si(100) substrate atλ=350~1100 nm were lower 30 % and 360 cy films coated on Si(100) substrate atλ=600~700 nm were lower 5 %. Second, AZO 1:6 thin films with better electrical properties coated on Si(100) substrate had higher turn-on current, and photoelectric conversion efficiency (PCE) of film thickness 45 nm and 90 nm were 6.47x10-3 % and 0.0187 %. Third, sputtering 30 seconds Au as catalyst, the well-alignment and no cross silicon nanostructure were prepared by metal assisted chemical etching method. At etching time 1 and 3 min, the nanostructure with length 100 nm and 1 µm were appeared, and grown to 2.2, 4.2 and 7.5 µm at etching time 5, 7 and 10 min. Moreover, at etching time 15 min, the structure length was able to achieve 13 µm. SEM images showed that 45 and 90 nm AZO 1:6 films were coated on nanostructure completely by using ALD system. The UV-Vis spectrum indicated that deposited 45 and 90 nm AZO 1:6 films on nanostructure with etching time 3~5 min exist low reflectivity about 10 % at λ=300~1100 nm. Due to defects effect, 45 nm and 90 nm AZO 1:6 films coated on nanostructure without outstanding rectifying properties had PCE 10-4 % and 10-3 %. At last, using Essential Macleod software simulated optical properties of AZO 1:6 films on silicon substrate. When thin film up to hundreds of nanometer thickness coated on silicon substrate, we could find constructive and destructive interference fringes. But when film thickness between 50~100 nm, high absorption and lower reflectivity zone were in visible light. Furthermore, simulated optical properties of ITO films on silicon substrate and compared to AZO 1:6 films. AZO 1:6 films with thickness 50~100 nm had broader low reflectivity zone, lower visible light reflectivity and higher IR absorption. And 45 and 90 nm AZO 1:6 films had lower average reflectance 20.11 % and 14.95 % than 23.51 % and 19.63 % of ITO.