Electrodeposited CdTe—optical properties

For the measurement of optical constants, the electrodeposited films of CdTe were lifted off their opaque substrates and transferred onto glass slides using a transparent liquid adhesive. This technique proved to give results more reliable than those obtained on samples in which CdTe is deposited on CdS-coated conducting glass. The measured optical dispersion in the photon energy range of E<1.5 eV is in excellent agreement with that for the single crystal. The optical absorption coefficient was determined in the E<3.5 eV range and was compared with that for the single crystal. The results revealed two direct allowed transitions at 1.50 eV [Γ8 valence band(VB)→Γ6 conduction band(CB)] and 2.43 eV [Γ7(VB)→Γ6(CB)] and three indirect allowed transitions at 1.27 eV [L4,5(VB)→Γd], 1.83 eV [L6(VB)→Γd], and 2.84 eV [Γ8(VB)→L6(CB)]. The 1.27 and the 1.83 eV transitions, which have not been reported previously and were not detected in single-crystal data, are attributed to the transitions to a grain-boundary-related defect energy band Γd, 0.65 eV above Γ8 (VB). The indirect transitions at 1.83 and 2.84 eV are assisted by phonons having energies of 80 and 84 meV, respectively.