- Email: [email protected]
(La,Ce)2CuO4 trilayer p–i–n junctions
Physica C 460–462 (2007) 1373–1374 www.elsevier.com/locate/physc
Rectification in (La,Sr)MnO3/(Ba,Sr)TiO3/(La,Ce)2CuO4 trilayer p–i–n junctions L.X. Cao *, J. Yuan, H. Wu, B. Xu, B.R. Zhao State Key Laboratory for Superconductivity, Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China Available online 11 April 2007
Abstract Oxide trilayer p–i–n junctions, with p-type La0.67Sr0.33MnO3 (LSMO) manganite layer and n-type La1.89Ce0.11CuO4 (LCCO) cuperate layer separated by Ba0.7Sr0.3TiO3 (BST) titanite insulator layer, have been deposited in situ and characterized. With the increment of the insulator layer thickness, the I–V characteristic of such p–i–n junctions changes from symmetric to asymmetric, and then to symmetric again, given the highest rectifying performance at the BST layer of about 25 nm thick. The largest asymmetry, defined as the ratio of dI/ dV at +2 V and 2 V, respectively, is found >1000. The insulator layer thickness dependency indicates that the transport properties of the p–i–n junctions are dominated by the interplay between the interior fields at the LSMO/BST and BST/LCCO interfaces. Ó 2007 Elsevier B.V. All rights reserved. PACS: 74.78.Db; 73.40.Ei; 79.60.Jv Keywords: Rectification; Electron-doped cuperates; Heterostructures
Electron-doped (n-type) cuperate superconductors differ from their hole-doped counterparts on some ways and therefore are important in studying the high Tc superconductivity. However, they are difficult to be synthesized due to their unique structural features, e.g., absence of apical oxygens. Most experimental studies were performed on L2 xCexCuO4 (L = Pr, Nd, etc.) [1]. As for La2 xCexCuO4, the one with non-magnetic rare earth cation and the one with the highest Tc in all known n-type cuperate, thin films are the only available materials since single-phase bulk materials, let alone single crystals, are very difficult to be obtained [2–4]. Meanwhile, the availability of n-type cuperate superconductor thin films paves a way to study other exotic structures and properties, including oxide p– n junctions [5,6]. In this paper, we present the study on in situ trilayer deposition of La0.67Sr0.33MnO3/Ba0.7Sr0.3TiO3/La1.89-
*
Corresponding author. Tel./fax: +86 10 8264 8117. E-mail address: [email protected] (L.X. Cao).
0921-4534/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2007.04.025
Ce0.11CuO4 (LSMO/BST/LCCO) p–i–n junctions by laser molecular beam epitaxy (LMBE) and also the electrical transport properties of such trilayers. Insulator BST layer is found to play a key role in the rectification of oxide p–i–n junctions. The trilayer system was deposited subsequently one on each other on SrTiO3(0 0 1) substrate. Hole-doped (p-type) colossal magnetoresistance (CMR) manganite La0.67Sr0.33MnO3 (LSMO) film of 150 nm thick was deposited first and served as the bottom layer, while n-type cuperate La1.89Ce0.11CuO4 (LCCO) films of 150 nm thick was deposited last as the top layer, with Ba0.7Sr0.3TiO3 (BST) titanite film of 5–200 nm (5, 10, 15, 20, 25, 30, 40, 50, 100, 150, 200 nm) thick deposited in between the bottom and top layers serving as insulating layer. Detailed deposition procedures will be reported elsewhere. Half of the top LCCO layer and insulator BST layer were etched away and the silver electrodes were deposited onto the thus exposed bottom LSMO and also the top LCCO layers, respectively. Current perpendicular to plane (CPP) measurements were performed at different temperatures
1374
L.X. Cao et al. / Physica C 460–462 (2007) 1373–1374
between 5 K and 300 K for all samples with BST layer of 5–200 nm. LCCO layers of all samples studied are superconducting, with zero transition temperature higher than 22 K (not shown here). One of the X-ray diffraction patterns of the p–i–n junction samples is reproduced in Fig. 1, which reveals single-phased, epitaxial growth. Cross-sectional transmission electron microscopy (not shown here) reveals good crystallinity and clear and sharp interfaces of LCCO/ BST, BST/LSMO, and LSMO/SrTiO3. Current–voltage (I–V) curves for a trilayer with 25 nm thick BST layer at 5 K and 40 K are plotted, as given in Fig. 2. The I–V curves are symmetric for samples with BST layers less than 10 nm or greater than 100 nm thick, asymmetric for samples with BST layer thicknesses in between 10 and 100 nm. The asymmetry ratio AR, i.e., rectification, is defined as the ratio of dI/dV at +2 V and 2 V. In Fig. 3, we plot the
Fig. 1. X-ray diffraction spectrum of LSMO/BST/LCCO trilayer on SrTiO3(0 0 1), showing single-phased, epitaxial growth.
Fig. 3. BST layer thickness dependency of asymmetry ratios AR and junction resistances R for trilayer junctions.
BST layer thickness dependency of asymmetry ratio AR and junction resistance R, which is in fact the dI/dV at 2 V. It is clear that for the thinner BST layer samples, the transport is mainly dominated by tunneling, given the lowest junction resistance R and 1 the asymmetry ratio AR, while for the thicker BST layer samples, dominated by bulk insulating properties, given the much higher junction resistance R and close to 1 the asymmetry ratio AR. This is clearly indicated by the smallest R and the much smaller AR for 5–10 nm BST samples as well as the highest R and smaller AR for 100 nm BST sample, as shown in Fig. 3. For samples with intermediate BST layer thickness, as can be seen in Fig. 3, the asymmetry ratio AR reaches maximum, greater than 1000 for a 25 nm thick BST sample. The phenomena shown here clearly indicate that the rectification properties are mainly dominated by the interplay between the interior fields at the LCCO/BST and BST/LSMO interfaces. Further detailed electrical studies and also the transport properties of such p–i–n junctions under magnetic and optic fields will be published elsewhere. Acknowledgements L.X.C. is supported by the CAS BRJH. This work is supported by the NSF and State Key Program for Basic Research of China. References
Fig. 2. Current perpendicular to plane I–V curves measured at 5 K and 40 K for a trilayer sample with 25 nm thick BST layer, indicating >1000 rectification.
[1] Y. Tokura, H. Takagi, S. Uchida, Nature 337 (1989) 345. [2] M. Naito, M. Hepp, Jpn. J. Appl. Phys. II 39 (2000) L485. [3] A. Sawa, M. Kawasaki, H. Takagi, Y. Tokura, Phys. Rev. B 66 (2002) 014531. [4] H. Wu, L. Zhao, J. Yuan, L.X. Cao, J.P. Zhong, L.J. Gao, B. Xu, P.C. Dai, B.Y. Zhu, X.G. Qiu, B.R. Zhao, Phys. Rev. B 73 (2006) 104512. [5] C. Mitra, P. Raychaudhuri, G. Ko¨bernik, K. Do¨rr, K.-H. Mu¨ller, L. Schultz, R. Pinto, Appl. Phys. Lett. 79 (2001) 2408. [6] H. Tanaka, J. Zhang, T. Kawai, Phys. Rev. Lett. 88 (2002) 027204.
Rectification in (La,Sr)MnO3/(Ba,Sr)TiO3/(La,Ce)2CuO4 trilayer p–i–n junctions L.X. Cao *, J. Yuan, H. Wu, B. Xu, B.R. Zhao State Key Laboratory for Superconductivity, Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China Available online 11 April 2007
Abstract Oxide trilayer p–i–n junctions, with p-type La0.67Sr0.33MnO3 (LSMO) manganite layer and n-type La1.89Ce0.11CuO4 (LCCO) cuperate layer separated by Ba0.7Sr0.3TiO3 (BST) titanite insulator layer, have been deposited in situ and characterized. With the increment of the insulator layer thickness, the I–V characteristic of such p–i–n junctions changes from symmetric to asymmetric, and then to symmetric again, given the highest rectifying performance at the BST layer of about 25 nm thick. The largest asymmetry, defined as the ratio of dI/ dV at +2 V and 2 V, respectively, is found >1000. The insulator layer thickness dependency indicates that the transport properties of the p–i–n junctions are dominated by the interplay between the interior fields at the LSMO/BST and BST/LCCO interfaces. Ó 2007 Elsevier B.V. All rights reserved. PACS: 74.78.Db; 73.40.Ei; 79.60.Jv Keywords: Rectification; Electron-doped cuperates; Heterostructures
Electron-doped (n-type) cuperate superconductors differ from their hole-doped counterparts on some ways and therefore are important in studying the high Tc superconductivity. However, they are difficult to be synthesized due to their unique structural features, e.g., absence of apical oxygens. Most experimental studies were performed on L2 xCexCuO4 (L = Pr, Nd, etc.) [1]. As for La2 xCexCuO4, the one with non-magnetic rare earth cation and the one with the highest Tc in all known n-type cuperate, thin films are the only available materials since single-phase bulk materials, let alone single crystals, are very difficult to be obtained [2–4]. Meanwhile, the availability of n-type cuperate superconductor thin films paves a way to study other exotic structures and properties, including oxide p– n junctions [5,6]. In this paper, we present the study on in situ trilayer deposition of La0.67Sr0.33MnO3/Ba0.7Sr0.3TiO3/La1.89-
*
Corresponding author. Tel./fax: +86 10 8264 8117. E-mail address: [email protected] (L.X. Cao).
0921-4534/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2007.04.025
Ce0.11CuO4 (LSMO/BST/LCCO) p–i–n junctions by laser molecular beam epitaxy (LMBE) and also the electrical transport properties of such trilayers. Insulator BST layer is found to play a key role in the rectification of oxide p–i–n junctions. The trilayer system was deposited subsequently one on each other on SrTiO3(0 0 1) substrate. Hole-doped (p-type) colossal magnetoresistance (CMR) manganite La0.67Sr0.33MnO3 (LSMO) film of 150 nm thick was deposited first and served as the bottom layer, while n-type cuperate La1.89Ce0.11CuO4 (LCCO) films of 150 nm thick was deposited last as the top layer, with Ba0.7Sr0.3TiO3 (BST) titanite film of 5–200 nm (5, 10, 15, 20, 25, 30, 40, 50, 100, 150, 200 nm) thick deposited in between the bottom and top layers serving as insulating layer. Detailed deposition procedures will be reported elsewhere. Half of the top LCCO layer and insulator BST layer were etched away and the silver electrodes were deposited onto the thus exposed bottom LSMO and also the top LCCO layers, respectively. Current perpendicular to plane (CPP) measurements were performed at different temperatures
1374
L.X. Cao et al. / Physica C 460–462 (2007) 1373–1374
between 5 K and 300 K for all samples with BST layer of 5–200 nm. LCCO layers of all samples studied are superconducting, with zero transition temperature higher than 22 K (not shown here). One of the X-ray diffraction patterns of the p–i–n junction samples is reproduced in Fig. 1, which reveals single-phased, epitaxial growth. Cross-sectional transmission electron microscopy (not shown here) reveals good crystallinity and clear and sharp interfaces of LCCO/ BST, BST/LSMO, and LSMO/SrTiO3. Current–voltage (I–V) curves for a trilayer with 25 nm thick BST layer at 5 K and 40 K are plotted, as given in Fig. 2. The I–V curves are symmetric for samples with BST layers less than 10 nm or greater than 100 nm thick, asymmetric for samples with BST layer thicknesses in between 10 and 100 nm. The asymmetry ratio AR, i.e., rectification, is defined as the ratio of dI/dV at +2 V and 2 V. In Fig. 3, we plot the
Fig. 1. X-ray diffraction spectrum of LSMO/BST/LCCO trilayer on SrTiO3(0 0 1), showing single-phased, epitaxial growth.
Fig. 3. BST layer thickness dependency of asymmetry ratios AR and junction resistances R for trilayer junctions.
BST layer thickness dependency of asymmetry ratio AR and junction resistance R, which is in fact the dI/dV at 2 V. It is clear that for the thinner BST layer samples, the transport is mainly dominated by tunneling, given the lowest junction resistance R and 1 the asymmetry ratio AR, while for the thicker BST layer samples, dominated by bulk insulating properties, given the much higher junction resistance R and close to 1 the asymmetry ratio AR. This is clearly indicated by the smallest R and the much smaller AR for 5–10 nm BST samples as well as the highest R and smaller AR for 100 nm BST sample, as shown in Fig. 3. For samples with intermediate BST layer thickness, as can be seen in Fig. 3, the asymmetry ratio AR reaches maximum, greater than 1000 for a 25 nm thick BST sample. The phenomena shown here clearly indicate that the rectification properties are mainly dominated by the interplay between the interior fields at the LCCO/BST and BST/LSMO interfaces. Further detailed electrical studies and also the transport properties of such p–i–n junctions under magnetic and optic fields will be published elsewhere. Acknowledgements L.X.C. is supported by the CAS BRJH. This work is supported by the NSF and State Key Program for Basic Research of China. References
Fig. 2. Current perpendicular to plane I–V curves measured at 5 K and 40 K for a trilayer sample with 25 nm thick BST layer, indicating >1000 rectification.
[1] Y. Tokura, H. Takagi, S. Uchida, Nature 337 (1989) 345. [2] M. Naito, M. Hepp, Jpn. J. Appl. Phys. II 39 (2000) L485. [3] A. Sawa, M. Kawasaki, H. Takagi, Y. Tokura, Phys. Rev. B 66 (2002) 014531. [4] H. Wu, L. Zhao, J. Yuan, L.X. Cao, J.P. Zhong, L.J. Gao, B. Xu, P.C. Dai, B.Y. Zhu, X.G. Qiu, B.R. Zhao, Phys. Rev. B 73 (2006) 104512. [5] C. Mitra, P. Raychaudhuri, G. Ko¨bernik, K. Do¨rr, K.-H. Mu¨ller, L. Schultz, R. Pinto, Appl. Phys. Lett. 79 (2001) 2408. [6] H. Tanaka, J. Zhang, T. Kawai, Phys. Rev. Lett. 88 (2002) 027204.