Properties of indium molybdenum oxide films fabricated via high-density plasma evaporation at room temperature
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Ding-Fwu Lii Department of Electrical Engineering, Cheng Shiu University, Kaohsiung County 833, Taiwan, Republic of China (Received 12 August 2004; accepted 25 October 2004)
The goal of this study was to determine the scattering mechanisms and investigate the optoelectronic properties of indium molybdenum oxide (IMO) films. IMO films were deposited from an In2O3/MoO3 target with a weight ratio of 99/1, 95/5 and 90/10 via high-density plasma evaporation at room temperature. Based on the structural, electrical and optical properties, this study proposed that the neutral complex x dominated at high doping content and high oxygen content, whereas [(2Mo•In)O⬙] i ••• • O⬙] dominated at low doping level or low oxygen content. ionized complex MoIn i Uniform 99/1 IMO films with minimum resistivity of 3.56 × 10−4 ⍀ cm (corresponding to a mobility of 14.6 cm2V−1s−1 and carrier concentration of 14.3 × 1020 cm−3) and average visible transmittance of ∼85% were produced at an optimum oxygen content of ∼9%. Average optical transmittance exceeding 80% was demonstrated, and a structural change appeared at low oxygen contents.
I. INTRODUCTION
Transparent conductive oxide (TCO) films have been extensively studied because of their numerous potential applications, such as flat panel display, solar cell, low emissive and electro-chromic windows, and thin-film photovoltaics.1–3 The most widely used TCO in optoelectronic device applications is tin-doped indium oxide (ITO), which offers a commercially acceptable performance in terms of conductivity, transmittance, environmental stability, reproducibility, and surface morphology. Most high-quality ITO films were either deposited at a relatively high substrate temperature of 300–400 °C via direct current (dc) magnetron sputtering or fabricated at room temperature and then annealed at 200 °C. Recently, due to the development of polymer substrate, lowtemperature deposition has become increasingly important. However, films deposited at low temperature by using dc and radio frequency (rf) sputtering, electron beam evaporation, or pulsed laser deposition were frequently amorphous and had poor electrical properties.4–8 Attempts have been made to produce ZnO–In2O3 thin
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Address all correspondence to this author. e-mail: [email protected] DOI: 101557/JMR.2005.0031 J. Mater. Res., Vol. 20, No. 1, Jan 2005
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films at low temperature to improve both the electrical and optical properties due to its high mobility.9 The TCO films with high mobility are well known as a convenient model for increasing conductivity and reducing freecarrier absorption.2 Indium molybdenum oxide (IMO) films with good opto-electronic properties have been previously reported to exhibit high mobility.10,11 However, these IMO films were fabricated at high substrate temperature of 350 °C via thermal evaporation,10,11 rf sputtered processes at 420 °C12 or 500 °C,13 and pulsed laser deposition at 500 °C.14 This work proposed a low-temperature (room temperature; RT) fab
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