ZnO thin film is the perspective material for using as active layer in solid-state UV photodetectors. Here we present our investigations of photoelectric properties of the developed photosensitive field-effect transistor. Pure and lithium doped ZnO films were produced by vacuum electron-beam deposition method. Field effect was studied in Li doped ZnO films having high resistivity and in heterostructures consisting of three ZnO layers doped by 1, 5 and 10 at% of Li impurity accordingly. The photoelectric characteristics were measured (currents ratio, charge carriers mobility, ampere-watt sensitivity in UV diapason, NEP sensitivity, and photocurrent kinetics). The open and close current ratio was 106 and the field-effect mobility was ~10 cm2/Vsec. We have also studied the low-frequency noises (0.001÷100 kHz) of UV photodetector and suggested the methods of noise suppression. It was found that the dark current noises and photocurrent noises have different mechanisms.