Transition metal Copper doped Cadmium oxide and (Cu: CdO and n-CdO: Cu / p-Si) thin films were prepared onto glass and p-type single crystal (111) Si substrates at temperature 300 K by thermal evaporation technique with thickness (400±30) nm. The effects of different Cu ratios on the CdO thin films and heterojunction of n-CdO / p-Si.. The X-ray diffraction analysis approves the CdO films are polycrystalline and cubic structure with lattice parameter of 0.4689 nm. The optical transmittance exhibits excellent optical absorption for 6% Cu doping. Decreased of optical band gap from 2.1 to 1.8 eV. Hall measurement approves that CdO material n type with a maximum carrier mobility of 144.6 (cm2 /Vs) with resistivity of 0.107991 (Ω.cm) were achieved for 6% Copper (Cu) doping. The I-V characteristics of heterojunction prepared under illumination was carried out by(100 mW/cm2) incident power density at different Cu doping.