Preparation Of Rare-Earth Doped CdTe Thin Films By Double Source Vacuum Co-Evaporation

Double source vacuum co-evaporation was utilized to prepare pure CdTe thin films and CdTe thin films of rare-earth elements (Y,Gd) doped on glass substrates. The heat-treatment was conducted in N2 environment. The effects of different heat-treatment conditions and doping currents on properties of thin films were studied. The crystalline structure, surface morphology and roughness, chemical composition, optical and electronic properties of thin films were characterized by X-ray diffraction, atomic force microscope, scanning electron microscopy with energy dispersive analysia, X-ray photoelectron spectrum, ultraviolet-visible spectrophotometer, desktop multimeter, respectively.Experimental results show that the thin films, which was deposited under the optimal atomic ratio(Cd:Te= 1:0.6), were cube sphalerite structural of CdTe with [111] preferred orientation by method of heat-treatment in N2 for 20mins at 400℃. The thickness of thin film is 250nm. The morphology of the thin films were even and rare. The average grain size and surface roughness were 26.88nm,10.9nm, respectively. Stoichiometries of surface and body's elements(Cd,Te) in thin film were 1:0.9,1:1.3. The absorption coefficient was great and the optical bandgap was 1.452 eV. The conductor type and resistance of thin film were P-type and 10.8Ω·cm.Researches indicate the optimal heat-treatment condition of pure CdTe thin film is T=400℃,t=20min.Experiments find that the crystalline structure, conductor type of thin films kept unchanged when CdTe thin films doped Y and Gd. The lattice constant, crystal cell volume of CdTe thin film turned small by doping Y, doped-Gd was opposition. Doping Y or Gd could make the sureface of the CdTe thin film turn compact and homogeneous, on which grain size is uniformity,while ajust percent contents of surface and bulk elements of the CdTe thin film, Stoichiometries of which closed to standard stoichiometry, and change optical absorption and resistance of the CdTe thin film. Doped-Y could make absorption limt of the thin film move to long wave, which happed Einstein shift, doped-Gd was opposition. The appropriate content could let the optical bandgap energy of the CdTe thin film close the optimal bandgap value of the solar cell, the resistance of thin films drop 10-3-10-5Ω·cm amount range.