Hydrogen-doped In2O3 transparent conducting oxide films prepared by solid-phase crystallization method

We have characterized amorphous to crystalline transformation of hydrogen (H)-doped In2O3 (In2O3:H) films by transmission electron microscopy, thermal desorption spectroscopy, spectroscopic ellipsometry, and Hall measurements. The In2O3:H films that show a mixed-phase structure embedded with small density of crystalline grains in a large volume fraction of amorphous phase have been fabricated at room temperature by the sputtering of an In2O3 ceramic target with introduction of H2O vapor, and the films have been postannealed in vacuum to crystallize the amorphous phase. With increasing annealing temperature up to 200 °C, the film shows a large increase in Hall mobility (μHall) from 42 to 110 cm2/V s and a decrease in carrier density (NHall) from 4.6×1020 to 2.1×1020 cm−3 with slight decrease in resistivity. The change in μHall and NHall with annealing temperature is strongly correlated with the volume fractions of the amorphous and crystalline phases in the films. Analyses of dielectric functions of the films using the Drude model revealed that the high electron mobility in the crystallized films is attributed mainly to longer relaxation time rather than smaller effective mass, as compared with as-deposited films. Temperature-dependent Hall analysis, relationship between NHall and μHall, and comparison between μHall and optical mobility showed that (i) scattering processes inside amorphous and/or crystalline matrices limit the mobility, (ii) doubly charged ionized impurity scattering is reduced by crystallization, and (iii) phonon scattering becomes dominant after crystallization in the In2O3:H films. The above results suggest that H-doping reduces carrier scattering in the crystallized In2O3:H and structural rearrangements during crystallization eliminate oxygen deficiency and generate H+ that acts as a singly charged donor. In this article, we discuss the transport properties with the variation in microscopic and chemical structures in the In2O3:H films.