A photoluminescence comparison of CdTe thin films grown by molecularbeam epitaxy, metalorganic chemical vapor deposition, and sputtering in ultrahigh vacuum Photoluminescence spectra are measured for sputter-deposited, heteroepitaxial (lOO)CdTe layers of thicknesses up to 14,um grown on (lOO)KBr substrates. Three emission bands, at 0.81, 1.00, and 1.41 eV, are observed. From comparison of the photoluminescence spectra of the epilayers with those of several bulk single-crystal and polycrystalline samples, the origin of the 1.41-eV band, reported previously by many workers, is correlated to structural defects arising from lattice mismatch with the substrate. It is concluded that the 0.81-and l.OO-eV bands are due to defect levels resulting from nonstoichiometric growth. The injection level and temperature dependence of the photoluminescence suggest that the 1.41-and O.81-eV emissions are donor-acceptor transitions whereas the LOO-eV emission is a conduction-band-acceptor transition.
The microstructural and optical properties of tungsten thin films prepared by dc magnetron sputtering were investigated as a function of the argon pressure. The films were characterized by x-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), x-ray diffraction (XRD), grazing x-ray reflectometry (GXR), and spectroscopic ellipsometry (SE). From the analysis of the XPS data, the films were found to consist of a base tungsten layer, a graded oxide transition layer, and a surface oxide layer. Also, the thickness of the oxide layers were determined. XRD indicated that the films were either amorphous or composed of crystallites with grain size <100 Å. STM and GXR have revealed that the films grown at low pressures were the smoothest. Finally, SE measurements allowed the determination of the dielectric function of a compact tungsten layer. Further SE analysis of the films indicated that with increasing argon pressure, the films developed into a more voided columnar structure.
An rf magnetron discharge used to sputter PbTe in Ar is analyzed using emission spectroscopy. The intensity (I) of the strong Pb, Te, and Ar emission lines is determined near the target and near the substrate as the rf power or gas pressure is varied. It is shown that as the rf power is varied at pressures below 0.5 Pa, the electron temperature is not affected, so that the sputtered atom density NPb is proportional to IPb/IAr. The electron temperature is, however, sensitive to pressure changes. Application of a substrate bias voltage has a large effect on the emission spectra which are not understood.
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