Zr-doped ZnO by atomic layer deposition for transparent conducting oxide films
Date Issued
2012
Date
2012
Author(s)
Yu, Pei-Wei
Abstract
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.
Subjects
Zr
ZnO
atomic layer deposition
transparent conducting oxide
ALD
Type
thesis
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