Structural Analysis of Pulsed Laser Deposited FeSi 2 Films
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ABSTRACT This study focuses on the characterization of iron silicide grown, for the first time, by pulsed laser deposition on Si(l 11). Silicide growth was attempted both by deposition of pure Fe followed by annealing, and congruent deposition of Fe and Si from a stoichiometric FeSi2 target. The films formed by deposition of pure Fe and annealing did not grow epitaxially on Si(1 11) and contained a number of phases including 13-FeSi2. Films grown by congruent deposition of Fe and Si did grow epitaxially on Si(1 11) and contained either pure JP-FeSi2 or a mixture of both FeSi and 13-FeSi2, depending on deposition conditions. The following epitaxial orientations were observed: IP-FeSi2(001)//Si(lll), 13-FeSi2[010]//Si with three variants, and FeSi(11l)//Si(111), FeSi[110]//Sit112-]. Films of various thicknesses were analyzed with conventional transmission electron diffraction and microscopy.
I. INTRODUCTION The Fe-Si system has received a great deal of attention due to the existence of a semiconducting phase, P3-FeSi2, with a direct bandgap of 0.87 eV (%=1.42gm) [1,2]. This bandgap corresponds to a wavelength of light in the optimal range for use with fiber optic lines, making 0-FeSi2 an ideal candidate material for fabrication of optoelectronic devices. In addition, P-FeSi2 has an orthorhombic structure (a=9.86A, b=7.79A, c=7.83A) with several planes well matched to and suitable for growth on Si(100) and Si(l 11) surfaces. Previous studies have demonstrated the ability to successfully grow epitaxial P-FeSi2 on Si(100) [3] and Si(1 11) [4-7] using a variety of growth techniques including solid phase epitaxy (SPE) [4,5], molecular beam epitaxy (MBE) [7], liquid phase epitaxy [10] and ion beam synthesis [6]. Currently, the highest quality films have been grown by solid phase epitaxy and molecular beam epitaxy using a template technique [7]. Unfortunately, none of these techniques has yet produced high quality fP-FeSi2 films suitable for fabrication of device structures due to high defect densities and small grain size. This investigation focuses on the growth and characterization of iron silicide films grown on Si(l 11) by pulsed laser deposition. Pulsed laser deposition of iron silicide from stoichiometric FeSi2 targets offers several advantages over other growth techniques. It does not involve multiple step deposition procedures, as in the template technique, nor does it require a large thermal budget in order to affect mass transport over long distances as in SPE. Also, it has been suggested that the stoichiometry of pulsed laser deposited films is identical to that of the ablation target [11]. The high kinetic energy of the incident flux, on the order of tens of eV, might also improve the epitaxial quality of the deposited films by increasing diffusion lengths. 103 Mat. Res. Soc. Symp. Proc. Vol. 320. ©1994 Materials Research Society
1I. EXPERIMENTAL Iron silicide films were grown using a pulsed laser deposition system in a load-locked ultra high vacuum growth chamber with a base pressure of 2x10"10 Torr. High r
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