Structural analysis of Cd–Te–O films prepared by RF reactive sputtering

Crystalline and microcrystalline Cd–Te–O samples have been obtained by RF reactive sputtering from a CdTe target using N ₂ O as oxidant. The growth conditions were substrate temperatures of 323 K, 573 K and 773 K and cathode voltage of −400 V, corresponding to 30 W of forward power. The samples were studied by micro-Raman spectroscopy, X-ray diffraction and optical transmittance. The films are remarkably transparent in the visible range, with transmittances about 88% at 400 nm and band gap energies above the absorption edge of the glass substrates. Although only the samples prepared at 773 K present defined diffraction peaks, the analysis of the Raman spectra indicate that samples prepared at 323 K and 573 K have a defined microstructure indeed. The spectra fitting performed by comparison with pattern compounds demonstrate that Cd–Te–O films are formed of Te–O units similar to those present in metal oxide-doped tellurite glasses, such as TeO ₃ and TeO _{3 + 1} linked through Cd–O bonds. As the substrate temperature increases the microstructure evolves from a γ-TeO ₂ richer state to Cd _xTe _yO _z. In the crystalline sample the main phase identified was CdTeO ₃ even though evidence of other phases was observed.