IEEE TRANSACTIONS ON DEVICE AND MATERIALS RELIABILITY, VOL. 12, NO. 1, MARCH 2012 133 Degradation Processes in Surface Layers of Indium Oxide David L. Fuks, Arnold E. Kiv, Dina V. Shapiro, Vyacheslav V. Golovanov, Vasilij N. Šmatko, and Ivan I. Donchev Abstract—The degradation of In 2 O 3 (110) surface as a working surface in the In 2 O 3 -based sensor is studied. Theoretical and experimental investigations of electronic and atomic processes on this surface caused by the adsorption of H 2 molecules are performed. In the framework of the density functional theory, we determined the energetically preferable position of the adsorbed H 2 molecule over In 2 O 3 surface. It was found that the adsorbed H 2 molecule is mainly “bonded” with In atom. The redistribution of the electron density around In atom leads to a weakening of chemical bonds in the vicinity of In atom, and this circumstance is a reason of its destabilization. The temperature dependence of the resistance of In 2 O 3 films in a wide interval of temperatures was measured. This dependence is characterized by a specific max- imum. The obtained experimental results are interpreted using theoretical results concerning a destabilization of surface In atoms induced by the adsorbed H 2 molecules and, on the basis of our recent results in an earlier paper, concerning a high-temperature degradation of the In 2 O 3 (110) surface layers as a working surface in sensor devices. We suggested a two-stage model of the degrada- tion process: In the first stage, the disordering of surface caused by H 2 -adsorption-stimulated displacement of In atoms leads to the increase of surface resistance, and in the second stage, displaced In atoms form precipitates and this process causes a metallization of In 2 O 3 surface and a decrease of the resistance. Index Terms—Degradation, density functional theory (DFT), semiconductor films, sensor systems. I. I NTRODUCTION I NDIUM OXIDE (In 2 O 3 ) is the n-type wide band gap mater- ial having wide applications in the modern electronics (pho- toelectric devices, heat-reflecting mirrors, high transparency layers, gas sensor devices and others). Due to this reason, thin films, nanoparticles and nanowires of In 2 O 3 are intensively studied during last decade. In 2 O 3 -based sensors exhibit high sensitivity and fast response to different gases (in particular to CO and CH 4 ) and low interference to air humidity, [1]. To reach a high sensitivity of In 2 O 3 film it should be heated (the working temperature of sensor device is 350–400 ◦ C). Practically in the one-electrode device this heating is caused by current that passes the Pt electrode, the substrate and the film. Manuscript received September 18, 2010; accepted November 13, 2011. Date of publication December 6, 2011; date of current version March 7, 2012. This work was supported by the Binational Science Foundation under Grant 2006056. D. L. Fuks, A. E. Kiv, and D. V. Shapiro are with the Department of Materials Engineering, Ben-Gurion University of the Negev, Beer Sheva 84105, Israel (e-mail: fuks@bgu.ac.il; kiv@bgu.ac.il; sh.dinu6@gmail.com). V. V. Golovanov and I. I. Donchev are with the Department of Physical and Mathematical Modelling, South-Ukrainian National Pedagogical University, 65008 Odessa, Ukraine (e-mail: alban@te.net.ua; donchev@pdpu.edu.ua). V. N. Šmatko is with the Institute of Electrical Engineering, Slovak Academy of Sciences, 845111 Bratislava, Slovak Republic (e-mail: eleksmat@savba.sk). Digital Object Identifier 10.1109/TDMR.2011.2178244 Authors of [2] studied the electrical conductivity mechanism as a function of the temperature in In 2 O 3 films with various thicknesses. It was found that the temperature dependence of the electrical conductivity is substantially different for ul- trathin (< 1500 Å) and thin films (> 1500 Å). In [3] the size-dependent structural properties of In 2 O 3 nanoparticles are described. The peaks in the XRD spectrum were found for cubic In 2 O 3 phase that correspond to the planes: (222)—the largest peak, than (400) and (440)—two approximately equal smaller peaks and (622)—the smallest peak. The results of investigations of InO x thin films are presented in [4]. De- position of nanocrystalline films was performed by dc mag- netron sputtering, [5], [6]. XRD studies have confirmed the preferential growth orientation along the (222) direction and a corresponding improvement in crystallinity with increasing deposition temperature. The single-crystalline In 2 O 3 nanowires synthesized by a laser ablation method and characterized using various techniques are described in [7]. A precise control over the nanowire diameter down to 10 nm was achieved by using monodispersed gold clusters as the catalytic nanoparticles. XRD patterns of such nanowire samples were used to examine the crystal structure of nanowires. All samples showed similar XRD patterns, indicating the high crystallinity of nanowires. There are four major diffraction peaks. They can be indexed to the (222), (400), (440), and (622) crystal planes of a cubic structure of bulk In 2 O 3 with a cell constant a = 1.01 nm. Nanowires with diameters less than 30 nm were used to make nanowire-based field effect transistors. The surface structure of In 2 O 3 films have been studied by authors of [8]. They are employed theoretical modeling for geometries, electronic structures and surface energetics to- gether with experimental methods for surface characterization. It was found that the most abundant (400) surface reconstructs considerably leading to formation of surface mono-oxygen and di-oxygen forms. This uppermost surface layer exhibits a high ability to reduction/oxidation processes during the thermal treatment. The unsaturated indium ions appearing at the recon- structed surface serve as the active sites for the chemisorbed oxygen species. Therefore, according to results obtained in this work, the mechanisms of In 2 O 3 sensitivity to reducing gases include both “redox” and catalytic effects in a very thin surface layer. In [9] the electronic structure of In 2 O 3 polymorphs is calcu- lated from first principles using DFT and many-body perturba- tion theory. The results for gaps, d-band positions, and density of states (DOS) are shown in agreement with available experimen- tal data. In [10] the results of DFT calculations of the electronic structure of a clean (110) surface and a bulk of In 2 O 3 crystal 1530-4388/$26.00 © 2011 IEEE