The Study Of Photoelectric Properties Of Binary Oxide Semiconductor Heterojunction Films

The growing energy crisis and the current rate of pollution have made the efficient utilization of renewable solar energy in electrical and chemical transformations.The myriad of semiconductor-based systems have been extensively explored for photochemical applications.Among them,ZnO has attracted extensive interest due to its stable chemical properties,abundant raw materials and excellent photoelectric properties.However,the widespread technological use of ZnO is hindered by its low utilization of light in the visible range due to its wide band gap.For this reason,a variety of binary oxide materials are selected to modify the band structure of ZnO,such as the material matching visible light wavelength or the material with excellent photoelectric performance,and the heterogeneous structure is formed with ZnO to improve the utilization of visible light.Furthermore,its photoelectric performance was improved.In this paper,the CdO/ZnO/Ag and CdO/ZnO/Cu₂O heterostructure films were prepared by the laser molecular beam epitaxy（LMBE）.The structure,surface morphology,optical properties and the photoelectric response under the irradiation of visible light was mainly studied.The results are summarized as follows:（1）The CdO/ZnO/Ag films were fabricated on ITO substrates using the LMBE.The effect of Ag nanoparticles on the structure,optical properties and the photoelectric response have been investigated.The mechanism of the photoelectric properties for the films werealso discussed.No chemical reactions were observed between the CdO and ZnO films,and the Ag nanoparticles were well distributed on the ZnO film.Further studies indicated that the CdO and ZnO films had the cubic and hexagonal wurtzite structures,respectively.The enhanced absorption of the CdO/ZnO/Ag films was observed in the visible region compared to the pure CdO and ZnO films.Under visible light illumination,the photocurrent density of CdO/ZnO/Ag films at a bias voltage of 0.2 V was about 0.25μA/cm²,which was approximately 4 and 2.5 times higher than those of pure ZnO and CdO/ZnO films,respectively.The enhanced absorption and photocurrent response of the CdO/ZnO/Agfilms were attributed mainly to the reduced recombination rate of photogenerated electrons-holes pairs induced by localized surface plasmon resonance of Ag nanoparticles.（2）The CdO/ZnO/Cu₂O heterojunction films were fabricated on ITO substrates using the LMBE.The morphology,structure,optical properties and the photoelectric response were studied.The surface of the films was flat and dense,and the films had a uniform particle size distribution with the grain size of about 40 nm.The films exhibited（002）and（200）orientations for ZnO and CdO,respectively.The absorption enhancement of the CdO/ZnO/Cu₂O heterojunction films in the visible region was observed as compared to pure ZnO and CdO/ZnO films.Under visible light illumination,the photocurrent density of CdO/ZnO/Cu₂O heterojunction films at a bias voltage of 0.2 V was about 0.55μA/cm²,which was approximately 7.8 and 4.6 times higher than those of pure ZnO and CdO/ZnO films,respectively.The formation of p-n junction between ZnO and Cu₂O promoted the separation of photogenerated electrons-holes pairs,which improved the absorption and photocurrent response under visible light illumination.