Examination of proper impurity doping and annealing conditions for solution processed Ga2O3 thin films

Abstract

Abstract We investigated a method to improve the resistivity of Ga2O3 thin films using a wet-process and controlling the Sn-doping conditions. Undoped and Sn-doped single layer Ga2O3 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 Ga2O3 and SnO2 layers in which Sn atoms can diffuse into the Ga2O3 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)2O3 was prepared. By changing the annealing temperature to 800 °C, Al diffusion was suppressed and pure Ga2O3 thin films were prepared. After investigating various conditions of the annealing atmosphere, we found that samples annealed in a nitrogen atmosphere for both Ga2O3 and SnO2 showed the lowest resistivity.