Mechanism of electrical conductivity of transparent InGaZnO4

The electronic structure of InCaZnO4, which has a layered structure with alternating laminated layers of InO2 and GaZnO2, was calculated in order to investigate the mechanism of electrical conductivity. In the crystal structure obtained through relaxation calculations using classical two-center potentials, the Ga ion in the GaZnO2 layer has pentagonal coordination forming a bipyramid with five oxygen ions, while the Zn ion in the same layer has tetrahedral coordination, losing a bond with the oxygen at the top of one pyramid. The molecular orbitals of model clusters for the relaxed structure, which were calculated by the discrete variational Xa method using a model cluster, show strong two-dimensional structures. The electronic states at the edge of the conduction band are the result of overlapping between In 5s orbitals, and delocalize in the InO2 layer. The energy in the Ga 4s and Zn 4s states in the GaZnO2 layer was too large to be doped with electrons. The In 5s states are considered to be conduction paths for carrier electrons. A very high conductivity can be expected in the case where dopant ions are introduced into the GaZnO2 layers.