Strain effects on the energy band-gap in oxygenated CdTe thin films studied by photoreflectance

The incorporation of oxygen during the preparation of sputtered CdTe films produces a strong strain of the zincblende (cubic) lattice. First as a cons equence of this, the energy band-gap shifts to lower energies and then, far larger strains, the degeneracy of the hole valence bands splits into two b ands at the fundamental band-gap. These two transitions were measured using photoreflectance spectroscopy (PRS) as a function of the oxygen content. T he energy band-gap shift resulting from tensile stress in the films was cal culated using the elastic constants and deformation potentials for CdTe as well as the measured interplanar spacing values of the (1 1 1) CdTe X-ray d iffraction peak. (C) 1999 Elsevier Science Ltd. All rights reserved.