Epitaxial growth and rectification characteristics of double perovskite oxide La 2 NiMnO 6 films on Nb-SrTiO 3 single crystal substrates G.Y. Gao a , Y. Wang a , Y. Jiang a , L.F. Fei a , N.Y. Chan a , H.L.W. Chan a, ⁎, W.B. Wu b a Department of Applied Physics and Materials Research Center, The Hong Kong Polytechnic University, Hong Kong SAR, China b Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei 230026, China abstract article info Article history: Received 29 April 2010 Received in revised form 27 March 2011 Accepted 31 March 2011 Available online 7 April 2011 Keywords: Thin films Double perovskite Pulsed laser deposition Epitaxial growth pn junctions Rectifying behavior High-quality thin films of double perovskite La 2 NiMnO 6 (LNMO) were epitaxially grown on Nb-doped SrTiO 3 (NSTO) substrates by pulsed laser deposition. The films were found to undergo a ferromagnetic-to-paramagnetic transition at ~280 K, which is consistent with the literature report. In the electrical measurements, typical rectifying behavior was observed in the LNMO/NSTO heterojunction. The diffusion voltage (V D ) increases linearly with temperature (T) during cooling until T = 170 K. At T b 170 K, V D increases at a higher rate and the V D –T relationship becomes non-linear. A disordered phase related spin polarization was used to understand such behaviors in the heterojunctions. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Lately double perovskite oxides have attracted much interest because of their interesting physical properties being half-metallic, ferromagnetic, dielectric, and semiconducting behaviors [1–4]. As a ferromagnetic semiconductor, La 2 NiMnO 6 (LNMO) belongs to a family of A 2 B′B″O 6 double perovskite oxides, where A is an alkaline-earth or rare-earth ion, and B′ and B″ are transition-metal ions. In this type of compound, B′O 6 and B″O 6 octahedra are orderly in rock salt configu- ration in pseudocubic structure. Many studies have focused on the magnetic properties, electronic structure of bulk double perovskite to better understand the magnetic interactions and cations valence states in the oxides [5,6]. For example, it is found that LNMO undergoes a ferromagnetic–paramagnetic transition at ~280 K, and the magnetic behaviors can be well described by Kanamori–Goodenough rules, but there are disagreements about the B-site cations both oxidation state (i.e.Ni 3+ /Mn 3+ or Ni 2+ /Mn 4+ ) and the Ni/Mn ordering. More recently, there is increasing interest on the deposition and characterization of LNMO thin films [7–10]. It is worth to note that the energy gap (E g ) for LNMO film is ~1.5 eV (based on the x-ray absorption spectra data), while the energy gap of n-type SrTiO 3 : 0.7 wt.% Nb (NSTO) semiconductor is 3.2 eV [11,12]. It is thus expected that the LNMO/NSTO heterostructure could form an all-oxide pn junction which potentially can be used for constructing Si-technology compatible electronic devices, just as those simple perovskite thin film based heterostructures [13,14]. As we have noticed, however, there is rather limited work on such heterostructures. 2. Experimental details The La 2 NiMnO 6 (LNMO) films (~ 110 nm thick) were grown on (001) oriented 0.7% Nb-doped SrTiO 3 (NSTO) single crystal substrates from a rotating LNMO target by pulsed laser deposition with a KrF excimer laser (Lambda Physik, wave length = 248 nm). A ceramic target of the stoichiometric LNMO was synthesized by the conven- tional solid state reaction method using high purity powdered La 2 O 3 (99.99%), NiO (99.9%), and MnO 2 (99.9+%) [4]. The distance between substrate and target was about 5 cm. The energy of the laser beam was about 300 mJ and the pulse repetition rate was 5 Hz. During the deposition, the oxygen pressure and temperature during deposition were kept at 100 Pa and 750 °C respectively and the film growth rate was found to be ~7 nm/min. After deposition, the chamber was filled to 1 atm with high purity oxygen and then the sample was cooled down to room temperature. The crystal structure of the as-deposited film was examined by x-ray diffraction (XRD) with Cu Kα radiation and a Ni filter (Bruker AXS D8 Discover). The microstructure of LNMO/NSTO heterojunction was characterized by high-resolution transmission electron microscopy (HRTEM, JEOL 2010 electron microscope equipped with energy dispersive x-ray, operating at voltage of 200 kV). The cross-sectional specimens for TEM have been prepared using standard procedures involving the sequence of mechanical grinding, polishing, dimpling and Thin Solid Films 519 (2011) 6148–6150 ⁎ Corresponding author. Tel.: + 852 2766 5692; fax: + 852 2766 1202. E-mail address: apahlcha@inet.polyu.edu.hk (H.L.W. Chan). 0040-6090/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2011.03.137 Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf