Atmospheric pressure chemical vapor deposition of gallium doped zinc oxide thin films from diethyl zinc, water, and triethyl gallium

Abstract

Gallium doped zinc oxide films have been deposited in the temperature range 150 to 470 °C from 0.05% diethyl zinc, 0.8% water, and various triethyl gallium concentrations. The films are polycrystalline with crystallite sizes varying between 275 and 500 Å for undoped films and between 125 and 400 Å for doped films. Only those films deposited above 430 °C are highly oriented and have their c axes perpendicular to the substrate plane. The electron density, conductivity, and mobility always increase with temperature. Thicker films have higher conductivity and mobility than thinner films. The refractive index is reduced from 1.96 to 1.73 when the electron density is increased from zero to 3.7×10²⁰ cm⁻³. For films deposited at 370 °C with a gallium concentration of about 2.5 at. %, the ratio of conductivity to visible absorption coefficient increases from 0.03 to 1.25 Ω⁻¹ when the film thickness increases from 0.11 to 1.2 μm. A film deposited at 470 °C with a gallium concentration of 2.4 at. % and a thickness of 0.66 μm has a sheet resistance of 3.6 Ω/square and an average visible absorption of 6.8%. When the gallium concentration is less than 5.0 at. %, the band gap widening approximately follows the Burstein–Moss relation.