Examination of proper impurity doping and annealing conditions for solution processed Ga 2 O 3 thin films

We investigated a method to improve the resistivity of Ga 2 O 3 thin films using a wet-process and controlling the Sn-doping conditions. Undoped and Sn-doped single layer Ga 2 O 3 thin films were prepared by changing the solution concentration, the annealing time, the rate of temperature rise, and the speed of the sample rotation in spin coating during deposition. As a result, the films were deposited uniformly with good crystallinity and transmittance and relatively small surface roughness. To improve the resistivity by another Sn-doping method, we prepared bilayer samples consisting of undoped Ga 2 O 3 and SnO 2 layers in which Sn atoms can diffuse into the Ga 2 O 3 layer through annealing, i.e. the drive-in diffusion method. Although the changed resistivity, X-ray electron spectroscopy (XPS) and transmission electron microscope, energy dispersion X-ray spectroscopy measurements revealed that Al diffused from the sapphire substrate, indicating a mixed β -(Ga,Al) 2 O 3 was prepared. By changing the annealing temperature to 800 °C, Al diffusion was suppressed and pure Ga 2 O 3 thin films were prepared. After investigating various conditions of the annealing atmosphere, we found that samples annealed in a nitrogen atmosphere for both Ga 2 O 3 and SnO 2 showed the lowest resistivity.