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 $\text{E<1.5\hspace{0.17em}}\mathrm{eV}$ is in excellent agreement with that for the single crystal. The optical absorption coefficient was determined in the $\text{E<3.5\hspace{0.17em}}\mathrm{eV}$ range and was compared with that for the single crystal. The results revealed two direct allowed transitions at 1.50 eV $[{\mathrm{\Gamma }}_{\mathrm{8}}{\mathrm{\hspace{0.17em}valence\hspace{0.17em}band(VB)\to \Gamma }}_{\mathrm{6}}\mathrm{\hspace{0.17em}conduction\hspace{0.17em}band(CB)}]$ and 2.43 eV $[{\mathrm{\Gamma }}_{\mathrm{7}}{\mathrm{(VB)\to \Gamma }}_{\mathrm{6}}\mathrm{(CB)}]$ and three indirect allowed transitions at 1.27 eV ${\mathrm{[L}}_{\text{4,5}}\mathrm{(VB)}{\mathrm{\to \Gamma }}_d\mathrm{],}$ 1.83 eV ${\mathrm{[L}}_6\mathrm{(VB)}{\mathrm{\to \Gamma }}_d\mathrm{],}$ and 2.84 eV $[{\mathrm{\Gamma }}_{\mathrm{8}}{\mathrm{(VB)\to L}}_{\mathrm{6}}\mathrm{(CB)}\mathrm{].}$ 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 ${\Gamma }_d,$ 0.65 eV above ${\Gamma }_8$ (VB). The indirect transitions at 1.83 and 2.84 eV are assisted by phonons having energies of 80 and 84 meV, respectively.