Browsing by Author "Nedeff, V."

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    Optical Properties of III–VI Lamellar Semiconductors Doped with Cu and Cd and of Related III–VI/Native Oxide Structures
    (American Scientific Publishers, 2011) Evtodiev, Silvia; Caraman, Iulia; Dmitroglo, Liliana; Leontie, L.; Nedeff, V.; Dafinei, A.; Lazar, G.; Evtodiev, I.
    GaS, GaSe and GaTe are typical representatives of III–VI layered semiconductor materials, showing highly anisotropic mechanical and optical properties. At photon energies hν < E g , the anisotropy ratio for the absorption coefficients at the n = 1 excitonic peak, corresponding to E →‖C → and E →⊥C → polarizations, is α ‖/α ⊥≈15. Optical functions n e (λ) and n o (λ) of GaS and GaSe in the wavelength range 0.36–22 μm have been determined. For the photon energies hν < E g ind, these correspond to a normal dispersion and can be described by power-law wavelength dependences. By means of FTIR transmission and reflection spectroscopy in the spectral range of 1000–85 cm−1, for plan-parallel plates with thickness between several tens of nanometers and centimeters, the wavenumbers of longitudinal optical ν(LO) and transverse optical ν(TO) phonons have been determined for GaSe [ν ⊥(LO) = 254 cm−1, ν ⊥(TO) = 214 cm−1], GaS [ν ⊥(LO) = 359 cm−1, ν ⊥(TO) = 297 cm−1, ν ‖(LO) = 336 cm−1], and GaTe [ν(LO) = 164 cm−1, ν(TO) = 118 cm−1].