Photoluminescence studies of CdS thin films annealed in CdCl₂ atmosphere

We have grown CdS films by the Close Spaced Vapor Transport technique under specific conditions: substrate temperature (Ts): 450 °C, source temperature (Tso): 725 °C, argon pressure in the chamber (PAr): 100, 200 and 500 mT, deposition time (td): 100 s. The films were studied by measuring the luminescence properties at different temperatures in the range 10-300 K. The room-temperature PL spectrum of the as-grown CdS films showed a very broad band centered at 2.26 eV and a shoulder in the low-energy side at 1.80 eV. After CdCl₂ thermal annealing at 300 K, the spectrum showed better PL characteristics: a strong band in the low-energy side at 1.67 eV and a band in the high-energy side at 2.47 eV. The analysis at lower temperatures showed that the high-energy band becomes most intense and shifts to higher energies reaching a value of 2.54 eV, very close to the energy band gap at 10 K. The low-energy band becomes broader and centered around 1.9 eV. Analysis of the PL intensity as a function of temperature in an Arrhenius representation, allows applying a theoretical model for the quenching of the PL intensity.