Investigation of the crystallization mechanisms in indium molybdenum oxide films by vacuum annealing
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Ding-Fwu Lii Department of Electrical Engineering, Cheng Shiu University, Kaohsiung County 833, Taiwan, Republic of China (Received 27 May 2004; accepted 25 March 2005)
The crystallization mechanisms for potentially high mobility molybdenum-indiumoxide (IMO) film were studied. The crystalline IMO films were deposited on unheated glass substrates via high-density plasma evaporation, and subsequent vacuum annealing was performed at 150, 200, and 250 °C for 30 min. The results of x-ray diffraction and x-ray photoelectron spectroscopy and electrical properties suggested that the room-temperature crystallization was induced from the highest compressive strain, ••• O⬙i )• clusters and oxygen vacancies. The highest mobility caused by the charged (MoIn 2 of 75.8 cm /Vs obtained at 250 °C was due to the charged In–Mo+6–O clusters and strain relaxation with (222)/(440) orientation change.
I. INTRODUCTION
Transparent conductive oxide (TCO) films have been extensively researched 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 TCO most widely used for optoelectronic devices is tin-doped indium oxide (ITO), which offers 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, low-temperature deposition has become increasingly important due to the development of polymer substrates. However, films deposited at low temperature by dc and radio frequency (rf ) sputtering, electron beam evaporation, or pulsed laser deposition were frequently amorphous and exhibited with poor electrical properties.4–8 Attempts have been made to produce ZnO–In2O3 thin 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 a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0248 2030
http://journals.cambridge.org
J. Mater. Res., Vol. 20, No. 8, Aug 2005 Downloaded: 12 Apr 2015
Additionally, there have been few reports on the indium molybdenum oxide (IMO) films prepared at high substrate temperature (120–420 °C) using thermal evaporation10,11 and rf-sputtered processes,12 which exhibit high carrier mobility, enough free carriers, and good optical properties. However, the crystallization mechanisms of the IMO film have not yet been determined. In this study, a room-temperature crystallization IMO film was prepared via a high-density plasma evaporation (HDPE) technique. Moreover, vacuum annealing proposed the dependence of defects on the mobility and carrier concentration in In2O3-based IMO film
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