Pulsed-laser growth of In2O3 thin films on YSZ(111) substrates

Abstract

Indium(III) oxide (In2O3) is a wide bandgap semiconductor and belongs to the class of transparent conductive oxides, which combine high electrical conductivity and optical transparency in the visible region. Achieving a better understanding of the atomicscale surface characteristics by investigating well-defined single-crystal model systems is of paramount importance to optimize the functionality of In2O3-based technology. Undoped In2O3 single crystals are not commercially available, and synthetically grown ones are usually very small, limiting the investigation by area-averaging techniques such as temperature programmed desorption and X-ray photoelectron spectroscopy (XPS). To compensate for the lack of large In2O3 single crystals, we have prepared well-ordered and atomically-flat In2O3(111) thin films, with a thickness of few hundreds of nanometres. The films were grown on Y-stabilized zirconia (111) substrates by pulsed laser deposition (PLD). Their structure, chemical composition, and morphology were characterized by electron (RHEED, LEED) and x-ray diffraction (XRD), XPS, atomic-force microscopy (AFM), and scanning tunneling microscopy (STM). By optimizing the growth parameters (temperature and oxygen background pressure) and investigating their effect on the film morphology and structure, we could obtain In2O3(111) films exhibiting properties comparable to the best single crystalline samples available. According to AFM measurements after growth, such films exhibit atomically-flat terraces with an average terrace width of ∼ 150 nm, which increases the typical terrace width of an In2O3 single crystal by a factor of 3−4. XRD reveals that the In2O3 film adopts the cubic bixbyite structure. The out-of-plane lattice parameter, as well as the typical peak widths, are comparable to those of single-crystalline samples, indicating high crystalline quality. STM investigations show a very good agreement with the STM results of In2O3 single crystals, both on the small and on the large scale. The similarity in high resolution STM measurements strongly promotes the use of the grown films as an equivalent replacement of In2O3(111) single crystals for different experimental setups.