Crystal-Phase Dependence of Solar-Blind UV Photodetector Performance: A Comparison of ε-, β-, and ε/β-Mixed Ga 2 O 3

Abstract Ga 2 O 3 -based solar-blind ultraviolet (UV) photodetectors demonstrate significant potential in critical fields including fire early-warning, ozone layer monitoring, and space communication. However, systematic exploration into the effect of different phase structures of Ga 2 O 3 on photoelectric detection performance remains limited. In this work, ε-, β-, and ε/β-mixed Ga 2 O 3 thin films were grown on sapphire substrates by atomic layer deposition (ALD) technology. The properties of the grown films and prepared solar-blind UV photodetectors were comparatively investigated. Due to the lower lattice mismatch with the sapphire substrate, ε-Ga 2 O 3 film exhibits superior crystallinity and the lowest oxygen vacancy concentration, enabling the ε-Ga 2 O 3 -based photodetector to achieve the fastest photoresponse speed (rising/decaying times of 147/55 ms). β-Ga 2 O 3 film was obtained by an annealing process under a reducing environment that introduced a high concentration of oxygen vacancies. As a result, β-Ga 2 O 3 -based photodetector exhibits the highest photocurrent (94 μA) and responsivity (107 A/W). For mixed-phase Ga 2 O 3 , the rough surface and internal grain boundaries may reduce carrier mobility, which makes the dark current of the photodetector as low as 38 pA, and helps to achieve a high photo-to-dark current ratio of 1.3×10 6 and a detectivity of 3.42×10 14 Jones. This result is rather important as the crystal-phase dependence of films controls the properties of structure, morphology, and chemistry, which influences the optical characteristics and fabricated photodetectors performance.