First-principles study on the geometry and electronic structures of IIIA atoms doped α-[Al.sub.2][O.sub.3]:[V.sub.O]

We investigate the geometry and electronic structures of α-[Al.sub.2][O.sub.3]:[V.sub.O] + [Al.sub.X] systems based on first-principles calculations where [V.sub.O] represents one oxygen vacancy and [Al.sub.x] stands for IIIA atoms (B, Ga, In, and Tl) substituting of one Al atom. It is found that all the aluminates maintain the hexagonal symmetry as the pure α-[Al.sub.2][O.sub.3] structure and the lattice parameters a, b, and c are expanded with the increase of the IIIA atoms radius. The electronic property analysis indicates that the band gaps are considerably reduced and the reductions are also related to the radius of doping atoms. But unlike the situation of transition metal doped α-[Al.sub.2][O.sub.3] the decreases of the band gap are not due to the spreading of d states, but are mainly owing to the ns states at the bottom of the conduction band. PACS No.: 71.20.Nr. Nous etudions la geometrie et les structures electroniques de systemes α-[Al.sub.2][O.sub.3]:[V.sub.O] + [Al.sub.X], a partir de calculs ab initio, ou [V.sub.O] presente une lacune d'un atome d'oxygene et [Al.sub.x] signifie qu'un atome de Al est remplace par un atome substitut de type IIIA (B, Ga, In et Ti). Nous trouvons que tous les aluminates conservent la symetrie hexagonale comme la structure de α-[Al.sub.2][O.sub.3] pur et que les parametres du reseau, a, b et c, augmentent avec le rayon de l'atome IIIA. L'analyse des proprietes electroniques indique que la bande interdite est considerablement reduite et que ces reductions sont aussi reliees au rayon de l'atome dopant. Contrairement au dopage de α-[Al.sub.2][O.sub.3] par metal de transition, la diminution de la bande interdite n'est pas due a l'etalement des etats d, mais est due surtout au maintien des etats ns au fond de la bande de conduction. [Traduit par la Redaction]
1. Introduction The sapphire phase of alumina (α-[Al.sub.2][O.sub.3]), which has a broad bandgap (8.7 eV), is widely used in optical devices. In the past two decades, a large amount of [...]