Epitaxial growth and electrical transport properties of Cr 2 GeC thin films
Résumé
Cr2GeC thin films were grown by magnetron sputtering from elemental targets. Phase-pure Cr2GeC was grown directly onto Al2O3(0001) at temperatures of 700–800 °C. These films have an epitaxial component with the well-known epitaxial relationship Cr2GeC(0001)//Al2O3(0001) and Cr2GeC(11¯20)//Al2O3(1¯100) or Cr2GeC(11¯20)//Al2O3(¯12¯10). There is also a large secondary grain population with (10¯13) orientation. Deposition onto Al2O3(0001) with a TiN(111) seed layer and onto MgO(111) yielded growth of globally epitaxial Cr2GeC(0001) with a virtually negligible (10¯13) contribution. In contrast to the films deposited at 700–800 °C, the ones grown at 500–600 °C are polycrystalline Cr2GeC with (10¯10)-dominated orientation; they also exhibit surface segregations of Ge as a consequence of fast Ge diffusion rates along the basal planes. The room-temperature resistivity of our samples is 53–66 μΩcm. Temperature-dependent resistivity measurements from 15–295 K show that electron-phonon coupling is important and likely anisotropic, which emphasizes that the electrical transport properties cannot be understood in terms of ground state electronic structure calculations only.