Growth and properties of thin film semiconducting iron disilicide produced by pulsed laser deposition.

Investigation of the properties of $\beta$-FeSi$\sb2$ for evaluation of possible applications in the automotive industry has been performed. Before $\beta$-FeSi$\sb2$ can be utilized many fundamental questions concerning growth techniques and resulting electrical and optical properties need to be addressed. This work presents relationships between changes in the optical, electrical, and magnetic properties with differences in film microstructure brought about by small variations in growth conditions. Since each of the many growth techniques employed thus far have particular advantages as well as inherent drawbacks, the use of new growth techniques and their subsequent evaluation are important steps toward the implementation of $\beta$-FeSi$\sb2$ as a useful engineering material. We employed pulsed laser deposition to produce thin films of $\beta$-FeSi$\sb2$ on silicon (111) surfaces. The success of this technique is primarily due to congruent evaporation which preserves the stoichiometry of multicomponent targets. Using transmission electron diffraction we report that this technique produces polycrystalline epitaxial films with the smallest geometric misfit known for this material system. Results of optical transmission measurements and calculations reveal the existence of high defect densities that produce band tails with an apparent energy width greater than the measured difference between the indirect and direct transition energy levels. Results show that the defect density is influenced by growth induced variations in the microstructure. This evidence suggests that a high defect density precludes a correct assignment of the intrinsic value as well as of the nature of the energy gap. We also report that additional insight into the nature of the defects and their influence on the film properties is achieved through examination of the magnetization. The temperature dependence of the resistivity is consistent with Mott type variable range hopping conduction for a 3D disordered system. Calculations of the localization length, the optimum hopping distance, and the critical saturation field have produce reasonable values considering the physics of hopping conduction and the sample geometry. We have found that magnetoresistance follows a low-field dependence proportional to H$\sp2$ while the high-field dependence is proportional to H$\sp{1/2}.$ The onset of negative magnetoresistance for all samples occurs at $\sim$20K despite differences in microstructure, and defect density.PhDApplied SciencesCondensed matter physicsMaterials sciencePure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/129720/2/9610213.pd