www.afm-journal.de FULL PAPER © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1 www.MaterialsViews.com wileyonlinelibrary.com Tae Heon Kim, Byung Chul Jeon, Taeyoon Min, Sang Mo Yang, Daesu Lee, Yong Su Kim, Seung-Hyub Baek, Wittawat Saenrang, Chang-Beom Eom, Tae Kwon Song, Jong-Gul Yoon,* and Tae Won Noh 1. Introduction The functional properties of ferroelectric materials have attracted much attention for their potential application in microelectronic devices, such as ferroelectric nonvolatile memo- ries. [1–9] Recently, polarization control of charge transport in fer- roelectrics has been extended to novel nanoelectronic devices, which include ferroelectric resistive switching memories, [10–14] ferroelectric/multiferroic tunnel junctions, [15–20] and domain wall nanoelectronics. [21–25] The modulation of interfacial poten- tials by electric polarization has been suggested as the origin of ferroelectric resistive switching and switchable diode effects [6,8,26,27] that enable non-destructive readout for high-density memory applications. It has been reported that the potential profiles of the Schottky barriers for carrier injection could be selec- tively changed by polarization reversal. [6] This indicates that polarization charges accumulated at the interface could con- trol the Schottky-like metal/ferroelectric interfacial barrier. The use of ferroelectric domains for continuous control of the charge transport in ferroelectric films is of further interest, because domain configu- ration affects polarization charge at the metal/ferroelectric interface. Such domain engineering for the control of charge transport has not been explored yet. The robust ferroelectricity [28] and small band gap [4] of BiFeO 3 (BFO) are quite attractive for examining the influence of ferroelectric polarization on charge transport. At room temperature (RT), the remnant polarization ( P r ) is almost 100 μC cm -2 along the [111] direction in pseudocubic notation. [28] In addition, the band gap of BFO ( ≈2.2 to 2.6 eV) is narrow compared with that of typical ferro- electric materials such as Pb(Zr,Ti)O 3 and BaTiO 3 . [4] Due to this narrow band gap, the Schottky barrier height at a metal/BFO contact can be relatively small. The large polarization charge can easily modulate interfacial barrier. These electronic charac- teristics make BFO as a prototype oxide semiconductor system with intriguing functionalities, such as ferroelectric resistive switching [10,12,13] and switchable photovoltaics. [4,6,9,10,27] Recently, it has been reported that the performance of resistive switching Continuous Control of Charge Transport in Bi-Deficient BiFeO 3 Films Through Local Ferroelectric Switching It is demonstrated that electric transport in Bi-deficient Bi 1-δ FeO 3 ferroelec- tric thin films, which act as a p-type semiconductor, can be continuously and reversibly controlled by manipulating ferroelectric domains. Ferroelectric domain configuration is modified by applying a weak voltage stress to Pt/ Bi 1-δ FeO 3 /SrRuO 3 thin-film capacitors. This results in diode behavior in macroscopic charge-transport properties as well as shrinkage of polariza- tion-voltage hysteresis loops. The forward current density depends on the voltage stress time controlling the domain configuration in the Bi 1-δ FeO 3 film. Piezoresponse force microscopy shows that the density of head-to- head/tail-to-tail unpenetrating local domains created by the voltage stress is directly related to the continuous modification of the charge transport and the diode effect. The control of charge transport is discussed in conjunc- tion with polarization-dependent interfacial barriers and charge trapping at the non-neutral domain walls of unpenetrating tail-to-tail domains. Because domain walls in Bi 1- δ FeO 3 act as local conducting paths for charge transport, the domain-wall-mediated charge transport can be extended to ferroelectric resistive nonvolatile memories and nanochannel field-effect transistors with high performances conceptually. DOI: 10.1002/adfm.201201490 Dr. T. H. Kim, B. C. Jeon, T. Min, S. M. Yang, Dr. D. Lee, Dr. Y. S. Kim, Prof. T. W. Noh ReCFI, Department of Physics and Astronomy Seoul National University Seoul 151-747, Korea Dr. S.-H. Baek, W. Saenrang, Prof. C.-B. Eom Department of Materials Science and Engineering University of Wisconsin Madison, WI 53706, USA Prof. T. K. Song School of Nano and Advanced Materials Engineering Changwon National University Changwon, Gyengnam 641-773, Korea Prof. J.-G. Yoon Department of Physics University of Suwon Hwaseong, Gyeonggi-do 445-743, Korea E-mail: jgyoon@suwon.ac.kr Adv. Funct. Mater. 2012, DOI: 10.1002/adfm.201201490