Highly oriented metallic SmS films on Si(100) grown by pulsed laser deposition A.V. Zenkevich a,b, ⁎, O.E. Parfenov b , V.G. Storchak b , P.E. Teterin a , Yu.Yu. Lebedinskii a,b a National Research Nuclear University “Moscow Engineering Physics Institute,” Moscow 115409, Russia b Russian Research Center “Kurchatov Institute,” NBIC Center, Moscow 123182, Russia abstract article info Article history: Received 14 October 2010 Received in revised form 31 March 2011 Accepted 5 April 2011 Available online 13 April 2011 Keywords: Samarium sulfide Thin films Metal/dielectric phase transition Pulsed laser deposition Si(100) Stoichiometric and highly oriented in (100) direction SmS films in the metallic phase have been grown on Si(100) substrate at room temperature by pulsed laser deposition (PLD) as revealed from lattice parameter, reflectivity and electrical resistivity measurements. Above-critical compressive stress P =0.9 GPa in as grown film was determined from sample curvature measurements and attributed to stress building up in PLD process further accompanied by stress due to SmS versus Si lattice parameter mismatch. Stress relaxation and subsequent metal-to-semiconductor phase transition occurred following annealing at T =900 K as evident from consistent changes of SmS/Si sample curvature, structural, optical and electrical properties. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Samarium monosulfide (SmS) is well known for the pressure- induced reversible first-order semiconductor to metal phase transi- tion [1] which can be utilized to design switching and non-volatile memory devices. The low pressure semiconducting phase can be converted to the metallic phase upon applying pressure P = 0.65 GPa without the change of SmS rocksalt crystal structure and is accompanied by the sharp decrease of the lattice constant from a = 0.597 nm to a ≈0.570 nm [2]. The isostructural phase transition is attributed to the Sm ion valence electron transitions: with an increase in pressure, the Sm 4 f levels and the Sm 5d conduction band begin to overlap which eventually results in the delocalization of 4f electrons and the emergence of metallic conductivity (4 f 6 d 0 -4 f 5 d 1 )[3]. Originally discov- ered in the bulk SmS under isotropic pressure, the phase transition was later observed upon hard polishing of the semiconducting SmS single crystal surface [1,4] or polycrystalline thin film [5] which produces sufficient internal stress to convert the surface layer into the metallic phase stable at room temperature. The annealing results in the reverse transition to the semiconducting phase. Alternatively, the stress imposed by partial substitution of Sm ion in SmS with another rare earth metal (e.g. Gd) forming monosulfide with a smaller lattice parameter—the so-called chemical pressure effect—was shown to produce the same effect as applying pressure [6]. Since the discovery of the phase transition, the growth of both semiconductor and metal phase polycrystalline SmS thin films have been reported [5,7–11]. However the role of the substrate, particularly, the possibility to affect the phase formation in SmS by selecting the favorable surface crystalline structure has not been investigated so far. SmS possesses the cubic structure and its lattice parameter in the metallic phase a ≤ 0.57 nm [2] is only about 4% larger compared to Si (a =0.543 nm). The lattice mismatch between the film and substrate can thus induce the stress in the film sufficient to stabilize the metal phase provided that SmS film grows coherently on the Si substrate. In this work, we report on the growth of stoichiometric, highly oriented metallic SmS thin films on the clean Si(100) substrate at room temperature by pulsed laser deposition (PLD). The technique is known to modify the stress in the film due to the impact of energetic species in the condensing flux [12]. We argue that such effect combined with the lattice mismatch between the film and the substrate is responsible for the formation of the stable metallic SmS phase at low ambient pressure. Subsequent annealing of SmS/Si(100) structure results in the stress relaxation in SmS film evident from the curvature measurements and its isostructural transition to the semiconducting phase. 2. Experimental details SmS thin films were grown by PLD in an ultra high vacuum (UHV) setup with the base pressure P ≈10 −6 Pa. YAG:Nd laser (λ = 1064 nm), operating in the Q-switched regime (τ = 15 ns) with the variable output energy E =50÷200 mJ and the pulse repetition rate ν =5–50 Hz, was used to ablate the stoichiometric SmS target. The target was prepared by press forming of the stoichiometric SmS powder into a pellet of 7 mm diameter. The annealing of as grown samples in the temperature range T = 600–1000 K was performed in the same UHV chamber. The Si(100) wafers 1×1 cm in size with the oxide layer chemically etched in Thin Solid Films 519 (2011) 6323–6325 ⁎ Corresponding author. E-mail address: avzenkevich@mephi.ru (A.V. Zenkevich). 0040-6090/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2011.04.015 Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf