The photoluminescence (PL) and electrical properties of AlGaN/GaN high electron mobility transistors (HEMTs) with different Fe doping concentrations in the GaN buffer layers were studied.It was found that,at low Fe doping concentrations,the introduction of Fe atoms can result in a downward shift of the Fermi level in the GaN buffer layer,since the Fe atoms substitute Ga and introduce an FeGa3+/2+ acceptor level.This results in a decrease in the yellow luminescence (YL) emission intensity accompanied by the appearance of an infrared (IR) emission,and a decrease in the off-state buffer leakage current (BLC).However,a further increase in the Fe doping concentration will conversely result in the upward shift of the Fermi level due to the incorporation of O donors under the large flow rate of the Fe source.This results in an increased YL emission intensity accompanied by a decrease in the IR emission intensity,and an increase in the BLC.The intrinsic relationship between the PL and BLC characteristics is expected to provide a simple and effective method to understand the variation of the electrical characteristic in the modulation Fe-doped HEMTs by optical measurements.