Defect Passivation and Carrier Reduction Mechanisms in Hydrogen-Doped In-Ga-Zn-O (IGZO:H) Films upon Low-Temperature Annealing for Flexible Device Applications

Low-temperature activation of oxide semiconductor materials such as In-Ga-Zn-O (IGZO) is a key approach for their utilization in flexible devices. We previously reported that the activation temperature can be reduced to 150 degrees C by hydrogen-doped IGZO (IGZO:H), demonstrating a strong potential of this approach. In this paper, we investigated the mechanism for reducing the activation temperature of the IGZO:H films. In situ Hall measurements revealed that oxygen diffusion from annealing ambient into the conventional Ar/O-2-sputtered IGZO film was observed at >240 degrees C. Moreover, the temperature at which the oxygen diffusion starts into the film significantly decreased to 100 degrees C for the IGZO:H film deposited at hydrogen gas flow ratio (R[H-2]) of 8%. Hard X-ray photoelectron spectroscopy indicated that the near Fermi level (E-F) defects in the IGZO:H film after the 150 degrees C annealing decreased in comparison to that in the conventional IGZO film after 300 degrees C annealing. The oxygen diffusion into the film during annealing plays an important role for reducing oxygen vacancies and subgap states especially for near E-F. X-ray reflectometry analysis revealed that the film density of the IGZO:H decreased with an increase in R[H-2] which would be the possible cause for facilitating the O diffusion at low temperature.

Automated summary

The mechanism for reducing the activation temperature of IGZO:H films was investigated in this paper. In situ Hall measurements and hard X-ray photoelectron spectroscopy analysis revealed that oxygen diffusion during annealing played an important role in reducing oxygen vacancies and subgap states near the Fermi level. Additionally, X-ray reflectometry analysis showed that the density of the IGZO:H film decreased with increasing hydrogen gas flow ratio.