Abstarct: Abstract In this thesis, the physical properties of MoO3 thin films, as well as the properties of n-MoO3/p-Si heterojunction UV and IR photodiode, also Au/MoO3/Au configuration (MSM) UV photodetector, were prepared and investigated by thermal oxidation and reactive sputtering methods. In this research for characterizations of the studied samples we used: the field emission scanning electron microscope (FESEM), Energy Dispersive X-ray (EDX), X-ray diffraction (XRD), Raman Spectroscopy, UV-Vis. Spectroscopy, Photoluminescence (PL), and the current-voltage (I-V) in dark and under illumination conditions. First, we synthesized molybdenum oxide films by the methods of thermal oxidation of the molybdenum mextal film and the reactive sputtering method on the glass substrate. It was found that the sample prepared with 60 sccm flow of oxygen gas (Sample G60) has optimal optical and electrical conditions, in the samples prepared by reactive sputtering, sample SR400, annealed at 400 ℃, and has optimal optical and structural growth conditions. Next, in order to investigate the photodiode properties and photodetector UV and IR, the obtained films with the optimal conditions for the preparation of n-MoO3/p-Si heterojunction photodiode and the Au/MoO3/Au photodetector were prepared by thermal oxidation and reactive sputtering on the silicon substrate. It was found that the sample prepared with the optimal conditions obtained in the thermal oxidation method has the highest photo-response ratio to infrared (17) and ultraviolet (11.6) radiation. Also, for samples prepared under optimal conditions by a reactive sputtering method, the highest optical response ratio to infrared (650) and ultraviolet (455) radiation belongs to the model prepared with gas flow (Ar/O2:12/3 sccm).