State and Role of Hydrogen in Amorphous Oxide Semiconductors

Hydrogen is an unavoidable impurity species in oxide semiconductor thin films. The concentration of H-impurity in conventional sputtering-deposited AOS (amorphous oxide semiconductor) thin films goes up to 10 20 –10 21 cm −3 . These hydrogen species are incorporated during vacuum deposition processes through reactions with residual gas species, H 2 O and H 2 , in the vacuum chamber. This chapter describes the current understanding of hydrogen-related impurities and defects in AOS materials, focusing on their chemical states, energy levels, and influence on carrier generation and annihilation.