Temperature-Dependent Crystallization of Ga2O3 for Ultraviolet Photodetectors

As an n-type oxide semiconductor, Ga2O3 shows great promise in solar-blind ultraviolet (UV) photodetectors due to its adequate band gap, high absorption coefficient, high thermal and chemical stability, high breakdown voltage, and high sensitivity to UV light. In order to investigate the photoresponse of the Ga2O3 photodetector with different crystallization status, we fabricated a series of beta-Ga2O3 thin films on a sapphire substrate via pulsed laser deposition with different deposition temperatures from 250 degrees C to 650 degrees C. X-ray diffraction and scanning electron microscopy result showed crystallization enhancement due to the increasing of deposition temperature, and the crystallization procedure started at similar to 450 degrees C. Optical analysis indicated a blue shift present at the absorption edge (from 4.6 eV to 5.1 eV) with temperature increasing from 450 degrees C to 650 degrees C, showing modulation feasibility in the band gap due to temperature dependence. In addition, all samples showed high transmittance (over 90%) over the entire visible spectrum. Film detectors fabricated by these samples showed high photoresponse and high light/dark current ratio (I-Light/I-Dark) on Ga2O3 deposited at 450 degrees C. Transmission electron microscopy result for film deposited at 450 degrees C showed that the top and bottom regions of films contained both amorphous and crystalline Ga2O3, while there was no crystallization in the middle area of the film, indicating that a combined amorphous-crystalline Ga2O3 film with adequate ratio of crystalline state can significantly enhance the photoresponse while restraining the dark current.