Ab initio and experimental study of Ta-doped In2O3 semiconductor

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

CAC (CNEA), Buenos Aires , Argentina

Conferencia; "At the Frontiers of Condensed Matter Physics III"; 2006

CAC (CNEA) y Depto. de Física (UBA), Argentina

Ab initio calculations based in the Density Functional Theory have shown to be accurate to describe structural and electronic properties of oxides semiconductors doped with diluted metallic impurities. Therefore these calculations are a powerful tool in the interpretation of experiments in which, e.g., the assignment of hyperfine interactions are rather difficult. In this work we present an ab initio and a new experimental Perturbed Angular Correlation (PAC) study of the In2O3 semiconductor doped with Ta impurities. The theoretical study has suggested in this case a reinterpretation of old experiments and to perform a “cleaner” new experiment. In2O3 pellets with high purity and crystallinity were implanted with 181Hf(®181Ta) ions at the ISKP accelerator of Bonn (Germany) and measured at La Plata with a high time-resolution and efficiency spectrometer. Magnitude and symmetry of the electric-field gradient (EFG) tensor were determined  at room temperature after each step of an annealing series  (1 h at 673K, 1 h at 1073K, 6 hs at 1273K, and 1 h at 1373K). Two monochromatic EFGs were found with the population expected by a homogenous distribution of the probes in both cationic sites C and D of the bixbyite structure (fC/fD=3). These results were compared with those obtained in previous experiments done on samples chemically prepared and on implanted thin films with different initial degrees of crystallinity, in which four interactions were necessary to account for the spectra and the cation site probe population was inverted. Electronic structure calculations were carried out with an impurity dilution of 1:12 using the WIEN97 implementation of the FP-LAPW method. The calculations were carried out for the neutral (Ta0) and charged (Ta2+) state of the impurities, and compared with PCM calculations and the old and new experimental results. From the excellent agreement between the new experiment and the FP-LAPW predictions the neutral state of the impurity could be determined and a correct assignment of the hyperfine interactions in all the experiments were done.