Archive for the ‘2013’ Category

Posted by Kenneth Burch On October - 5 - 2013 Comments Off on Insulating Ferromagnetic Substrate for Topological Insulators

A ferromagnetic insulating substrate for the epitaxial growth of topological insulators Cr2Ge2Te6 is proposed as an insulating ferromagnetic substrate for the growth of tetradymite-type topological insulators, based on a refined characterization of its transport, magnetic, optical, and calculated electronic properties. It is found to be a soft ferromagnet with no visible magnetic domains over relatively large length scales and to be highly insulating with an indirect band gap and low carrier concentration. Further we present the fabrication of Bi2Te3-Cr2Ge2Te6 heterostructure samples by chemical vapor deposition and show that crystals of the two phases are oriented such that the hexagonal Te planes  [ Read More ]

Posted by Kenneth Burch On May - 30 - 2013 Comments Off on Ferromagnetism and infrared electrodynamics of Ga1-xMnxAs

We report on the magnetic and the electronic properties of the prototype dilute magnetic semiconductor Ga1-xMnxAs using infrared (IR) spectroscopy. Trends in the ferromagnetic transition temperature TC with respect to the IR spectral weight are examined using a sum-rule analysis of IR conductivity spectra. We find nonmonotonic behavior of trends in TC with the spectral weight to effective Mn ratio, which suggest a strong double-exchange component to the FM mechanism, and highlights the important role of impurity states and localization at the Fermi level. Spectroscopic features of the IR conductivity are tracked as they evolve with temperature, doping, annealing, As-antisite compensation, and are found  [ Read More ]

Posted by Kenneth Burch On February - 3 - 2013 Comments Off on Optical properties of SrTiO3 on silicon(100)

Epitaxial buffer layers enable the many functionalities found in perovskites to be integrated with silicon. However, epitaxial growth of SrTiO3 on silicon is tricky and has so far only been achieved by molecular beam epitaxy. Nonetheless, previous investigations of these films were limited by the amorphous layer occurring at the interface. Through a combination of improved interface quality and an improved model, we report the optical properties of SrTiO3 films on Si(100) investigated by spectroscopic ellipsometry. We find that the data are best described by a model with two different SrTiO3 layers, potentially resulting from variations in the oxygen content.  [ Read More ]