PHOTOLUMINESCENCE ANALYSIS OF CDS THIN-FILMS UNDER PHASE-TRANSITION

Using the chemical bath deposition (CBD) method, CdS thin films in the cubic metastable phase were grown on glass substrates. On thermal ann ealing (TA) in Ar+S-2 atmosphere in the 240-510 degrees C temperature range, the samples transform to the wurtzite phase. This hexagonal cry stalline phase is the stable phase for CdS. From X-ray diffraction ana lysis the transition point from zincblende to wurtzite is found to occ ur in the 240-300 degrees C region. From photoacoustic absorption spec tra the energy band gap E(g) of the semiconductor was calculated. A pl ot of E(g) vs. TA shows a minimum value (2.28 eV) at 300 degrees C, in the region of the transition point. Photoluminescence measurements, i n the 1.40-2.60 eV emission energy range, show the 'well known' green emission band for the as-grown sample and for those annealed at high t emperatures (360-510 degrees C). For samples annealed in the intermedi ate region (240 and 300 degrees C), a second band located at 2.2 eV is present. This band, denominated the yellow band and arising in the re gion of temperature of the transition point, is ascribed to Cd interst itials. A mechanism relating the Cd interstitials to the phase transfo rmation is proposed.