Indium oxide thin-film homo-junctions: Morphology and electrical properties

Abstract

Indium oxide shows an unusual combination of electrical and optical properties that give rise to a broad range of applications in optoelectronic devices. Here, we report results of structural, x-ray photoelectron spectroscopy, and electrical transport studies of transparent homo-junctions, obtained by sequential growth of polycrystalline thin layers of indium oxide under O2-rich and O2-poor conditions. We find that the growth temperature, which affects significantly film morphology, is critical for the rectifying behavior of the junctions. Only junctions grown at about 350 °C are rectifying. We also find that p-type-like layers have higher concentration of inter-grain oxygen than n-type layers, presumably coming from oxygen-rich deposition conditions and from much larger number of grain boundaries than in n-type layers. We conjecture that the segregation of oxygen ions at grain boundaries is responsible for the formation of inversion layers in O2-rich films and their apparent p-type dc conduction. This mechanism significantly modifies the capacitance-voltage characteristics of the junctions. However, the rectifying mechanism can be accounted for by a space-charge layer at the p-n interface. Such behavior might be important in other polycrystalline thin films with a large number of interface defects at grain boundaries. © 2013 AIP Publishing LLC.