Ab initio study of the electronic recombination leading to dynamic Hyperfine interactions observed in 111In(→111Cd)-doped alpha-Al2O3 semiconductor

G. N. DARRIBA; R. VIANDEN; M. RENTERÍA

Nara

Conferencia; International conference on HYPERFINE interactions and their applications; 2023

HFI Executive Committee

The time dependent hyperfine interactions (HFIs) are observed in many (111In→)111Cd-doped binary oxides studied by means of the time-differential perturbed gamma-gamma angular correlations (TDPAC) technique. Experimentally, this effect is characterized by a strong damping in the first ns of the spectra, followed by a constant reduced anisotropy. Usually, the damping increases in a reversible way as the measure temperature decreases, recovering in a full way the anisotropy at high temperature.In a previous work, we studied from an ab initio point of view the electric field gradient tensor (EFG) in Cd-doped α-Al2O3 as a function of the charge state of doped supercells. The results were compared with experimental results on (111In(EC)→)111Cd-doped α-Al2O3 as a function of the measured temperature [1], being able to predict the EFG values of both hyperfine interactions (HFIu and HFId) experimentally observed in the 4-973 K range. The excellent agreement between ab initio predicted and experimentally determined EFGs implies that we could be correctly describing and assigning the observed HFIs. But to be sure that the electronic density configurations represent the experimental situations, a defect formation energy study is necessary.In this work we performed a complete ab initio study of the electronic structure and defect formation energy in Cd-doped α-Al2O3 as a function of the charge state of the doped supercells, using the full-potential augmented plane-wave plus local orbitals (FP-APW+lo) method, implemented in the WIEN2k code. Comparing now the EFG predictions with the experimental results and taking into account the energetic study performed here, we showed that the different final stable electronic configurations reached after the electronic relaxation process generate the observed EFGs. For HFIu we showed that is originated when the acceptor impurity level introduced by the Cd atom is totally filled, and the small decrease of the EFG as T increase is due to thermal lattice effects. On the other hand, for HFId, we showed that small variations of the Fermi level (partially filling the acceptor impurity level introduced by the Cd impurity) generates EFGs that are in agreement with those experimentally observed, corresponding to the different equilibrium charge states reached after the probe-atom electronic relaxation at each measuring temperature.[1] J. Penner and R. Vianden, Hyp. Int. 158, 389 (2004).