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

The metastable cubic gamma phase Ga2O3 with a defect spinel structure presents several fascinating properties, which may be a more attractive material than the stable beta form. Herein, we found that the metastable gamma-Ga2O3 can be stabilized by copper (Cu) doping through a simple operation and low cost method of sol-gel. The gamma-Ga2O3 thin films were prepared under the annealing of 700 degrees C in nitrogen atmosphere for Cu doping. The beta phase Ga2O3 ones were obtained at the same condition without the Cu dopant. While the Cu doped gamma phase Ga2O3 will transform to beta phase for a high annealing temperature above 800 degrees C. The grain size of Cu doped gamma-Ga2O3 and undoped beta-Ga2O3 thin films increases with the increase of the annealing temperature. The UV-Vis absorption spectrum of the beta-Ga2O3 thin film exhibits a sharp intrinsic absorption edge at similar to 250 nm, whilst Cu doped gamma-Ga2O3 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 gamma-Ga2O3 thin films are stronger than undoped beta-Ga2O3, which can be attributed to the introduction of more defects such as oxygen vacancies in gamma phase by Cu doping. (C) 2017 Elsevier B.V. All rights reserved.