Effect of Chlorine Doping on the Optical Properties of Vacuum-Evaporated ZnTe Thin Films

ZnTe thin films of varying thicknesses (3000-6000 Å) were successfully prepared on glass substrates using the high vacuum evaporation (HVE) technique. Chlorine doping was performed by immersing the films in an aqueous bath (containing ZnCl<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> + distilled water) at different concentrations (from 5% to 20%) for various immersion times. The thicker films were annealed (in a vacuum to analyze optical properties and in air to evaluate electrical properties) for 1 hour at different annealing temperatures (RT-300 °C) to examine the effects of annealing. The electrical resistivity of the Cl-doped ZnTe films decreases as the concentration of the Cl dopant increases. The optical band gap increases with increased dopant concentration. The optical constants (the refractive index and the extinction coefficient) decrease with Cl doping. Photoluminescence measurements of the films were conducted using emission spectra by exciting the samples with various excitation wavelengths. The films exhibited noticeable fluorescence at specific excitation wavelengths, displaying green and yellow emission bands. The quantum yield of the PL peaks was evaluated. The results indicate that Cl-doped ZnTe films are promising absorber layers for thin-film solar cells.