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Properties of La0.75Sr0.25MnO3 films grown on Si substrate with Si1−xGex and Si1−yCy buffer layers
Thin Solid Films 515 (2006) 411 – 415 www.elsevier.com/locate/tsf
Properties of La0.75Sr0.25MnO3 films grown on Si substrate with Si1 x Gex and Si1 y Cy buffer layers Joo-Hyung Kim *, Alexander M. Grishin, Henry H. Radamson Department of Microelectronics and Information Technology, Royal Institute of Technology, SE-164 40 Stockholm-Kista, Sweden Available online 27 January 2006
Abstract The structural and electrical properties of La0.75Sr0.25MnO3 (LSMO) film on Bi4Ti3O12 (BTO)/CeO2/YSZ buffered Si1 x Gex /Si (0.05 x 0.2 for compressive strain), blank Si, and Si1 y Cy /Si ( y = 0.01 for tensile) were studied. X-ray high resolution reciprocal lattice mapping (HRRLM) and atomic force microscopy (AFM) show that structural properties of LSMO and buffer oxide layers are strongly related to the strain induced by amount of Ge and C contents. The RMS roughness of LSMO on Si1 x Gex /Si has a tendency to increase with increasing of Ge content. Electrical properties of LSMO film with Ge content up to 10% are slightly improved compared to blank Si whereas higher resistivity values were obtained for the samples with higher Ge content. D 2006 Elsevier B.V. All rights reserved. PACS: 73.50.-h Electronic transport phenomena in thin films Keywords: Manganites; Heteroepitaxial film structure on Si; Strain effect; High resolution reciprocal lattice mapping (HRRLM); Temperature coefficient of resistance (TCR)
1. Introduction High quality complex oxide films find various applications for electronic and photonic devices. Mixed-valence perovskite manganese oxides, La1 x A x MnO3 (A is Ba, Ca, Sr and Pb, 0.20 < x < 0.50) exhibit effects of colossal magnetoresistivity (CMR) and high-value temperature coefficient of resistance (TCR = 1 / RIdR / dT) due to metal (ferromagnetic phase) to insulator (paramagnetic) phase transition nearby Curie temperature, Tc. The mechanism of this phenomenon was early explained by the double-exchange interaction that the transfer of eg electron in 3d shell occurs between Mn4+ and Mn3+ ions [1]. Spin dependent metal-insulator transition in CMR materials was intensively reviewed in experiments and theoretical studies [2– 4]. Unusual electrical/magnetic properties of CMR manganites have been also considered for ferroelectric field effect transistor (FeFET), nonvolatile magnetic random access memory (MRAM) and infrared (IR) bolometric devices [5– 7]. To grow high quality CMR manganites, three relative material properties of CMR film and substrate were found to * Corresponding author. Tel.: +46 8 790 4185; fax: +46 8 752 7850. E-mail address: [email protected] (J.-H. Kim). 0040-6090/$ - see front matter D 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2005.12.222
be an important issue: lattice mismatch, different thermal expansion and chemical reaction. Lattice mismatch causes bior uniaxial strain that affects structural, electrical and magnetic properties of thin CMR films [8]. Therefore, to obtain high performance CMR manganite films one should control the strain induced from substrate. To minimize the lattice mismatch, CMR manganites were grown on oxide substrates, ˚ ) and SrTiO3 (a = 3.91 A ˚ ). Depending on as LaAlO3 (a = 3.80 A the strain, compressive in LaAlO3 or tensile in SrTiO3, different magnetic domains, feather-like or maze-like, respectively, have been observed [9]. Moreover, the electrical properties of La0.75Sr0.25MnO3 film strongly depend on film’s thickness and the type of oxide substrate [10]. Comprehensive theory of the misfit strain developed for the perovskite heteroepitaxial thin films appears to be in a good agreement with the X-ray determined out-of-plane lattice parameter c [11]. Difference in the thermal expansion coefficients of oxide films and substrate results in structural phase transformations and appearance of poly-twin domains during cooling down from the growth temperature [12]. To introduce CMR manganites to the matured semiconductor technology, the large lattice mismatch between CMR ˚ ) and semiconductor substrate manganite (a = 3.8 – 3.9 A ˚ (a = 5.431 and 5.653 A for Si and GaAs) must be overcome.
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tune the additional strain from tensile regime (Si1 y Cy ) to compressive regime (Si1 x Gex ) layers [14]. Fig. 1 presents the schematic of growth mechanism of Si1 y Cy and Si1 x Gex layers on Si substrates. Due to smaller lattice parameter of Si1 y Cy in Fig. 1(a) and lager lattice of Si1 x Gex than Si crystal in Fig. 1(b), the Si1 y Cy and Si1 x Gex layers on Si are under in-plane tensile and compressive strain, respectively. Therefore, using extra strained layers prior to CMR manganite film processing, the Si1 x Gex and Si1 y Cy may affect the stability of CMR film and BTO/CeO2/YSZ buffer layers. Here, we investigate the strain effect of Si1 x Gex (for extra compressive) and Si1 y Cy (for tensile) layers on structural and electrical properties of La0.75Sr0.25MnO3 (LSMO) films grown under the same optimized deposition conditions on BTO/CeO2/YSZ buffered Si substrates. 2. Experimental details
Fig. 1. Schematic of (a) Si1 y Cy and (b) Si1 x Gex layers on Si substrates.
YSZ and CeO2/YSZ are commonly used for buffer layers on Si substrate. In our previous report, high quality epitaxial La0.67(Sr,Ca)0.33MnO3 films on Si substrates with Bi4Ti3O12(BTO)/CeO2/YSZ buffer layers were successfully grown for bolometric applications [13]. But until now, there are very few reports for systematic studies of strain effect between CMR films and Si substrate. For this purpose, Si1 x Gex and Si1 y Cy layers can be directly applied on Si substrate with an appropriate Ge and C amount to
Si1 x Gex (x = 0.05 –0.20) and Si1 y Cy ( y = 0.01) films were grown on Si (100) substrates at 650 and 575 -C correspondingly, by reduced pressure chemical vapor deposition (RPCVD, Epsilon 2000) technique using the N2 purged loadlock to minimize O2 contamination. To create Si1 x Gex layers on Si substrate, silane (SiH4) and germane (GeH4) were supplied for silicon and germanium precursors with H2 carrier gas. For Si1 y Cy layer, silane and methyl-silane (SiH3CH3) were added. Because epitaxial film growth is very sensitive to surface condition of substrate, all of Si wafer were chemically cleaned before loading into RPCVD chamber. The Ge content and thickness of Si1 x Gex and Si1 y Cy layers were calculated from the high-resolution X-ray diffraction (HRXRD) patterns. The deposited Si1 x Gex and Si0.99C0.01 layer thicknesses were ˚ . After deposition of BTO around 1030¨1200 and 1200 A ˚ ˚ ˚ ) buffer layers, 500 A ˚ (1000 A) / CeO2(400 A) / YSZ (300 A thick LSMO films were sintered by KrF pulsed laser deposition (PLD) method at 750 -C, 0.4 Torr of O2 on the Si1 x Gex /Si, Si and Si0.99C0.01/Si substrates. After films’
Fig. 2. Rocking curves around (004) Bragg reflection of as-grown Si1 y Cy /Si and Si1 x Gex /Si. The arrows indicate main peaks of Si1 y Cy /Si and Si1 x Gex /Si layers.
J.-H. Kim et al. / Thin Solid Films 515 (2006) 411 – 415
413
Fig. 3. Reciprocal lattice mappings of heteroepitaxial La0.75Sr0.25MnO3/Bi4Ti3O12/CeO2/YSZ films on (a) Si0.99C0.01/Si, (b) Si, (c) Si0.9Ge0.1/Si, and (d) Si0.8Ge0.2/Si substrates.
growth, in situ post annealing was executed at 730 -C in 500 Torr of O2 for 5 min. More details of deposition conditions can be found elsewhere [13]. The structural quality and surface morphology of all samples were investigated by high resolution reciprocal lattice mapping (HRRLM), HRXRD and atomic force microscopy (AFM, Nanoscope Dimension 3100). Temperature-dependant electrical properties of LSMO
films on different strained substrates were measured by fourprobe technique. 3. Results and discussion Fig. 2 shows rocking curves recorded by HRXRD around Si (004) Bragg reflection of as-grown Si1 x Gex /Si, and Si0.99C0.01/
Fig. 4. Surface morphology of Bi4Ti3O12/CeO2/YSZ buffered La0.75Sr0.25MnO3 films on (a) Si0.99C0.01/Si, (b) Si, (c) Si0.9Ge0.1/Si, and (d) Si0.8Ge0.2/Si.
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Fig. 5. Temperature-dependent resistivity and corresponding temperature coefficient of resistance (TCR) of LSMO films on Si1 x Gex /Si and Si.
Si. Here, LSMO film on Si substrate was considered as a reference sample for the strained Si1 x Gex /Si and Si0.99C0.01/Si structures. From the rocking curves, main peak positions and fringes of all Si1 x Gex and Si0.99C0.01 layers on Si are clearly observed. The estimated lattice parameters of Si0.99C0.01, Si0.95Ge0.05, Si0.9Ge0.1 and Si0.8Ge0.2 layers were 5.395, 5.441, ˚ , respectively. The arrows in Fig. 2 represent 5.451 and 5.472 A main peaks of grown Si1 x Gex and Si0.99C0.01 layers. After deposition of heteroepitaxial LSMO/BTO/CeO2/YSZ structure on strained Si1 x Gex /Si and Si0.99C0.01/Si, the full width half maximum (FWHM) of LSMO-002 Bragg reflection of all samples are 1.10- 0.85-, 0.81- and 1.10- for Si0.99C0.01/ Si, Si, Si0.9Ge0.1/Si and Si0.8Ge0.2/Si, respectively. For detailed investigation of structural relation between the layers, HRRLM around (004) reflection was performed [15]. All of layers including substrate are distinguished by peak position in Fig. 3. In these maps, there is a clear difference in the intensity of the main contours and the shape of BTO-0022 and LSMO-003 peaks between Fig. 3(b) and (d). The shape of BTO-0022 peak changes from ellipsoid in Si0.8Ge0.2 and Si0.99C0.01 samples to a rhombic for Si0.9Ge0.1 and Si samples. There is no change of c lattice parameter observed since no shift in the peak position. Therefore, the changes of the BTO0022 shape stem from alteration between a and b lattice parameters due to biaxial strain change [16]. Fig. 4 shows surface morphology of all PLD-grown LSMO samples recorded in tapping mode AFM measurements. The scan area and rate during measurements were 2 2 Am2 and 1 Hz, respectively. Root mean square (RMS) surface roughness ˚ for Si0.95Ge0.05/Si, of LSMO films was 16.1, 18.0 and 18.6 A Si0.9Ge0.1/Si and Si0.8Ge0.2/Si, respectively. These results indicate that the roughness of LSMO layers on Si1 x Gex /Si has a tendency to increase with increasing of Ge content and is related to extra compressive strain. However, the surface of LSMO film on Si0.99C0.01/Si, under excessive tensile strain, has ˚. the lowest value of RMS roughness, 14.1 A
For electrical measurements, normalized temperature-dependent resistivity is presented in Fig. 5. All curves of LSMO films on Si1 x Gex /Si, except Si0.8Ge0.2/Si, show similar electrical characteristics whereas Si0.99C0.0.1/Si, not shown here, exhibits very large resistivity, q max = 126 kV I cm. There is a slight improvement in TCR value of Si0.9Ge0.1/Si compared to Si. 4. Conclusions Structural and electrical properties of La0.75Sr0.25MnO3 films on Bi4Ti3O12/CeO2/YSZ buffered Si1 x Gex /Si (0.05 x 0.2), Si, and Si0.99C0.01/Si were investigated to understand strain effects. For Si1 x Gex /Si, the shape of reciprocal lattice maps of Bi4Ti3O12(0022) Bragg reflections is strongly related to LSMO film quality, varies from rhombic to elliptic one due to modification of a and b lattice parameters. The RMS roughness of LSMO on Si1 x Gex /Si is dependent on Ge content. LSMO films on Si0.8Ge0.2/Si and Si0.99C0.01/Si show higher resistivity and low TCR values compared to Si sample due to excessive compressive and tensile strain, respectively. References [1] C. Zener, Phys. Rev. 82 (1951) 403. [2] E.O. Wollan, W.C. Koehler, Phys. Rev. 100 (1995) 545. [3] Y. Morimoto, A. Asamitsu, H. Kuwahara, Y. Tokura, Nature 380 (1996) 141. [4] A.J. Millis, B.I. Shraiman, R. Mueller, Phys. Rev. Lett. 77 (1996) 175. [5] T. Venkatesan, M. Rajeswari, Zi-Wen Dong, S.B. Ogale, R. Ramesh, Phil. Trans. R. Soc. Lond., A 356 (1998) 1661. [6] Y. Lu, X.W. Li, G.Q. Gong, G. Xiao, A. Gupta, P. Lecoeur, J.Z. Sun, Y.Y. Wang, V.P. Dravid, Phys. Rev., B 54 (1996) R8357. [7] A. Lisauskas, S.I. Khartsev, A. Grishin, Appl. Phys. Lett. 77 (2000) 756; A. Lisauskas, S.I. Khartsev, A. Grishin, Appl. Phys. Lett. 77 (2000) 3302. [8] Joonghoe Dho, Y.N. Kim, Y.S. Hwang, J.C. Kim, N.H. Hur, Appl. Phys. Lett. 82 (2003) 1434. [9] C. Kwon, M.C. Robson, K.-C. Kim, J.Y. Gu, S.E. Loftland, S.M. Bhaget, Z. Trajanovic¸, M. Rajeswari, T. Venkatesan, A.R. Kratz, R.D. Gomez, R. Ramesh, J. Magn. Magn. Mater. 172 (1997) 229.
J.-H. Kim et al. / Thin Solid Films 515 (2006) 411 – 415 [10] S.I. Khartsev, P. Johnsson, A.M. Grishin, J. Appl. Phys. 87 (2000) 2394. [11] C.L. Canedy, H. Li, S.P. Alpay, L. Salamance-Riba, A.L. Roytburd, R. Ramesh, Appl. Phys. Lett. 77 (2000) 1695. [12] S.P. Alpay, A.L. Roytburd, J. Appl. Phys. 83 (1998) 4714. [13] J.-H. Kim, S.I. Khartsev, A.M. Grishin, Appl. Phys. Lett. 82 (2003) 4295.
415
[14] J.P. Dismukes, L. Ekstrom, R.J. Paff, J. Phys. Chem. 68 (1964) 3021. [15] E. Koppensteiner, G. Bauer, H. Kibbel, E. Kasper, J. Appl. Phys. 76 (1994) 3489. [16] Y. Lin, X. Chen, S.W. Liu, C.L. Chen, Jang-Sik Lee, Y. Lee, Q.X. Jia, A. Bhalla, Appl. Phys. Lett. 84 (2004) 577.
Properties of La0.75Sr0.25MnO3 films grown on Si substrate with Si1 x Gex and Si1 y Cy buffer layers Joo-Hyung Kim *, Alexander M. Grishin, Henry H. Radamson Department of Microelectronics and Information Technology, Royal Institute of Technology, SE-164 40 Stockholm-Kista, Sweden Available online 27 January 2006
Abstract The structural and electrical properties of La0.75Sr0.25MnO3 (LSMO) film on Bi4Ti3O12 (BTO)/CeO2/YSZ buffered Si1 x Gex /Si (0.05 x 0.2 for compressive strain), blank Si, and Si1 y Cy /Si ( y = 0.01 for tensile) were studied. X-ray high resolution reciprocal lattice mapping (HRRLM) and atomic force microscopy (AFM) show that structural properties of LSMO and buffer oxide layers are strongly related to the strain induced by amount of Ge and C contents. The RMS roughness of LSMO on Si1 x Gex /Si has a tendency to increase with increasing of Ge content. Electrical properties of LSMO film with Ge content up to 10% are slightly improved compared to blank Si whereas higher resistivity values were obtained for the samples with higher Ge content. D 2006 Elsevier B.V. All rights reserved. PACS: 73.50.-h Electronic transport phenomena in thin films Keywords: Manganites; Heteroepitaxial film structure on Si; Strain effect; High resolution reciprocal lattice mapping (HRRLM); Temperature coefficient of resistance (TCR)
1. Introduction High quality complex oxide films find various applications for electronic and photonic devices. Mixed-valence perovskite manganese oxides, La1 x A x MnO3 (A is Ba, Ca, Sr and Pb, 0.20 < x < 0.50) exhibit effects of colossal magnetoresistivity (CMR) and high-value temperature coefficient of resistance (TCR = 1 / RIdR / dT) due to metal (ferromagnetic phase) to insulator (paramagnetic) phase transition nearby Curie temperature, Tc. The mechanism of this phenomenon was early explained by the double-exchange interaction that the transfer of eg electron in 3d shell occurs between Mn4+ and Mn3+ ions [1]. Spin dependent metal-insulator transition in CMR materials was intensively reviewed in experiments and theoretical studies [2– 4]. Unusual electrical/magnetic properties of CMR manganites have been also considered for ferroelectric field effect transistor (FeFET), nonvolatile magnetic random access memory (MRAM) and infrared (IR) bolometric devices [5– 7]. To grow high quality CMR manganites, three relative material properties of CMR film and substrate were found to * Corresponding author. Tel.: +46 8 790 4185; fax: +46 8 752 7850. E-mail address: [email protected] (J.-H. Kim). 0040-6090/$ - see front matter D 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2005.12.222
be an important issue: lattice mismatch, different thermal expansion and chemical reaction. Lattice mismatch causes bior uniaxial strain that affects structural, electrical and magnetic properties of thin CMR films [8]. Therefore, to obtain high performance CMR manganite films one should control the strain induced from substrate. To minimize the lattice mismatch, CMR manganites were grown on oxide substrates, ˚ ) and SrTiO3 (a = 3.91 A ˚ ). Depending on as LaAlO3 (a = 3.80 A the strain, compressive in LaAlO3 or tensile in SrTiO3, different magnetic domains, feather-like or maze-like, respectively, have been observed [9]. Moreover, the electrical properties of La0.75Sr0.25MnO3 film strongly depend on film’s thickness and the type of oxide substrate [10]. Comprehensive theory of the misfit strain developed for the perovskite heteroepitaxial thin films appears to be in a good agreement with the X-ray determined out-of-plane lattice parameter c [11]. Difference in the thermal expansion coefficients of oxide films and substrate results in structural phase transformations and appearance of poly-twin domains during cooling down from the growth temperature [12]. To introduce CMR manganites to the matured semiconductor technology, the large lattice mismatch between CMR ˚ ) and semiconductor substrate manganite (a = 3.8 – 3.9 A ˚ (a = 5.431 and 5.653 A for Si and GaAs) must be overcome.
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J.-H. Kim et al. / Thin Solid Films 515 (2006) 411 – 415
tune the additional strain from tensile regime (Si1 y Cy ) to compressive regime (Si1 x Gex ) layers [14]. Fig. 1 presents the schematic of growth mechanism of Si1 y Cy and Si1 x Gex layers on Si substrates. Due to smaller lattice parameter of Si1 y Cy in Fig. 1(a) and lager lattice of Si1 x Gex than Si crystal in Fig. 1(b), the Si1 y Cy and Si1 x Gex layers on Si are under in-plane tensile and compressive strain, respectively. Therefore, using extra strained layers prior to CMR manganite film processing, the Si1 x Gex and Si1 y Cy may affect the stability of CMR film and BTO/CeO2/YSZ buffer layers. Here, we investigate the strain effect of Si1 x Gex (for extra compressive) and Si1 y Cy (for tensile) layers on structural and electrical properties of La0.75Sr0.25MnO3 (LSMO) films grown under the same optimized deposition conditions on BTO/CeO2/YSZ buffered Si substrates. 2. Experimental details
Fig. 1. Schematic of (a) Si1 y Cy and (b) Si1 x Gex layers on Si substrates.
YSZ and CeO2/YSZ are commonly used for buffer layers on Si substrate. In our previous report, high quality epitaxial La0.67(Sr,Ca)0.33MnO3 films on Si substrates with Bi4Ti3O12(BTO)/CeO2/YSZ buffer layers were successfully grown for bolometric applications [13]. But until now, there are very few reports for systematic studies of strain effect between CMR films and Si substrate. For this purpose, Si1 x Gex and Si1 y Cy layers can be directly applied on Si substrate with an appropriate Ge and C amount to
Si1 x Gex (x = 0.05 –0.20) and Si1 y Cy ( y = 0.01) films were grown on Si (100) substrates at 650 and 575 -C correspondingly, by reduced pressure chemical vapor deposition (RPCVD, Epsilon 2000) technique using the N2 purged loadlock to minimize O2 contamination. To create Si1 x Gex layers on Si substrate, silane (SiH4) and germane (GeH4) were supplied for silicon and germanium precursors with H2 carrier gas. For Si1 y Cy layer, silane and methyl-silane (SiH3CH3) were added. Because epitaxial film growth is very sensitive to surface condition of substrate, all of Si wafer were chemically cleaned before loading into RPCVD chamber. The Ge content and thickness of Si1 x Gex and Si1 y Cy layers were calculated from the high-resolution X-ray diffraction (HRXRD) patterns. The deposited Si1 x Gex and Si0.99C0.01 layer thicknesses were ˚ . After deposition of BTO around 1030¨1200 and 1200 A ˚ ˚ ˚ ) buffer layers, 500 A ˚ (1000 A) / CeO2(400 A) / YSZ (300 A thick LSMO films were sintered by KrF pulsed laser deposition (PLD) method at 750 -C, 0.4 Torr of O2 on the Si1 x Gex /Si, Si and Si0.99C0.01/Si substrates. After films’
Fig. 2. Rocking curves around (004) Bragg reflection of as-grown Si1 y Cy /Si and Si1 x Gex /Si. The arrows indicate main peaks of Si1 y Cy /Si and Si1 x Gex /Si layers.
J.-H. Kim et al. / Thin Solid Films 515 (2006) 411 – 415
413
Fig. 3. Reciprocal lattice mappings of heteroepitaxial La0.75Sr0.25MnO3/Bi4Ti3O12/CeO2/YSZ films on (a) Si0.99C0.01/Si, (b) Si, (c) Si0.9Ge0.1/Si, and (d) Si0.8Ge0.2/Si substrates.
growth, in situ post annealing was executed at 730 -C in 500 Torr of O2 for 5 min. More details of deposition conditions can be found elsewhere [13]. The structural quality and surface morphology of all samples were investigated by high resolution reciprocal lattice mapping (HRRLM), HRXRD and atomic force microscopy (AFM, Nanoscope Dimension 3100). Temperature-dependant electrical properties of LSMO
films on different strained substrates were measured by fourprobe technique. 3. Results and discussion Fig. 2 shows rocking curves recorded by HRXRD around Si (004) Bragg reflection of as-grown Si1 x Gex /Si, and Si0.99C0.01/
Fig. 4. Surface morphology of Bi4Ti3O12/CeO2/YSZ buffered La0.75Sr0.25MnO3 films on (a) Si0.99C0.01/Si, (b) Si, (c) Si0.9Ge0.1/Si, and (d) Si0.8Ge0.2/Si.
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J.-H. Kim et al. / Thin Solid Films 515 (2006) 411 – 415
Fig. 5. Temperature-dependent resistivity and corresponding temperature coefficient of resistance (TCR) of LSMO films on Si1 x Gex /Si and Si.
Si. Here, LSMO film on Si substrate was considered as a reference sample for the strained Si1 x Gex /Si and Si0.99C0.01/Si structures. From the rocking curves, main peak positions and fringes of all Si1 x Gex and Si0.99C0.01 layers on Si are clearly observed. The estimated lattice parameters of Si0.99C0.01, Si0.95Ge0.05, Si0.9Ge0.1 and Si0.8Ge0.2 layers were 5.395, 5.441, ˚ , respectively. The arrows in Fig. 2 represent 5.451 and 5.472 A main peaks of grown Si1 x Gex and Si0.99C0.01 layers. After deposition of heteroepitaxial LSMO/BTO/CeO2/YSZ structure on strained Si1 x Gex /Si and Si0.99C0.01/Si, the full width half maximum (FWHM) of LSMO-002 Bragg reflection of all samples are 1.10- 0.85-, 0.81- and 1.10- for Si0.99C0.01/ Si, Si, Si0.9Ge0.1/Si and Si0.8Ge0.2/Si, respectively. For detailed investigation of structural relation between the layers, HRRLM around (004) reflection was performed [15]. All of layers including substrate are distinguished by peak position in Fig. 3. In these maps, there is a clear difference in the intensity of the main contours and the shape of BTO-0022 and LSMO-003 peaks between Fig. 3(b) and (d). The shape of BTO-0022 peak changes from ellipsoid in Si0.8Ge0.2 and Si0.99C0.01 samples to a rhombic for Si0.9Ge0.1 and Si samples. There is no change of c lattice parameter observed since no shift in the peak position. Therefore, the changes of the BTO0022 shape stem from alteration between a and b lattice parameters due to biaxial strain change [16]. Fig. 4 shows surface morphology of all PLD-grown LSMO samples recorded in tapping mode AFM measurements. The scan area and rate during measurements were 2 2 Am2 and 1 Hz, respectively. Root mean square (RMS) surface roughness ˚ for Si0.95Ge0.05/Si, of LSMO films was 16.1, 18.0 and 18.6 A Si0.9Ge0.1/Si and Si0.8Ge0.2/Si, respectively. These results indicate that the roughness of LSMO layers on Si1 x Gex /Si has a tendency to increase with increasing of Ge content and is related to extra compressive strain. However, the surface of LSMO film on Si0.99C0.01/Si, under excessive tensile strain, has ˚. the lowest value of RMS roughness, 14.1 A
For electrical measurements, normalized temperature-dependent resistivity is presented in Fig. 5. All curves of LSMO films on Si1 x Gex /Si, except Si0.8Ge0.2/Si, show similar electrical characteristics whereas Si0.99C0.0.1/Si, not shown here, exhibits very large resistivity, q max = 126 kV I cm. There is a slight improvement in TCR value of Si0.9Ge0.1/Si compared to Si. 4. Conclusions Structural and electrical properties of La0.75Sr0.25MnO3 films on Bi4Ti3O12/CeO2/YSZ buffered Si1 x Gex /Si (0.05 x 0.2), Si, and Si0.99C0.01/Si were investigated to understand strain effects. For Si1 x Gex /Si, the shape of reciprocal lattice maps of Bi4Ti3O12(0022) Bragg reflections is strongly related to LSMO film quality, varies from rhombic to elliptic one due to modification of a and b lattice parameters. The RMS roughness of LSMO on Si1 x Gex /Si is dependent on Ge content. LSMO films on Si0.8Ge0.2/Si and Si0.99C0.01/Si show higher resistivity and low TCR values compared to Si sample due to excessive compressive and tensile strain, respectively. References [1] C. Zener, Phys. Rev. 82 (1951) 403. [2] E.O. Wollan, W.C. Koehler, Phys. Rev. 100 (1995) 545. [3] Y. Morimoto, A. Asamitsu, H. Kuwahara, Y. Tokura, Nature 380 (1996) 141. [4] A.J. Millis, B.I. Shraiman, R. Mueller, Phys. Rev. Lett. 77 (1996) 175. [5] T. Venkatesan, M. Rajeswari, Zi-Wen Dong, S.B. Ogale, R. Ramesh, Phil. Trans. R. Soc. Lond., A 356 (1998) 1661. [6] Y. Lu, X.W. Li, G.Q. Gong, G. Xiao, A. Gupta, P. Lecoeur, J.Z. Sun, Y.Y. Wang, V.P. Dravid, Phys. Rev., B 54 (1996) R8357. [7] A. Lisauskas, S.I. Khartsev, A. Grishin, Appl. Phys. Lett. 77 (2000) 756; A. Lisauskas, S.I. Khartsev, A. Grishin, Appl. Phys. Lett. 77 (2000) 3302. [8] Joonghoe Dho, Y.N. Kim, Y.S. Hwang, J.C. Kim, N.H. Hur, Appl. Phys. Lett. 82 (2003) 1434. [9] C. Kwon, M.C. Robson, K.-C. Kim, J.Y. Gu, S.E. Loftland, S.M. Bhaget, Z. Trajanovic¸, M. Rajeswari, T. Venkatesan, A.R. Kratz, R.D. Gomez, R. Ramesh, J. Magn. Magn. Mater. 172 (1997) 229.
J.-H. Kim et al. / Thin Solid Films 515 (2006) 411 – 415 [10] S.I. Khartsev, P. Johnsson, A.M. Grishin, J. Appl. Phys. 87 (2000) 2394. [11] C.L. Canedy, H. Li, S.P. Alpay, L. Salamance-Riba, A.L. Roytburd, R. Ramesh, Appl. Phys. Lett. 77 (2000) 1695. [12] S.P. Alpay, A.L. Roytburd, J. Appl. Phys. 83 (1998) 4714. [13] J.-H. Kim, S.I. Khartsev, A.M. Grishin, Appl. Phys. Lett. 82 (2003) 4295.
415
[14] J.P. Dismukes, L. Ekstrom, R.J. Paff, J. Phys. Chem. 68 (1964) 3021. [15] E. Koppensteiner, G. Bauer, H. Kibbel, E. Kasper, J. Appl. Phys. 76 (1994) 3489. [16] Y. Lin, X. Chen, S.W. Liu, C.L. Chen, Jang-Sik Lee, Y. Lee, Q.X. Jia, A. Bhalla, Appl. Phys. Lett. 84 (2004) 577.