High performance solar blind photodetector based on β-Ga2O3 achieved via face-to-face thermal annealing with oxygen plasma treatment

• Novel processing technique: Combining high active oxygen plasma with thermodynamic regulation, the surface roughness is reduced to 1/2 of the initial value by face-to-face annealing process. • Detailed Microscopic Analysis: Double regulation of surface and internal defects. The surface and internal oxygen vacancies are reduced to 2.88 % and 2.53 %, respectively. • Stable and excellent performance: The optimized photocurrent-to-dark current ratio is as high as 6.06 × 10⁷, and the detectivity is 5.68 × 10¹⁵ Jones. We have achieved significantly improved device performance in solar-blind photodetectors fabricated from β -Ga 2 O 3 thin films by improving material quality and effectively eliminating oxygen vacancies through a face-to-face post-annealing process under oxygen plasma environment. Annealing under oxygen plasma ensures the diffusion of atomic oxygen into the film to reduce the oxygen vacancies ( V O ). Simultaneously, the face to face placement of samples protects the sample surfaces being damaged by high energy oxygen ions and prevents the loss/re-evaporation of oxygen from the β -Ga 2 O 3 surfaces. After the oxygen plasma face-to-face annealing, the root–mean–square surface roughness of the thin film decreased from 14.9 nm to 7.5 nm, the surface V O decreased from 6.25 % to 2.88 %, and the full width at half maximum of the (-201) X-ray diffraction peak decreased from 0.129° to 0.093° With the apparent improvement of β -Ga 2 O 3 quality, the dark current of a Metal-Semiconductor-Metal photodetector is as low as 30 fA under a bias voltage of 10 V. The device has shown improved performance with the photo-to-dark current ratio of 6.06 × 10 7 , responsivity of 3.37 A/W, and the detectivity of 5.68 × 10 15 Jones.