P-type Transparent Conducting Cu-al-o Films With Optical And Electrical Properties

Based upon the theory of "the chemical modulation of the valence", the delafossite structure,p-type and directly band-gap electrical conductivity transparent oxide thin film of CuAlO₂ was designed by Kawazoe etc.in 1997 for the first time.The discovery of p-type TCO made possible the fabrication of transparent oxide optoelectronic devices such as transparent p-n junction diodes and transistors using an appropriate combination of p- and n-type TCO films,which also led TCO material to the frontier of transparent oxide semiconductor(TOS). CuAlO₂ has become one of the research hotspots in transparant conductive films fields.In this paper,p-type transparent conducting Cu-Al-O films were prepared by using direct current(dc)magnetron reactive co-sputtering deposition with Cu and Al metallic targets.The samples were characterized by atomic force microscopy(AFM),X-ray diffraction (XRD),4-point probe,UV-VIS spectrophotometer,respectively.The influence of the annealing temperature,Oxygen argon(O₂/Ar)ratio and sputtering power on the optical and electrical properties were studied.XRD analyses indicate that Cu-Al-O films are polycrystalline structure and the crystallinity is improved by appropriate annealing treatment.AFM results show that the surfaces morphology of the films was smooth and the surface roughness was small.The films are composed of some excellent columnar crystallites.The XPS results indicate that the Cu mostly exist as + 1 valence charge and Al exist as +3 valence charge,this is the same with CAO.The analysis of the electrical properties indicate that annealing temperature,oxygen argon ratio and sputtering power of the Al target have strong influence on the properties of Cu-Al-O films.With the increase of the annealing temperature and oxygen argon ratio,the resistivity of the films decreased.With the increase of the sputtering power of the Al target,the resistivity are decreased,and then increased.The spectral analysis results indicate that the transmission rate of the thin film in visible region can reach 72%.With the increase of the oxygen argon ratio and sputtering power of the Al target,the transmission rate are gradually increased.The calculation results indicate that films' band gaps changed in range of 3.0-3.8 eV.Based on the studies of the structural,optical and electrical properties of Cu-Al-O thin films,it can be obtained the optimal deposition conditions of Cu-Al-O thin films by direct current reactive magnetron co-sputtering with Cu and Al metallic targets.The oxygen argon ratio,deposition temperature,gas pressure,sputtering power and annealing temperature were 2:3,300℃,3 Pa,Cu target:20 W,Al target: 60 W,1000℃,respectively.