Analysis on the structural, vibrational and defect states of chlorine treated polycrystalline cadmium telluride structures grown by e-beam evaporation

Temperature dependent photoluminescence (PL) measurements are performed in order to study the defect states in cadmium chloride treated polycrystalline cadmium telluride (CdTe) thin films grown by e-beam evaporation technique. Three luminescence bands are observed including a double peak emission at 1.577 eV and 1.573 eV corresponding to free electron-to-acceptor transition and a donor-acceptor pair (DAP) transition, respectively, along with a broad peak at 1.45 eV. This broad band emission is related to A-center chlorine based complex and also includes longitudinal (LO) phonon emission lines for CdTe spaced by similar to 21 meV. Investigation into grain sizes revealed grains of 0.2 mu m for as-grown films and similar to 2-3 mu m for chlorine activated films shown by atomic force microscopy (AFM). Raman analysis indicates that the films have been grown with excess of Te leading to p-type conductivity in the structure, whereas LO phonon mode of polycrystalline CdTe reveals quasi phonon modes nature.