Hydrogen doping is wide-bandgap amorphous In-Ga-O semiconductors

Microscopic mechanisms of the formation of H defects and their role in passivation of under-coordinated atoms, short- and long-range structural transformations, and the resulting electronic properties of amorphous In-Ga-O with In:Ga=6:4 are investigated using ab-initio molecular dynamics simulations and hybrid density-functional calculations. The results reveal a stark difference between H-passivation in covalent Si-based and ionic oxide semiconductors. Specifically, it is found that hydrogen doping triggers an extended bond reconfiguration and rearrangement in the network of shared polyhedra in the disordered oxide, resulting in energy gains that outweigh passivation of dangling O-p-orbitals. The H-induced structural changes in the coordination and morphology favor a more uniform charge density distribution in the conduction band, in accord with 70-fold increase in carrier mobility measured in H-doped In-Ga-O [1].
A detailed structural analysis helps interpret the observed wide range of infrared frequencies associated with H defects and also demonstrate that bond migration and bond switching behavior within a short picosecond time frame in the disodered oxide governs the stability of OH defects and their diffusion through the lattice.

[1] W. Huang et al, PNAS 117, 18231 (2020)