Structural and electronic properties of Ta-doped sapphire semiconductor: new experiments and

E. L. MUÑOZ, G. N. DARRIBA, L. A. ERRICO, P. D. EVERSHEIM, H. M. PETRILLI, M. RENTERÍA

San Pablo, Brasil

Workshop; 13 Brazilian Workshop on Semiconductor Physics, 1-5 de Abril de 2007, San Pablo, Brasil; 2004

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The semiconductor ®-Al2O3 (zapphire) have important technological applications due to its mechanical, ther-mal, and optical properties. Some of these applications are related with its use as substrates, radiation detectorcrystals, diluted magnetic semiconductors (DMS), etc. In this work new °-° Perturbed Angular Correlation(PAC) experiments in radioactive 181Ta-implanted sapphire single crystals are presented. In previous experi-ments [Phys. Stat. Sol. (b) 242, 1928 (2005)], only one of the two observed hyper¯ne interactions, with a verysmall population, could be assigned to 181Ta probes located at substitutional cation sites, due to the irreversibleprocess generated by a high temperature thermal annealing in air performed to eliminate the radiation damage.In the new one, the sample was carefully annealed at lower temperatures in many steps achieving to locate100 % of the impurities at substitutional cation sites. Two hyper¯ne interactions were observed, one of themassigned to Ta impurities at free of defects cation sites and the other with distant damage. The PAC results arecompared with PCM predictions and ab initio calculations. The ab initio calculations were performed with theFP-LAPW method in the framework of the Density Functional Theory, using WIEN2K code. The PCM cal-culations were performed with and without the structural relaxations predicted by the FP-LAPW calculations.The excellent agreement between the FP-LAPW predictions and the experimental results for the electric-¯eldgradient (in magnitude, orientation and symmetry) enables to determine the structural relaxations introducedby the impurity in the host lattice and the charge state of the impurity level introduced in the band gap of thesemiconductor. This results in a double donor level, which is not ionized at room temperature.