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

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

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

Ab initio calculations based in the Dens ity Functional Theory have shown to be accurateto describe structural and electronic properties of oxides semiconductors doped withdiluted metallic impurities. Therefore these calculations are a powerful tool in theinterpretation of experiments in which, e.g., the assignment of hyperfine interactions arerather difficult.In this work we present an ab initio and a new experimental Perturbed AngularCorrelation (PAC) study of the In2O3 semiconductor doped with Ta impurities. Thetheoretical study has suggested in this case a reinterpretation of old experiments and toperform a “cleaner” new experiment. In2O3 pellets with high purity and crystallinitywere implanted with 181 Hf(-->181 Ta) 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 atroom temperature after each step of an annealing series (1 h at 673K, 1 h at 1073K, 6hs at 1273K, and 1 h at 1373K). Two monochromatic EFGs were found with thepopulation expected by a homogenous distribution of the probes in both cationic sites Cand D of the bixbyite structure (fC/fD=3). These results were compared with thoseobtained in previous experiments done on samples chemically prepared and onimplanted 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 1:12using the WIEN97 implementation of the FP-LAPW method. The calculations werecarried out for the neutral (Ta 0 ) and charged (Ta 2+ ) state of the impurities, and comparedwith PCM calculations and the old and new experimental results. From the excellentagreement between the new experiment and the FP -LAPW predictions the neutral stateof the impurity could be determined and a correct assignment of the hyperfineinteractions in all the experiments were done.