We present a dual experimental and computational studies on ruthenium (Ru) induced point defects in wide bandgap semiconductor 4H-silicon carbide (4H-SiC) which is of high interest in alpha, x-ray, and low energy gamma spectroscopy due to Ru’s high weighted metal work function of 4.76 eV which forms a high barrier Schottky contact with low leakage current. We first measured the activation energies and concentrations of deep levels in RF sputtered Ru/n-4H-SiC Schottky diodes annealed at 950°C using deep level transient spectroscopy (DLTS) and identified two deep level defects at Ec – (0.89 ± 0.03) eV and Ec - (1.98 ± 0.03) eV which appear unique to Schottky diodes with Ru. In order to correlate these defects theoretically, we then calculated the formation energies and transition levels of Ru induced point defects in 4H-SiC at charge states [-2, 2] for substitutions and [-2,+4] for interstitials using the projector augmented wave method (PAW) with both PBE and hybrid pseudopotentials on a 3 x 3 x 1 supercell. We found two transition levels which correlate very well with our experimental DLTS results. The transition (-1/0) for Ru substituted into the cubic silicon site at Ev + 2.39 eV and the transition (-1/0) for Ru placed in interstitial site with tetrahedral symmetry to carbon at Ev + 1.23 eV respectively.
We have investigated the electronic structures of bulk GaSe and GaTe as well as the nature of defect states
associated with substitutional impurities and vacancies in GaSe and GaTe. These calculations were done using <i>ab initio</i>
density functional theory and supercell models. We find that the Ga-Ga dimers play an important role in the formation of
defect states. Analysis of the charge densities and the band structures associated with the defect states indicates that they
are strongly localized. Theoretical results are in good agreement with experiment for CdGa and VGa in GaSe and for VGa
in GaTe. The effect of spin-orbit interaction on the band structure of GaTe has been investigated; it is found that the top
valence bands at the Γ-point shift up in energy by ~ 0.1 eV due to the mixing of Te px-py and pz bands.
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