Heat treatment effects in cadmium sulphide

Heating to temperatures in the range 300-550°K under broad-band illumination has been found to have a considerable effect on some optical and electrical properties of undoped and copper-doped cadmium sulphide single crystals and polycrystalline specimens. Changes observed in the characteristic emission bands at 0.73-0.78 μm, 1.06 μm and 1.5-2.2 μm have been correlated with changes observed in the thermally stimulated conductivity and in the spectral response of photoconduction at 90°K. Heat treatment is found to produce a centre which has a thermal activation energy of 0.86 ev for trapped electrons. The ratio of the optical to thermal activation energies for these trapped electrons is found to be approximately 1.95. The experimental results suggest that this centre contains a ground state which is common to both the 0.73-0.78 μm and 1.06 μm emission bands and which is also the excited state of the 1.5-2.2 μm emission bands. The centre is much more likely to be a complex association of defects than a single defect.