We report on the integration of epitaxial colossal magnetoresistive La0.67Ba0.33MnO films on Si(100) semiconductor using SrTiO3 template layer by pulsed-laser deposition. X-ray diffraction reveals the superior quality of the manganite film that grows epitaxially on heteroepitaxially grown SrTiO3 template layer on Si substrate. The epitaxial films demonstrate remarkable surface morphology, magnetic transition and hysteresis, magnetoresistance, and ferromagnetic resonance, illustrating the ferromagnetic nature of the film and possible device applications at room temperature

Dadson, J.B.

Hunter, D.

Jackson, E.M.

Loutts, G.B.

Mohanty, S.

Pradhan, Aswini K.

Rakhimov, Rakhim R.

Sellmyer, David J.

Zhang, Jun

Zhang, Kai

English

DigitalCommons@University of Nebraska

University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln David Sellmyer Publications Research Papers in Physics and Astronomy 1-3-2005 Integration of epitaxial colossal magnetoresistive films onto Si(100) using SrTiO3 as a template layer Aswini K. Pradhan Center for Materials Research, Norfolk State University, apradhan@nsu.edu S. Mohanty Center for Materials Research, Norfolk State University, Norfolk, Virginia Kai Zhang Center for Materials Research, Norfolk State University, Norfolk, Virginia J.B. Dadson Center for Materials Research, Norfolk State University, Norfolk, Virginia E.M. Jackson Center for Materials Research, Norfolk State University, Norfolk, Virginia See next page for additional authors Follow this and additional works at: https://digitalcommons.unl.edu/physicssellmyer  Part of the Physics Commons Pradhan, Aswini K.; Mohanty, S.; Zhang, Kai; Dadson, J.B.; Jackson, E.M.; Hunter, D.; Rakhimov, Rakhim R.; Loutts, G.B.; Zhang, Jun; and Sellmyer, David J., "Integration of epitaxial colossal magnetoresistive films onto Si(100) using SrTiO3 as a template layer" (2005). David Sellmyer Publications. 27. https://digitalcommons.unl.edu/physicssellmyer/27 This Article is brought to you for free and open access by the Research Papers in Physics and Astronomy at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in David Sellmyer Publications by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Authors Aswini K. Pradhan, S. Mohanty, Kai Zhang, J.B. Dadson, E.M. Jackson, D. Hunter, Rakhim R. Rakhimov, G.B. Loutts, Jun Zhang, and David J. Sellmyer This article is available at DigitalCommons@University of Nebraska - Lincoln: https://digitalcommons.unl.edu/physicssellmyer/27 Integration of epitaxial colossal magnetoresistive films onto Si (100) usingSrTiO 3 as a template layerA. K. Pradhan,a) S. Mohanty, Kai Zhang, J. B. Dadson, E. M. Jackson, D. Hunter,R. R. Rakhimov, and G. B. LouttsCenter for Materials Research, Norfolk State University, 700 Park Avenue, Norfolk, Virginia 23504Jun Zhang and D. J. SellmyerDepartment of Physics and Astronomy and Center for Materials Research and Analysis,University of Nebraska, Lincoln, Nebraska 68588-0113(Received 15 July 2004; accepted 29 October 2004; published online 23 December 2004)We report on the integration of epitaxial colossal magnetoresistive La0.67B 0.33MnO films on Si(100)semiconductor using SrTiO3 template layer by pulsed-laser deposition. X-ray diffraction reveals thesuperior quality of the manganite film that grows epitaxially on heteroepitaxially grown SrTiO3template layer on Si substrate. The epitaxial films demonstrate remarkable surface morphology,magnetic transition and hysteresis, magnetoresistance, and ferromagnetic resonance, illustrating theferromagnetic nature of the film and possible device applications at room temperature. ©2005American Institute of Physics. [DOI: 10.1063/1.1842852]There has been a considerable research interest recentlyto integrate perovskite-type oxide thin films onto Si, not onlyto meet the ever-shrinking size of the metal-oxide-semiconductor field-effect transistors(FETs) for applicationas alternative high-k gate dielectrics, devices such as dy-namic random access memories, ferroelectric nonvolatilememories, but also a template layer to integrate other per-ovskites, such as lanthanum-based colossal magnetoresistive(CMR) oxides onto Si for application in FETs for spintronic,high-density magnetic memory, sensors, and infraredbolometers1–8 at ambient temperature. Among all reportedhigh-k materials, perovskite-type SrTiO3 (STO) lends itselfone of the most potential materials for an alternative gatedielectric if high-quality epitaxial STO films are grown onSi. STO has a simple cubic structure withk=300 at roomtemperature and the lattice mismatch between STOsa0=3.905 Åd and Si sa0=5.431 Åd is reasonably smalls,1.7%d with STO unit cell rotated 45° around Si surfacenormal to[001] axis. STO films of very high structural qual-ity are deposited by molecular-beam epitaxy8 and the avail-ability of such high-quality [001] perovskite-terminatedSi[100] substrates provides numerous opportunities for inte-gration of other technologically important perovskites, suchas CMR, on a surface of high crystalline quality.While perovskite lanthanum-based manganite(R1−xBxMnO3 where R and B are rare-earth and alkali met-als, respectively) films have been successfully grown onsingle-crystal oxide substrates, such as STO, LaAlO3, andNdGaO3, the growth on Si is very limited.8 It is also of agreat importance to integrate an IR detector array withcomplementary metal-oxide-semiconductor readout as wellas FET architecture on the same Si wafer. However, the re-sults achieved on Si are very limited. In order to grow anepitaxial quality manganite film, the film–substrate latticemismatch needs to be minimized, the film–substrate thermalexpansion coefficients have to be matched, and the chemicalreaction between the substrate and deposited film should beeliminated. Although Si does not comply with all these re-quirements, introducing a template layer can accommodatemechanical and chemical disaccords. Furthermore, the biax-ial strain due to lattice mismatch between film and substratethat plays a dominant role for the electronic phase separationand it modifies the charged ordered state in CMRmaterials.7,8 This lattice strain induced by the substrate inepitaxial films of these materials can be used as a good pa-rameter for tuning the physical properties through the mutualcoupling of the lattice degree of freedom to the charge, spin,and orbital degrees of freedom.9–12 However, integrating themanganites onto the semiconducting materials such as Si,GaAs, and GaN remains a challenging task for potential de-vice applications that utilize both information processing anddata storage in the same device. Recent progress on directintegration8,13 of STO on Si has opened a possibility to inte-grate both STO and R1−xBxMnO3 onto this technologicallyimportant semiconductor. In this letter, we report fabricationof superior-quality La0.67Ba0.33MnO [(LBMO)/STO/Si(001)]heterostructures, using pulsed-laser deposition(PLD), whichdemonstrate remarkable structural, microscopic, and mag-netic properties in the vicinity of room temperature. We havedemonstrated highly epitaxial growth of LBMO on Si usinga heteroepitaxially grown STO template layer.LBMO/STO/Si(100) epitaxial films were grown by amultitarget PLD technique(KrF excimer,l=248 nm) with apulse energy density of 1–2 J/cm2 and utilizing both targetrotation and rastering, and substrate rotation facilities. Singlecrystalline STO and high-density LBMO targets were used.LBMO calcined powders were isostatically pressed at400 MPa and sintered at 1450 °C in order to make a high-density target. The films were deposited on clean Si(100)substrates with a substrate temperature 700–800 °C, keep-ing oxygen partial pressure of 200 to 400 mTorr. The sub-strate was loaded to the chamber using load-lock facility at-tached to the chamber, and heated in the chamber just afterthe ultimate base pressure,4310−8 Torr to avoid the oxi-dation of the substrate. For STO/Si growth, the initial2-nm-thick growth of STO film was carried out without us-ing oxygen gas, and subsequently 18-nm-thick film of STOa)Author to whom all correspondence should be addressed; electronic mail:apradhan@nsu.eduAPPLIED PHYSICS LETTERS86, 012503(2005)0003-6951/2005/86(1)/012503/3/$22.50 © 2005 American Institute of Physics86, 012503-1Downloaded 14 Nov 2006 to 129.93.16.206. Redistribution subject to AIP license or copyright, see http://apl.aip.org/apl/copyright.jspon Si was deposited with oxygen partial pressure of 1 mTorrwith laser repetition rate of 3 Hz. Several batches of STO/Sifilms were grown in order to optimize the best condition toobtain good-quality epitaxial film. LBMO film of 50 nm wasimmediately deposited in oxygen partial pressure on STO/Siusing a laser repetition rate of 5 Hz. The film was cooled in1 Torr of oxygen partial pressure to room temperature. Thex-ray diffraction (XRD) of the films was done in a Rigakux-ray diffractometer using Cu Ka radiation. The zero-field-cooled magnetizationsMd and hysteresis measurements werecarried out down to 5 K using a superconducting quantuminterference device magnetometer(Quantum Design), andthe resistivity measurements were done with a four-probetechnique. The ferromagnetic resonance(FMR) experimentswere done in a Bruker EMS spectrometer operating at 9.6GHz microwave frequency.Figure 1 shows the XRD patterns of STO/Si and LBMO/STO/Si films. The XRD of the STO/Si heterostructure re-veals strongsl00d orientations. However, a strong STO(110)orientation was also observed. The orientation relationshipbetween the STO thin film and the Si(001) substrate in theSTO/Si heterostructure is described13,14ass001dSTO/ / s001dSiand s100dSTO/ / s110dSi, which means the STO lattice is ro-tated by 45° around the[001] axis of the Si lattice on theSi(001) surface. The lattice misfit parameter between Si(110)s3.82 Åd and STOs3.905 Åd is about 1.67%, which is rea-sonably small14 between the parallel interfaces and could in-duce very small strain. The observation of a strong STO(110)orientation is favored for the growth of STO/Si heterostruc-ture due to similar lattice matching. A strong satellite reflec-tion of s011dSTO was seen in the selected area electron dif-fraction pattern14 taken from an interface region, illustratingthe orientation relationship ofs100dSTO/ / s110dSi. In LBMO/STO/Si heterostructures, LBMO preferred energetically togrow epitaxially only in(110) orientation ons110dSTO direc-tion due to reduced strain as shown in the bottom of Fig. 1.The rocking curve of epitaxial growth of LBMO ons110dSTOis shown in the inset of Fig. 1. The full widths at half-maximum of STO(110) and LBMO(110) are about 0.3° and0.1°, respectively, which illustrate the highly crystalline na-ture of the film.In order to compare the surface morphology of STO/Siand LBMO/STO/Si films, atomic force microscopic(AFM)images are shown in Figs. 2(a)–2(d). The atomically flat anddefect-free surface morphology with rms surface roughnessof less than 2 nm was seen in STO/Si film. Surprisingly,closer inspection of the AFM images of STO/Si reveals het-eroepitaxial growth on the surface. However, LBMO/STO/Sifilm shows very uniform and epitaxial surface morphologywith similar surface roughness and crystallite size,20 nm.These studies suggest good crystallinity and epitaxy in allfilms.In Fig. 3(a), the zero-field-cooled temperature depen-dence of magnetization is shown for LBMO/STO/Si film in afield of 0.1 T. The magnetic transitions are fairly sharp withTc onset at 320 K, as shown in the top inset of Fig. 3(a). Thefilms demonstrate ferromagnetic hysteresis at 300 K with aferromagnetic saturation field of about 4 KOe, as shown inthe inset of Fig. 3. The temperature and magnetic field de-pendence of resistivityr show a remarkably sharp jump atthe metal–insulator transition temperaturesTMId as shown inFig. 3(b), which is consistent with the magnetic transition.The TMI is remarkably sharp, and the calculated value oftemperature coefficient of resistivity[TCR=1/r dr /dT<20% at TMI, as shown in the inset of Fig. 3(b)] is verymuch relevant for the required value for the bolometric ap-plications. The resistivity is significantly reduced at the tran-sition with the magnetic field due to spin alignment. How-ever, the onset ofTc is slightly higher compared to the filmsgrown directly on STO substrates.6,15 The Tc value for x=0.33 film is about 305 K compared to that of its bulk, withTc=345 K. The difference inTc in films compared to theirbulk counterpart is certainly attributed to the type of straindeveloped between the films and the substrates. The role ofthe strain-induced modification of thedx2−y2 orbital stabilityresulting from in-plane Mn-O distance determines theTc ofFIG. 1. XRD patterns of STO/Si(100) (top) and LBMO/STO/Si(bottom)heterostructures. The inset(bottom) shows the rocking curve XRD patternof LBMO/STO/Si heterostructures, showing growth of LBMO on STO tem-plate layer gown on Si.FIG. 2. AFM images of(a) and(b) STO/Si, and(c) and(d) LBMO/STO/Siheterostructures. All images are 2mm32 mm in size.012503-2 Pradhan et al. Appl. Phys. Lett. 86, 012503 (2005)Downloaded 14 Nov 2006 to 129.93.16.206. Redistribution subject to AIP license or copyright, see http://apl.aip.org/apl/copyright.jspLBMO6,12 through Mn3+-O-Mn4+ double-exchange mecha-nism. As a consequence, the effective in-plane charge densitydecreases in case of compressive strain. It has been shown12that the lattice mismatch induces compressive-type strain forx=0.33sc/a<0.15%d, which is responsible for reducingTcin LBMO films, contrary to other CMR material. However,the superior nano-crystallinity, epitaxial nature of LBMO/STO/Si film, and especially the epitaxial STO template layercan minimize the strain effect through strain relaxation forenhanced transition. There remain enough scopes to mini-mize the interface disorders and to enhance the oxygenationto markedly enhance the physical properties in the vicinity ofroom temperature.It is also remarkable to note that the heterostructuresdisplay a pronounced ferromagnetic resonance at room tem-perature[Fig. 3(c)]. The spectra present a characteristic fea-ture centered at aboutg=2. However, the resonant field po-sition changes with angle between the film surface and theapplied magnetic field, indicating the anisotropic behavior ofthe epitaxial film. Although the effective demagnetizationfield, 4pMeff=4pMs−2Ku/Ms (whereMs is saturation mag-netization andKu is anisotropy energy density perpendicularto the film plane) is different, the variation could arise fromdifferent residual stress in the film. The present FMR signalis mainly from the Mn4+ ions, which is close tog=1.994,since the contribution from Mn3+ ions is unlikely to producean observable signal due to their large zero-field splitting andstrong spin-lattice relaxation.16It is anticipated that further optimization of the growthprocess may enhance the magnetic properties of the hetero-structure significantly. Our studies are significantly differentfrom other reports7,8 wherein manganites films are grown onSi using several buffer layers. However, the present LBMO/STO/Si heterostructures are unique in the sense that bothmanganites and STO could lead to multifunctionalities forvarious technological applications.In summary, we have demonstrated the fabrication andhigh performance of epitaxial manganite films grown on Sisubstrates using SrTiO3 as a template layer with aTc tuned toroom temperature. The epitaxial films demonstrate remark-able surface morphology, magnetic hysteresis, magnetic tran-sition, and ferromagnetic resonance at room temperature, il-lustrating the ferromagnetic nature of the film. Our resultsdemonstrate the scope of the integration of epitaxial manga-nite films on semiconducting substrates, such as Si, and canbe extended to other potential semiconductors, such as GaNand GaAs, using appropriate template/buffer layers. This willproduce many generic approaches to the integration of mul-ticomponent oxide thin films on semiconducting surfaces,which can impact a variety of technologies.This work is supported by the National Aeronautics andSpace Administration and University Research Center coop-erative agreement NCC-3-1035 and National Science Foun-dation for Center for Research Excellence in Science andTechnology grant no. HRD-9805059. One of the authors(R.R.R.) acknowledges the support from the faculty researchprogram provided by NASA. Research at the University ofNebraska is supported by NSF-MRSEC, ONR, and CMRA.Authors are thankful to A. Wilkerson for experimental help.1A. Goyal, M. Rajeswari, R. Shreekala, S. E. Lofland, S. M. Bhagat, T.Boettcher, C. Kwon, R. Ramesh, and T. Venkatesan, Appl. Phys. Lett.71,2535 (1997).2M. Rajeswari, C. H. Chen, A. Goyal, C. Kwon, M. C. Robson, R. Ramesh,T. Venkatesan, and S. Lakeou, Appl. Phys. Lett.68, 3555(1996).3S. Mathews, R. Ramesh, T. Venkatesan, and J. Benedetto, Science276,3790 (1997).4M. Rajeswari, R. Shreekala, A. Goyal, S. E. Lofland, S. M. Bhagat, K.Ghosh, R. P. Shaema, R. L. Greene, R. Ramesh, and T. Venkatesan, Appl.Phys. Lett. 73, 2672(1998).5R. von Helmolt, J. Wecker, B. Holzapfel, L. Schultz, and K. Samwer,Phys. Rev. Lett.71, 2331(1993); S. Jin, T. H. Tiefel, M. McCormack, R.A. Fastnacht, and R. Ramesh, Science264, 413 (1994).6A. K. Pradhan, D. Sahu, B. K. Roul, and Y. Feng, Appl. Phys. Lett.81,3597 (2002).7T. Zhao, S. B. Ogale, S. R. Shinde, R. Ramesh, R. Droopad, J. Yu, K.Eisenbeiser, and J. Misewich, Appl. Phys. Lett.84, 750 (2004).8J.-H. Kim, S. I. Khartsev, and M. Grishin, Appl. Phys. Lett.82, 4295(2003), and references therein.9Y. Suzuki, H. Y. Hwang, S.-W. Cheong, and R. B. van Dover, Appl. Phys.Lett. 71, 140 (1997); F. Tsui, M. C. Smoak, T. K. Nath, and C. B. Eom,ibid. 76, 2421(2000).10Y. Ogimoto, M. Izumi, T. Manako, T. Kimura, Y. Tomioka, M. Kawasaki,and Y. Tokura, Appl. Phys. Lett.78, 3505(2001).11E. R. Buzin, W. Prellier, Ch. Simon, S. Mercone, B. Mercey, B. Raveau, J.Sebek, and J. Hejtmanek, Appl. Phys. Lett.79, 647 (2001).12J. Zhang, H. Tanaka, T. Kanki, J.-H. Choi, and T. Kawai, Phys. Rev. B64,184404(2001).13Y. Wang, C. Ganpule, B. T. Liu, H. Li, K. Mori, B. Hill, M. Wuttig, R.Ramesh, J. Finder, Z. Yu, R. Droopad, and K. Eisenbeiser, Appl. Phys.Lett. 80, 97 (2002), and references therein.14G. Y. Yang, J. M. Finder, J. Wang, Z. L. Wang, Z. Yu, J. Ramdani, R.Droopad, K. W. Eisenbeiser, and R. Ramesh, J. Mater. Res.17, 204(2002).15A. K. Pradhan, D. Sahu, B. K. Roul, and Y. Feng, J. Appl. Phys.96, 1170(2004).16A. Shengelaya, G. M. Zhao, H. Keller, and F. A. Muller, Phys. Rev. Lett.77, 5296(1996).FIG. 3. (a) Temperature-dependent zero-field-cooled magnetization ofLBMO/STO/Si film for a magnetic field of 0.1 T. The top inset showsdM /dT vs temperature. The bottom inset shows magnetization hysteresisloops of film at room temperature, illustrating ferromagnetic behavior.(b)The temperature dependence of resistivity of LBMO/STO/Si film in 0 T and1 T magnetic fields. The inset in(b) shows the TCR(%) as function oftemperature.(c) Ferromagnetic resonance spectra of LBMO/STO/Si film atroom temperature for two angles.012503-3 Pradhan et al. Appl. Phys. Lett. 86, 012503 (2005)Downloaded 14 Nov 2006 to 129.93.16.206. Redistribution subject to AIP license or copyright, see http://apl.aip.org/apl/copyright.jsp

Integration of epitaxial colossal magnetoresistive films onto Si(100) using SrTiO\u3csub\u3e3\u3c/sub\u3e as a template layer

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Integration of epitaxial colossal magnetoresistive films onto Si(100) using SrTiO\u3csub\u3e3\u3c/sub\u3e as a template layer

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