INSTITUTO DE FISICA LA PLATA
Unidad Ejecutora - UE
congresos y reuniones científicas
PAC experiments and FP-LAPW calculations in doped semiconductors: Ta impurities in Ñ-Al2O3 single crystals
G. N. DARRIBA; E. L. MUÑOZ; M. RENTERÍA; L. A. ERRICO; P. D. EVERSHEIM; H. M. PETRILLI
Rio de Janeiro, Brasil.
Conferencia; 29th International Conference on the Physics of Semiconductors; 2008
The semiconductor a-Al2O3 (sapphire) have important technological applications due to its mechanical, thermal, and optical properties. Some of these applications are related with it use as substrates, crystals for radiation detectors, etc. Impurities in semiconductors play an essential role to develop new properties of these materials and hence it is important to characterize the impurity-host system both from a structural and electronic point of view. A powerful tool for this characterization at the atomic scale is the use of hyperfine techniques combined with ab initio electronic structure calculations. In this work we report a detailed and careful g-g Perturbed-Angular Correlation (PAC) experiments in 181Hf-implanted Al2O3 single crystals in order to maximize the number of probes localized at cation sites, and new ab initio calculations with an impurity dilution 3 times better than those reported in Ref. . The calculations were carry out as a function of the charge state of the impurity, removing up to two electrons, due to the double donor character of the Ta impurity in an Al site in Al2O3. The agreement with the experiment occurs when the probe is partially ionized (0.5 electron removed). The strong EFG dependence on the charge state of the impurity in the calculations is analyzed in terms of the calculated PDOS and the EFG contributions of the different symmetries involved. In addition we studied the structural relaxations predicted by the ab initio calculations in the partially ionized (0.5 electron removed) charge state of the impurity. The Ta impurity introduces large relaxations of the nearest oxygen neighbours (ONN1) and it moves away from the nearest Al neighbours (along the  crystal axis). The ONN1 distance, the shortest one, for this charge state of the impurity try to reconstruct the bond length of Ta in TaO2.  L. A. Errico et al., Phys.Rev.Lett. 89, 55503 (2002).  M. Rentería et al., Phys.Stat.Sol.(b) 242, 1928 (2005).