Metal-organic chemical vapor deposition of Zn-In-Sn-O and Ga-In-Sn-O transparent conducting oxide thin films

The metal-organic chemical vapor deposition (MOCVD) technique has been successfully applied for growth of Sn-doped transparent, conducting Zn-In-O and Ga-In-O films using Sn(acac)₂, In(dpm)₃, Ga(dpm)₃, and Zn(dpm)₂, as volatile precursors. The 25 °C electrical conductivity of the as-grown films is as high as 1030 S/cm (n-type, carrier density N = 4.5×10²⁰ cm^-3, mobility μ = 14.3 cm²/V·s) for the Zn-In-O series and 700 S/cm (n-type, N = 8.1×10¹⁹ cm^-3, μ = 55.2 cm²/V·s) for the Ga-In-O series. After Sn-doping, the Zn-In-O series exhibits 25 °C electrical conductivities as high as 2290 S/cm with a higher carrier mobility, while the Ga-In-O series exhibits higher electrical conductivity (3280 S/cm at 25 °C) and much higher carrier density, but with diminished mobility. All films show broader optical transparency windows than that of commercial ITO films. Reductive annealing, carried out at 400-425 °C in a flowing gas mixture of H₂ (4%) and N₂, results in increased carrier density and mobility as high as 64.6 cm²/V·s for films without Sn doping, but lowered carrier density for the Sn-doped films. X-ray diffraction, transmission electron microscopy, micro diffraction, and high-resolution X-ray analysis show that all films with good conductivity have cubic, homogeneously doped In₂O₃-like crystal structures.