Atomic and electronic structure of crystalline InGaO3(ZnO)m

Woo-Jin Lee, Eun-Ae Choi, Junhyuk Bang, Byungki Ryu, and Kee Joo Chang

Department of Physics,Korea Advanced Institute of Science and Technology,

Daejeon 305-701,Korea

InGaO3(ZnO)m belongs to the homologous oxides and is composed of an alternating stack of an InO2 layer and a GaO(ZnO)m block. Due to the layered structure, the quantum effect such as the spatial confinement of charge carriers is expected in this material. Recently, InGaO3(ZnO)m has attracted much attention because of the potential applications for transparent and optoelectronic devices. The key issues are the structural models for the distribution of the Ga and Zn atoms in a GaO(ZnO)m block and the electronic structure related to the quantum confinement in the layered structure.

In this work we investigate the atomic and electronic structure of InGaO3(ZnO)m through the first-principles calculations within the density functional theory framework [1]. We consider two configurations for the distribution of the Ga atoms, such as a flat boundary structure and a modulated boundary structure. In the flat boundary model, where the Ga atoms are located in a single layer, the stacking sequence of the ZnO layers is inverted with respect to the GaO layer, resulting in the cancellation of the polarities of the ZnO layers and a good connection between the InO2 layer and neighboring ZnO layers. On the other hand, in the modulated boundary structure, the Ga atoms form a zigzag boundary and induce a similar inversion of the stacking sequence of the ZnO layers. Due to tensile strains loaded in the ZnO layers, the flat boundary structure is less stable than the modulated boundary structure. In both structural models, we find that hole carriers are spatially confined to specific regions of the ZnO layers whereas no clear confinement occurs for electron carriers. As the confinement of hole carriers is enhanced in the modulated boundary structure, the band gaps are slightly larger than those for the flat boundary structure.

[1] W.-J. Lee, E.-A. Choi, J. Bang, B. Ryu, and K. J. Chang, Appl. Phys. Lett., in press (2008).