Properties of La 0.7 Sr 0.3 MnO 3 thin ®lms grown on gallium nitrides D.-W. Kim a , D.H. Kim a , T.W. Noh a, * , E. Oh b , H.C. Kim c , H.-C. Lee c a School of Physics and Research Center for Oxide Electronics, Seoul National University, Seoul 151-747, South Korea b Brain Korea 21 Physics Research Division, Seoul National University, Seoul, South Korea c Material Science Laboratory, Korea Basic Science Institute, Taejon 305-333, South Korea Received 30 October 2001; accepted 10 December 2001 by C.N.R. Rao Abstract Polycrystalline La 0.7 Sr 0.3 MnO 3 (LSMO) thin ®lms were grown on GaN layers by pulsed laser deposition. High quality LSMO ®lms could be prepared without the aid of buffer layers. Ferromagnetic transition temperature of a 500 A Ê thick LSMO/GaN ®lm was as high as 330 K and coercive ®eld was less than 20 Oe at room temperature. Current±voltage measurements of LSMO/ GaN contacts showed a clear rectifying behavior, which might be caused by Schottky barrier formation at the interfaces. The LSMO/GaN hybrid can be a candidate for spin-injectors, which will be useful for room temperature and low ®eld applications. q 2002 Published by Elsevier Science Ltd. PACS: 73.40.Cg; 75.70.Pa; 81.15.Fg; 85.80.Jm Keywords: A. Magnetic ®lms and multilayers; A. Semiconductors; D. Electronic transport Spin-polarized carrier injection into semiconductors has attracted much attention during the last few years for possible device applications such as magnetic storage in semiconductors and spin transistors [1]. Electrical spin injection into a non-magnetic semiconductor has been successfully demonstrated by making use of a ferromagnetic metal [2]. However, until now the spin polarization in such a hybrid remains within a few percent. Schmidt et al. attributed the limited ef®ciency to the large conductivity mismatch between the ferromagnetic metals and semi- conductors [3]. Colossal magnetoresistance (CMR) materials can be alternative candidates for ef®cient spin- injectors with their resistivities being comparable to those of semiconductors [4,5] and they are known to have nearly 100% spin polarizations [6]. However, there was no report related to the electrical properties of the CMR/semiconduc- tor interface, as far as we know [7±9]. In the case of Si substrates, CMR thin ®lms have been grown on insulating buffer layers to suppress serious chemical reaction at the interfaces [7±10] and hence transport across the barrier is expected to be dif®cult. To fabricate CMR/semiconductor hybrids, La 0.7 Sr 0.3 MnO 3 (LSMO) ®lms were prepared on GaN layers. Among the CMR materials, LSMO has relatively high ferromagnetic transition temperature (T C ) of 370 K [5]. GaN has superior thermal stability compared to those of other semiconductors [11] and ferromagnetic ®lms grown on GaN-based two dimensional electron gas (2DEG) structures could be useful for future spin transistors [12]. Based on such expectations, we investigated the physical properties of LSMO/GaN heterostructures. GaN layers were grown on sapphire (Al 2 O 3 ) substrates by metal±organic chemical vapor phase epitaxy. LSMO ®lms were grown on the GaN layers by the pulsed laser deposition technique using a KrF excimer laser l  248 nm: The substrate temperature and the oxygen pressure were 750 8C and 10 mTorr, respectively. After deposition, the ®lms were annealed in situ at 600 8C in 400 Torr of oxygen ambient. X-ray diffraction (XRD) measurements of a 500 A Ê thick LSMO ®lm grown on a GaN layer showed that the ®lm is polycrystalline. GaN has the wu Èrtzite structure with hexagonal symmetry (a  3:186 and c  5.178 A Ê ) and LSMO has the perovskite-type structure with cubic sym- metry (a  3.87 A Ê ). Under the same conditions, LSMO ®lm was also grown on a Al 2 O 3 substrate, which has the corundum type structure with hexagonal symmetry (a  4.76 A Ê and c  12.99 A Ê ). The LSMO/Al 2 O 3 ®lm was also polycrystalline and this implied that the crystalline Solid State Communications 121 (2002) 631±634 0038-1098/02/$ - see front matter q 2002 Published by Elsevier Science Ltd. PII: S0038-1098(02)00033-9 PERGAMON www.elsevier.com/locate/ssc * Corresponding author. Tel.: 182-2-880-6616; fax: 182-2-875- 1222. E-mail address: twnoh@phya.snu.ac.kr (T.W. Noh).