MOCVD route to In2O3 thin films on SiO2 substrates

Abstract

Indium oxide (In2O3) film is a technologically important transparent semiconducting oxide material and thus used in various fields such as photovoltaic devices, transparent windows in liquid crystal displays, sensors, and antireflection coatings [1–3]. In2O3 films can be prepared by a wide range of deposition techniques such as evaporation [4, 5], sputtering [6–8], spray pyrolysis [9], and ultrasonic spray chemical vapor deposition (CVD) [10]. Additionally, for the metal organic CVD (MOCVD) growth, various precursors such as trimethylindium (In(CH3)3) [11, 12], indium 2,2,6,6-tetramethyl-3,5-heptanedione (In(thd)3) [11, 13], and indium acetylacetonates (In(acac)3) [14, 15] have been employed. In this letter, we report the growth of In2O3 films on SiO2 substrates using a simple reaction of a triethylindium (TEI) and oxygen (O2) mixture. We investigate the effect of deposition temperature on the structural properties of thin films. The SiO2 layer was thermally grown on the Si (0 0 1) with a thickness of 60 nm. The SiO2/Si substrate was cleaned in acetone and then rinsed by deionized water. A schematic diagram of the MOCVD reactor used in our experiments was previously reported [16]. High-purity Ar (99.999% purity) passed through the TEI bubbler and delivered TEI vapor to the reactor. The TEI bubbler was maintained at a temperature of 35 ◦C. The In2O3 film was synthesized by supplying O2 and Ar carrier gases, respectively, with the flow rate of 5 sccm (standard cubic centimeters per minute) and 20 sccm. The deposition was carried out for 20 min and the substrate temperatures used in the present work were 200, 250, and 300 ◦C. The crystalline structure of the films was examined by X-ray diffraction (XRD) analysis on the θ–2θ geometry using the CuKα line. The structural morphology was characterized by scanning electron microscopy (SEM). Fig. 1 shows the XRD spectra of the as-deposited film at substrate temperatures in the range of 200–300 ◦C. Apart from the Si(0 0 4) diffraction peak, the θ–2θ scan data from the deposits at 300 ◦C exhibit a strong and sharp peak at 30.58 ◦, corresponding to (2 2 2) diffraction peaks of cubic bixbyite In2O3 phase (JCPDS 441087). Fig. 1a indicates that although we observe a very weak (2 2 2) diffraction peak corresponding to the In2O3 structure, the film prepared at 200 ◦C is close to the amorphous phase due to the absence of a strong In2O3 diffraction peak. The (2 2 2) diffraction peak of