Effects of Diffusion of Hydrogen and Oxygen on Electrical Properties of Amorphous Oxide Semiconductor, In-Ga-Zn-O

We found that device-quality thin films of amorphous oxide semiconductor, a-In-Ga-Zn-O, unintentionally include high-density hydrogens over 1020 cm−3 but the electron concentration remains low at ∼1015 cm−3 in as-deposited states. The hydrogens exist in the form of hydroxyl group –OH, but most of them are inactive as an electron donor, which is explained by charge compensation due to incorporation of excess oxygens. Although their diffusions are fast compared with those in crystalline ZnO, but oxygen can diffuse only 20 nm even at 400°C. Hydrogen diffusion is much faster, and easily hydrogenizes a thin channel of a thin-film transistor.