Microstructure and Electrical Properties of PbTe Based Films Prepared by Pulsed Laser Deposition
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Microstructure and Electrical Properties of PbTe Based Films Prepared by Pulsed Laser Deposition Anne Dauscher, Bertrand Lenoir, Alexandre Jacquot, Christine Bellouard and Maria Dinescu1 Laboratoire de Physique des Matériaux, UMR 7556, Ecole des Mines, Parc de Saurupt, F-54042 Nancy, France. 1 NILRP, Laser Department, P.O. Box MG-16, RO-76900 Bucharest, Romania. ABSTRACT Lead telluride thin films have been grown on BaF2(111) substrates by pulsed laser deposition from a Nd:YAG laser (λ = 532 nm) at very low temperature (150°C). The chemical composition, the morphology and the crystallographic structure of the layers depend strongly on the deposition conditions. Post-annealing treatments of the films also affect their microstructure. Preliminary electrical properties, conducted in the temperature range of 5 to 350 K, revealed that all the samples were n-type with Hall mobility values greater than 104 cm2/V.s at low temperatures.
INTRODUCTION Heterostructures and superlattices of AIVBVI materials have attracted considerable interest for both their structural and fundamental electronic properties. Lead telluride (PbTe) is well known as a narrow-gap semiconductor, sensitive in the mid and far infrared spectral region, that has been applied mainly in the fabrication of photodetectors and diode lasers [1]. Its good thermoelectric properties in the bulk form, associated with the ease to produce a compatible barrier material, made it also a good candidate to test the possibilities of enhancing the thermoelectric performances in quantum confined systems. In-plane thermoelectric figures of merit ZT exceeding unity were reported in high carrier concentration n or p-type PbTe quantum wells [2,3]. Evidence for a strong reduction of the in-plane thermal conductivity leading to enhanced thermoelectric performances has also been demonstrated in lead salt-based multilayered structures [4]. Epitaxial growth of PbTe based films or heterostructures has generally been performed by molecular beam epitaxy (MBE) or hot wall epitaxy (HWE) on BaF2(111) substrates at temperatures higher than 300°C. The purpose of our work was to prepare PbTe thin films deposited on BaF2(111) substrates by pulsed laser deposition (PLD) and to study the influence of the deposition parameters on the microstructures of the layers. Preliminary results concerning the temperature dependences of the Hall mobility and carrier concentration are also reported. PLD is a simple preparation technique allowing the deposit of virtually any material, from pure elements to multi-component compounds, while keeping the stoichiometry of the target material [5]. High quality films are generally achieved at lower deposition temperature than with any other deposition technique and that is particularly interesting for the preparation of multi-layers to limit the problems associated to inter-diffusion.
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EXPERIMENTAL DETAILS Thin film deposition was carried out under vacuum in a stainless steel chamber already described [6] allowing a base pressure of 10-7 mbar during depositi
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