Carbon as a Shallow Donor in Transparent Conducting Oxides

Carbon is a common unintentional impurity in oxide semiconductors. We use hybrid density functional theory to calculate the electronic and structural properties of carbon impurities in ZnO, In2O3, and Ga2O3-materials that are used as transparent conductors. In each of these semiconducting oxides, we find that carbon is most likely to occupy the cation site under most electronic and chemical potential conditions. In ZnO, CZn acts as a shallow double donor and exhibits large local breathing-mode relaxations. In In2O3 and Ga2O3, C acts as a shallow donor and moves off the cation site to become threefold oxygen coordinated. In all three oxides, Ccation exhibits modest formation energies, indicating that these species will be likely to incorporate. Our results indicate that C impurities are suitable donor dopants in these oxides and will contribute to background n-type conductivity if unintentionally present.