Structural and electronic properties of dilute oxide semiconductors: experimental and ab initio study of Ta-doped Al2O3 single crystals

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

La Plata

Workshop; HFILP2005, International Workshop “35th Anniversary of Hyperfine Interactions at La Plata"; 2005

Laboratorio de Espectroscopía Nuclear e Interacciones Hiperfinas, FCE, UNLP e IFLP (CONICET)

In the last 3 years, electronic structure ab initio methods in the framework of theDensity Functional Theory (DFT) have been intensively applied to describe interestingproperties in nonmagnetic [1] and magnetic [2] dilute impurities in oxide semiconductors, the last appealing for spintronics [3]. The Full-Potential Linearized-AugmentedPlane Waves (FP -LAPW) method, focusing at the ele ctric -field gradienttensor (EFG) in doped systems, was first applied succesfully to the (N,P,As,Sb)-dopedCdTe semiconductor [4] and at an impurity site in Cd-doped TiO2 oxide [5]. Being theelectric-field gradient (EFG) a magnitude strongly dependent of the asphericity of theelectronic density near the probe-nucleus, its determination enables to check theapproximations made beyond the DFT and to study interesting electronic and structuralproperties in these systems [5].In this work we report Perturbed-Angular-Correlation (PAC) experiments on181 Hf/181 Ta-implanted corundum alpha-Al2O3 single crystals. The magnitude, asymmetry,and orientation (with respect to the crystalline axes) of the EFG were determinedmeasuring the spin-rotation curves as a function of different orientations of the singlecrystals relative to the laboratory system. The experiments were carried out as afunction of temperature and of diverse thermal treatments, giving rise to two hypefineinteractions instead of the single interaction expected for probe atoms localized atdefect-free Al sites. These results are analyzed in terms of self-consistent electronicstructure FP -LAPW calculations in the dilute (1:4) Al2O3:Ta system and compared withEFG results coming from PAC exper iments using 111 In/111 Cd tracers and for bothprobes ( 181 Ta and 111 Cd) in isomorphous polycrystalline alpha-Fe2O3. This combined studyenables the determination of lattice relaxations induced by the presence of the impurityand its displacement in the [001] axis and of the charge state of a deep impurity donorlevel (Ta 5d) located in the band gap of the semiconductor.[1] C.Verdozzi et al., Phys.Rev.Lett. 80, 5615 (1998); A. Settels et al., Phys.Rev.Lett.83, 4369 (1999); C. Stampfl et al., Phys.Rev. B 61, R7846 (2000).[2] M. S. Park et al. , Phys.Rev. B 65, 161201 (2002); Z. Yang et al. , Phys.Rev. B 67,060402(R) (2003); W. T. Geng and K. S. Kim, Phys.Rev. B 68, 125203 (2003; L.A.Errico, M. Rentería, and M. Weissmann, Phys.Rev. B, (2005), in press.[3] H. Ohno, Science 281, 951 (1998); T. Dietl et al. , Science 287, 1019 (2000).[4] S. Lany, P. Blaha, J. Hamann, V. Ostheimer, H. Wolf, and T. Wichert, Phys.Rev. B62, R2259 (2000).[5] L.A. Errico, G. Fabricius, M. Rentería, P. de la Presa, and M. Forker, Phys.Rev.Lett.89, 55503 (2002); L.A. Errico, G. Fabricius, and M. Rentería, Phys.Rev. B 67, 144104(2003).Keywords: Al2O3, single crystal, FP-LAPW, PAC, 181 Hf, 181 Ta, 111 In, 111 Cd, impuritydonor level, oxide