Oxygen annealing induced crystallization and cracking of pulsed laser deposited Ga2O3 films

Amorphous gallium oxide (Ga2O3) films had been prepared on c-sapphire substrate through utilizing pulsed laser deposition at 400 °C and then annealed at various temperatures in an oxygen circumstance. The influence of annealing temperature from 500 to 1000 °C on texture, optical characters, chemical valence state, and surface topography of Ga2O3 films was elaborated systematically. The amorphous film begins to crystallize at 500 °C and the crystallization has been continuously enhanced with the increasing annealing temperature. The optimization annealing temperature is obtained at 700 °C for Ga2O3 thin films with the ratio of 90.4% Ga3+ valence state and 88.6% lattice oxygen which owns a relatively good crystal quality and flat-continuous surface. However, when the temperature goes up to 800 °C and above, some cracks appeared in the film, which could be contributed to the high temperature enhanced Al diffusion into the film as well as the thermal expansion coefficient mismatch between the Ga2O3 films and substrate. The efforts were directed to understand the annealing behavior and thus to derive enhanced ability for manipulation with the specific crystal structure and phase while optimizing the conditions to obtain desirable properties for the integration of Ga2O3 films in electronic device applications.