Stabilizing the metastable γ phase in Ga2O3 thin films by Cu doping

Abstract The metastable cubic γ phase Ga 2 O 3 with a defect spinel structure presents several fascinating properties, which may be a more attractive material than the stable β form. Herein, we found that the metastable γ -Ga 2 O 3 can be stabilized by copper (Cu) doping through a simple operation and low cost method of sol-gel. The γ -Ga 2 O 3 thin films were prepared under the annealing of 700 °C in nitrogen atmosphere for Cu doping. The β phase Ga 2 O 3 ones were obtained at the same condition without the Cu dopant. While the Cu doped γ phase Ga 2 O 3 will transform to β phase for a high annealing temperature above 800 °C. The grain size of Cu doped γ -Ga 2 O 3 and undoped β -Ga 2 O 3 thin films increases with the increase of the annealing temperature. The UV–Vis absorption spectrum of the β -Ga 2 O 3 thin film exhibits a sharp intrinsic absorption edge at ∼250 nm, whilst Cu doped γ -Ga 2 O 3 thin film displays an obvious red-shift. The band gap decreases from 4.90 eV to 4.38 eV for the Cu doping. The photoluminescence intensity at the ultraviolet and blue region of Cu doped γ- Ga 2 O 3 thin films are stronger than undoped β -Ga 2 O 3 , which can be attributed to the introduction of more defects such as oxygen vacancies in γ phase by Cu doping.