Epitaxial growth of skutterudite (CoSb 3 ) thin films on (001) InSb by pulsed laser deposition
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J.S. Harper, R. Gronsky, and T. Sandsa) Department of Materials Science and Engineering, University of California, Berkeley, California 94720 (Received 6 November 2000; accepted 2 July 2001)
Heteroepitaxial growth of the cubic skutterudite phase CoSb3 on (001) InSb substrates was achieved by pulsed laser deposition using a substrate temperature of 270 °C and a bulk CoSb3 target with 0.75 at.% excess Sb. An InSb (a0 ⳱ 0.6478 nm) substrate was chosen for its lattice registry with the antimonide skutterudites (e.g., CoSb3 with a0 ⳱ 0.9034 nm) on the basis of a presumed 45° rotated relationship with the InSb zinc blende structure. X-ray diffraction and transmission electron microscopy confirmed both the structure of the films and their epitaxial relationship: (001)CoSb3 㛳 (001)InSb; [100]CoSb3 㛳 [110]InSb.
Interest in thermoelectricity has been renewed in recent years due to theories that predict enhanced thermoelectric performance for low-dimensional structures, such as thin-film multilayers.1–7 The materials known as skutterudites (prototype CoAs3 with four formula units in the cubic unit cell) have recently received attention due to their favorable thermoelectric properties and high hole mobilities in bulk single crystal and large-grain polycrystalline forms.8–14 Although there has been some work on growing thin films and multilayers of these materials, no single-crystal films have been reported to date.15–18 Such films with low densities of dislocations and grain boundaries are needed to compare to polycrystalline multilayer structures to fully elucidate the role of artificial structural and compositional modulation on transport properties. This communication reports the deposition parameters and structural characterization of the first epitaxial skutterudite films. The films were grown using pulsed laser deposition (PLD) from a bulk CoSb3 target with excess antimony (0.75 at.%), a substrate temperature of 270 °C, a background argon gas pressure of 10 mtorr, and a target-tosubstrate distance of 6.5 cm. A detailed procedure for producing the PLD targets and a description of the effects of deposition parameters on CoSb3 film stress, composition, and crystallinity have been published.19–21 Before epitaxial growth, the 1-cm2 InSb substrates (Wafer Tech., Ltd., Bucks, UK) were subjected to a native oxide desorption and regrowth treatment. On the basis of a
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Address all correspondence to this author. J. Mater. Res., Vol. 16, No. 9, Sep 2001
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thermal desorption protocol described in the literature,22 the substrate was heated to 400 °C over 15 min in a vacuum base pressure of
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