原子層沉積技術成長氧化鋅鋯於透明導電氧化物薄膜之應用

Abstract

本研究主要探討與改善透明導電氧化物的光電性質，藉由兩種不同的原子層沉積技術在玻璃基板上製備氧化鋅鋯薄膜以達到一般光電元件所需要的等級。這些氧化鋅鋯薄膜的電性可達電阻6 × 10-4 Ω-cm、載子濃度1 × 1021 cm-3的程度。且一般原子層沉積在一次只通入一種反應前趨物去覆蓋表面產生化學吸附，但本研究中也使用另一種沉積方式，在一次循環反應裡連續通入兩種反應前趨物。比較兩種方式得到的透明導電薄膜，連續通入兩種前趨物可以讓兩者競相與表面官能基反應，分享所有可以反應的位置，藉此在同一層內有鋅與混摻材料鋯分佈其中，有效地讓額外混摻的鋯提供載子濃度。 除了電性外，本文亦使用光譜儀來量測光穿透度，本文中製備的透明導電薄膜不論在可見光或遠紅外光波段都有大於85%的良好光穿透率。市售的銦錫導電玻璃雖然在可見光範圍內的穿透率很好，廣泛應用於現今的電子裝置上，但其光穿透率於紅外光波段便迅速下降，然而我們的氧化鋅鋯薄膜並不會，除了薄膜主體材料的電漿頻率影響外，本文嘗試以混摻不同材料造成的鍵結間距改變來解釋薄膜於遠紅外波段的光穿透率差異現象。

This study investigates electrical and optical properties of Zr-doped ZnO (ZZO) films grown by atomic layer deposition (ALD), with the goal of developing transparent conductive films with high conductivity, high optical transparency throughout the visible and the near-IR region, and excellent gas-barrier property such that they can serve also as gas-diffusion barriers. Two ALD processes were studied: a conventional process where the Zr dopant is introduced by alternating ZnO layers with ZrO2 dopant layers, and a mixed-deposition process where ZnO layers are alternating with dopant layers composed of a mixture of ZnO and ZrO2. The mixed-deposition process resulted in a much lower resistivity than that of the conventional process, reaching 6 × 10-4 Ω-cm, owing to its removal of excess Zr content in the dopant layers, which improved doping efficiency of the dopants and minimized dopant-induced interference in the microstructure of the ZnO phase. The ZZO films showed excellent optical transparency, with transmission above 85% both in visible and in the near-IR region (wavelengths from 400 to 2100 nm), the latter of which was a significant improvement over the currently mainstream In2O3:Sn (ITO) films. The high near-IR transparency was attributed to the plasma frequencies of ZnO and In2O3 and the absence of dopant-induced bond stretching in the host material, thanks to the similar ionic radius of Zr to that of Zn. The ZZO films also showed excellent gas-barrier properties, with helium transmission rate down to 156 c.c./m2-day, as a result of the low-defect-density capability of ALD. Our results demonstrate that ALD ZZO films are a promising TCO option for applications such as flexible solar cells.