Site localization of Cd impurities in sapphire

G. N. DARRIBA; M. RENTERÍA; H.M. PETRILLI

Atibaia

Workshop; II Workshop do Instituto Nacional de Eletrônica Orgânica - INEO; 2010

Instituto Nacional de Eletrônica Orgânica - INEO

The semiconductor a-Al2O3 (Sapphire) haveimportant technological applications due to its mechanical, thermal, andoptical properties. Some of these applications are related with it use assubstrates, radiation detector crystals, diluted magnetic semiconductors (DMS),etc. For this last use, e.g., the nature of the impurity species in the oxidehost must be well known and understood in order to govern the structural andelectronic properties of the system.Single electric-field gradient (EFG) obtainedfrom γ-γ Perturbed Angular Correlation (PAC) experiments at 111In/111Cdimpurity sites in a-Al2O3 have been alreadyreported in the literature. In these works the hyperfine interaction observedare assigned to Cd probes localized at substitutional cation  sites in the corundum structure.Nevertheless, other authors  claimedthat Cd could be localized at interstitial sites. In this work we present a theoretical studyof  Cd impurities in a-Al2O3 using ab initio calculations for differentimpurity charge states and site localizations (substitutional andinterstitial)  and compare the EFGresults (in magnitude, orientation and symmetry) with the experimental ones.The structural relaxations and electronic properties induced by the presence ofthe Cd impurity in both sites (substitutional and interstitial) in the a-Al2O3 lattice arediscussed too. The ab initio calculations were performed with theFP-APW+lo (Full-Potential Augmented Plane Wave plus Local Orbitals) and PAW(Projector Augmented Wave) methods, both in the framework of the DensityFunctional Theory,  using WIEN2K andCP-PAW codes, respectively. From the comparison between theoryand experiment both substitutional and interstitial scenarios for Cd atoms arepossible. Finally, future possible experiments are discussed that could  resolve these ambiguity.