Electrical Characterization of SiGe Thin Films
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ELECTRICAL CHARACTERIZATION OF SiGe THIN FILMS J. A. MCCORMACK AND J.-P. FLEURIAL Jet Propulsion Laboratory/California 4800 Oak Grove Dr., Pasadena, CA 91109
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ABSTRACT and Hall An apparatus for measuring electrical resistivity over a coefficient on both thin films and bulk material temperature range of 300K to 1300K has been built. A unique alumina fixture, with four molybdenum probes, allows arbitrarily shaped samples, up to 2.5 cm diameter, to be measured using van and is fully automated system is The der Pauw's method. Measurements constructed with commercially available components. of the electrical properties of doped and undoped Si-Ge thin films, grown by liquid phase epitaxy reported here, are to the capabilities of the apparatus. illustrate
INTRODUCTION thermoelectric of the high temperature Improvement conversion efficiency of hot-pressed n-type Si-Ge alloys required that substantial increase in the carrier concentration of these Because of the limited solid solubility materials be made [1]. of the dopants used, combinations of several elements such as Ga However, the understanding of the and P have been used [2,3]. doping mechanisms in the hot-pressed materials is quite complex To better are difficult to reproduce. and the results investigate the behavior of these alloys, characterization of For this homogeneous single crystalline materials are needed. growth of high quality Si-Ge thin films doped with purpose, various elements has been carried out using liquid phase epitaxy (LPE), a near-thermodynamic equilibrium process [4]. Characterizing these thermoelectric materials also involved using a Hall measuring their electrical transport properties, effect apparatus. Because of the significant effects of dopant precipitation on the properties and of the high temperature range measurements needed to be conducted from room of interest, temperature up to 1000 OC. Hall resistivity and common method for measuring A This based on van der Pauw's technique [5]. coefficient is arbitrarily shaped discs to be tested, technique allows for flat
Mat. Res. Soc. Symp. Proc. Vol. 234. ©1991 Materials Research Society
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provided that the electrical contacts are sufficiently small and located along the circumference of the sample, and the sample is free of (geometrical) holes. From these measurements, the following properties can be obtained: electrical resistivity, Hall coefficient, Hall mobility, and Hall concentration. Due to the high temperature range of applications of the Si-Ge thermoelectric alloys, the fixture design, its implementation, and the measuring process presented a variety of problems over standard room temperature measurements such as choice of materials, electrical connections, measurement and temperature control. The system is built with commercially available equipment and is fully automated with an AT compatible computer, via an IEEE-488 interface. The software is written in Microsoft's Quick Basic 4.5 for its fast prototyping capabilities and ease of use.
APPARATUS DES
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