Quantum confinement effects of CdTe nanocrystals sequestered in TiO2 matrix: effect of oxygen incorporation

Thin films of TiO2 with high volume fraction ∼(40-55%) and crystallite size ∼(6-40 nm) of CdTe nanoparticles had been prepared by rf magnetron sputtering from a composite TiO2:CdTe target at room temperature and 373 K. A detailed optical properties of nanocrystalline CdTe:TiO2 films as-deposited and after thermal treatment (⩽300 °C) are studied. The absorbance of the TiO2 films with CdTe nanocrystallite dispersions depends both on the nanocrystallite size and volume fraction. The blue-shifts of the optical absorption edge concurrent with the CdTe nanocystal size reduction for as-deposited and after thermal treatment of nanocrystalline CdTe:TiO2 thin films with respect to the bulk semiconductor agrees quite well with the strong quantum confinement theory. A slight deviation in absorption edge values than the predicted values from the strong quantum confinement model can be attributed to change in interplanar distance due to oxygen incorporation and inhomogeneous size distribution of CdTe nanocrystallites in these films.