Preparation And Properties Of Al Doped CdO-ZnO Composite Films

Transparent conductive oxides have been widely used in solar cells,phototransistors and other fields.Among various transparent conductive oxides,zinc oxide(ZnO)and cadmium oxide(CdO)are widely concerned because of their excellent optical and electrical properties.It is possible to obtain the best properties of ZnO films with low resistivity and high transmittance in visible light range and CdO films with the high carrier mobility and high transmittance in near-infrared range for the film composed of CdO and ZnO.Therefore,a series of CdO-ZnO composite films were prepared by magnetron sputtering in this thesis,and Al was doped in the composite films.The structure,optical properties and electrical properties of CdO-ZnO composite films were studied systematically.When the ratio of CdO and ZnO is 4:1,the XRD mainly shows the characteristic peak of CdO(200),and when the ratio of CdO and ZnO is 3:2,XRD mainly shows the diffraction peak of CdO(111).With the further reduction of CdO content,when the ratio of CdO and ZnO is 2:3 and 1:4,the intensity of the ZnO(002)diffraction peak is significantly enhanced,while the intensity of the CdO(200)diffraction peak decreases sharply.The CdO-ZnO(4:1,3:2,2:3,1:4)thin films have good crystallinity,smooth surface and dense crystal grains.The maximum transmittance of all CdO-ZnO thin films in the visible and infrared regions has been above 80%,and the maximum transmittance of CdO-ZnO(2:3)thin films in the visible region has reached 91.18%,and the maximum transmittance in the infrared region has been up to 90.19%,the optical transmittance of thin films has been increased by doping.The optical bandgap of CdO-ZnO(4:1,3:2,2:3,1:4)thin films has varied in the range of 2.63-3.63 eV,and the preparation of composite films has realized the modulation of the bandgap.When the content of CdO increased from 20%to 80%,the CdO-ZnO thin film resistivity decreased from 27.35×10-3 to 10.79×10-3 Ω·cm.The resistivity of the film can be reduced by doping,so CdO-ZnO film with high conductivity and light transmittance is expected to be obtained through doping.The Al:CdO-ZnO(1:4)films with a dense and smooth surface were prepared in the range of Al target doping power of 5-20W.The doping of Al changed grain structure change from the long strip to the round grain and refined the grain size.The optical transmittance of Al:CdO-ZnO(1:4)film is over 85%in the visible and infrared light regions,which is only slightly lower than that of the undoped CdO-ZnO film.The band gap value of Al:CdO-ZnO(1:4)is between 3.55-3.67eV.After Al doping,the conductivity of CdO-ZnO thin film has been improved,and the resistivity gradually decreases from 25.64×10-3 to 2.55×10-3Ω·cm with the increase of doping power.The high optical transmittance is retained and the resistivity is further reduced.