Transition Metal-Doped Amorphous Oxide Semiconductor Thin-Film Phosphor, Chromium-Doped Amorphous Gallium Oxide

Transition metal (TM)-doped amorphous gallium oxide (a-GO:TMx) is studied as an inorganic thin-film phosphor. Cr is selected as an emission center based on preliminary screening. The most intense red photoluminescence (PL) with a broad emission band of 620-800 nm from the a-GO:Cr-x films deposited at room temperature is attained by optimizing the Cr concentration (x = 0.001) and the oxygen partial pressure (P-O2 = 10 Pa) during the film growth. Post-deposition thermal annealing at 400 degrees C in O-2, which is lower than the crystallization temperature, improves internal quantum efficiency (IQE) of PL to 0.3%. Crystallized films by 800 degrees C annealing further improves the IQE to 20%. The improvement of PL by crystallization is commonly observed for conventional inorganic phosphors, but opposite to that of previously reported rare-earth (RE)-doped a-GO:REx thin-film phosphors. It is explained by different solubility of Cr and RE in the beta-Ga2O3 host.