Thin film transistor, method of fabricating a thin film transistor and flat panel display device having the same

A thin film transistor (TFT) includes a substrate, a transparent semiconductor layer on the substrate, the transparent semiconductor layer including zinc oxide and exhibiting a charge concentration of about 1×1014 atom/cm3 to about 1×1017 atom/cm3, a gate electrode on the substrate, a gate insulating layer between the gate electrode and the transparent semiconductor layer, the gate insulting layer insulating the gate electrode from the transparent semiconductor layer, and source and drain electrodes on the substrate, the source and drain electrodes being in contact with the transparent semiconductor layer.