Structural and electronic properties of Ta-doped sapphire semiconductor: New experiments and ab initio calculations

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

San Pablo, Brasil

Workshop; Brasilian Workshop on Semiconductor Physics; 2007

The semiconductor a-Al2O3 have important technological applications due to its mechanical, thermal and optical properties. Some of these applications are in substrates, radiation detector crystals, diluted magnetic semiconductors (DMS), etc. In this work new PAC experiments in Ta-doped sapphire are presented. In this experiment, the sample was thermally annealed without irreversibly damage, where the 100 % of the impurities are located in substitutional cation sites. Two hyperfine interactions were assigned to localize these impurities in substitutional cation sites, one of them free of defects and the other with a remaining damage. In the old experiment, an only hyperfine interaction was assigned to Ta probes in substitutional cation sites, but with very small population, due to the irreversible damage generated by the thermal annealing. The PAC experiments were compared with PCM predictions and ab initio calculations. The ab initio calculations were performed with the FP-LAPW method in the framework of the Density Functional Theory, using WIEN2K code. The PCM calculations were performed with and without structural relaxations predicted by FP-LAPW calculations. The FP-LAPW predictions and the experimental results of the magnitude, orientation and symmetry of the Electric Field Gradient are in excellent agreement. This theoretical-experimental approach permitted to determine the structural relaxations produced by the inclusion of the impurity in the host lattice, and the state of charge of the impurity level in the prohibited band of the semiconductor.  The impurity introduces a double donor level in the gap of the semiconductor, which is not ionized at room temperature.