Improved Performance of Amorphous InGaMgO Metal-Semiconductor-Metal Ultraviolet Photodetector by Post Deposition Annealing in Oxygen

In this paper, the impact of O2 postdeposition annealing treatment on the material and UV detection characteristics of amorphous InGaMgO (IGMO) thin films was intensively studied. With the replacement of Zn by Mg, amorphous InGaMgO possesses an optical bandgap larger than that of the conventional amorphous InGaZnO by over 0.5 eV. Furthermore, it was found the post-deposition annealing in O2 effectively suppressed the oxygen vacancies in the amorphous IGMO thin film, resulting in a significant reduction in its dark current. Due to strong hole trapping, all the samples except the 480-min annealed one exhibited large photocurrent and accordingly high responsivity over $1\,\times \,10^{3}\,{\rm{A/ W}}$ @ 10 V. Moreover, both photocurrent and responsivity improve with increasing annealing time up to 240 min. As a result, the Metal-Semiconductor-Metal photodetector based on the 240-min annealed amorphous InGaMgO thin film exhibited a very prominent performance, including a high responsivity of $1.6\,\times \,10^{4}\,{\rm{A/ W}}$ and a large photo-to-dark current ratio of $1.3\,\times \,10^{3}$ . We attribute such excellent properties to the improved carrier mobility as well as the reduction of recombination centers in the O2-annealed film. However, some degradations in device performance were observed when the annealing time reached 480 min, which can be explained by the suppression of localized tail states, as demonstrated by the abruptly reduced Urbach energy, and accordingly the inhibition of related extrinsic excitation. This work has provided a promising candidate for the application in transparent contact-free interactive display.