Relationship between electrical properties and crystallization of indium oxide thin films using ex-situ grazing-incidence wide-angle x-ray scattering

Abstract

Grazing-incidence, wide-angle x-ray scattering measurements were conducted on indium oxide thin films grown on silica substrates via pulsed laser deposition. Growth temperatures (TG) in this study ranged from −50 °C to 600 °C, in order to investigate the thermal effects on the film structure and its spatial homogeneity, as well as their relationship to electrical properties. Films grown below room temperature were amorphous, while films prepared at TG = 25 °C and above crystallized in the cubic bixbyite structure, and their crystalline fraction increased with deposition temperature. The electrical conductivity (σ) and electrical mobility (μ) were strongly enhanced at low deposition temperatures. For TG = 25 °C and 50 °C, a strong ⟨100⟩ preferred orientation (texture) occurred, but it decreased as the deposition temperature, and consequential crystallinity, increased. Higher variations in texture coefficients and in lattice parameters were measured at the film surface compared to the interior of the film, indicating strong microstructural gradients. At low crystallinity, the in-plane lattice spacing expanded, while the out-of-plane spacing contracted, and those values merged at TG = 400 °C, where high μ was measured. This directional difference in lattice spacing, or deviatoric strain, was linear as a function of both deposition temperature and the degree of crystallinity. The crystalline sample with TG = 100 °C had the lowest mobility, as well as film diffraction peaks which split into doublets. The deviatoric strains from these doublet peaks differ by a factor of four, supporting the presence of both a microstructure and strain gradient in this film. More isotropic films exhibit larger μ values, indicating that the microstructure directly correlates with electrical properties. These results provide valuable insights that can help to improve the desirable properties of indium oxide, as well as other transparent conducting oxides.

c-Axis Aligned 3 nm Thick In2O3 Crystal Using New Liquid DBADMIn Precursor for Highly Scaled FET Beyond the Mobility–Stability Trade-off

“…Generally, the peak intensity of C(222) for ALD-deposited In 2 O 3 films increases with the deposition temperature because <111> facet is the most stable state with higher atomic density and lower surface free energy than the other facets such as <110> and <100>. , Our group reported that higher deposition temperature of In 2 O 3 for ALD method enhancing the electrical and film properties such as mobility, film density, and surface roughness because (222) dominant films have fewer defect sites and higher atomic density. , However, the C(222) peak intensity of In 2 O 3 deposited above 300 °C decreases, whereas those for other planes such as (046) increase with the deposition temperature increase (Figures c and S4). This result indicates that ALD-deposited In 2 O 3 films also become polycrystalline structures at high deposition temperatures, as reported for the pulsed layer deposition (PLD) and spraying solution method. , …”

“…This result indicates that ALDdeposited In 2 O 3 films also become polycrystalline structures at high deposition temperatures, as reported for the pulsed layer deposition (PLD) and spraying solution method. 39,40 A cross-sectional high-resolution transmission electron microscopy (HRTEM) image and fast-Fourier-transform (FFT) pattern of the In 2 O 3 films near the critical thickness is exhibited in Figure 2. The 250 °C deposited 2 nm thick In 2 O 3 films show an amorphous phase (Figure 2a).…”

Role of the electronically-active amorphous state in low-temperature processed In2O3 thin-film transistors

“…The strongest peak is at 2.22 Å À1 corresponding to the (222) plane of the cubic oxide phase. 34,35 The crystallites are randomly oriented and lack texture. Noticeable diffuse spots in the 2D patterns are the diffuse scattering from the silicon (substrate).…”