We examine ZnSnN2, a member of the class of materials contemporarily termed “earth-abundant element semiconductors,” with an emphasis on evaluating its suitability for photovoltaic applications. It is predicted to crystallize in an orthorhombic lattice with an energy gap of 2 eV. Instead, using molecular beam epitaxy to deposit high-purity, single crystal as well as highly textured polycrystalline thin films, only a monoclinic structure is observed experimentally. Far from being detrimental, we demonstrate that the cation sublattice disorder which inhibits the orthorhombic lattice has a profound effect on the energy gap, obviating the need for alloying to match the solar spectrum.

Thin films of SnO 2 prepared by pulsed-laser deposition on R-cut sapphire substrates exhibit ferromagnetic properties at room temperature when they are doped with Cr, Mn, Fe, Co, or Ni, but not with other 3d cations. Extrapolated Curie temperatures are generally in excess of 500 K. The moment of the films is roughly independent of doping level, from 0.1-15 at. %, with a value per unit substrate area of 200± 100 B nm −2 . When magnetization is expressed as a moment per 3d dopant ion, it varies from more than the spin-only value at low concentrations to less than 0.2 B /ion near the percolation threshold. Greatest values are found for iron. The magnetization of the films is highly anisotropic with values when the field is applied perpendicular to the substrate more than double the in-plane values. There is little hysteresis except at high doping levels. The oxides are degenerate n-type semiconductors with a Hall mobility of 100 cm 2 V −1 s −1 and 1.4ϫ 10 19 carriers cm −3 in a one-band model, but no anomalous Hall effect or magnetoresistance was observed at room temperature. The data are discussed in relation to ͑a͒ the donor impurity-band model of ferromagnetism in semiconductors and ͑b͒ the magnetic defect model.

The phase diagram of FeSi(1-x)Ge(x), obtained from magnetic, thermal, and transport measurements on single crystals, shows a discontinuous transition from Kondo insulator to ferromagnetic metal with x at a critical concentration, x(c) approximately 0.25. The gap of the insulating phase strongly decreases with x. The specific heat gamma coefficient appears to track the density of states of a Kondo insulator. The phase diagram is consistent with an insulator-metal transition induced by a reduction of the hybridization with x in conjunction with disorder on the Si/Ge ligand site.

No abstract

We report a detailed study of the morphology of TiO2:Co films grown on both LaAlO3 (001) and SrTiO3 (001) substrates by pulsed laser deposition. The films are optically transparent and ferromagnetic at room temperature with a magnetic moment of 1.7±0.4 μB/Co. Plan view transmission electron microscope studies show clear evidence of cobalt segregation with the clustering more pronounced for higher cobalt concentrations. Films grown on SrTiO3 substrates show the presence of a thin surface rutile (111) layer, into which the cobalt appears to migrate. These results are supported by x-ray structure determination and resistivity measurements.