Abstract
AbstractThe absorption and reflection coefficients of GeSe single crystals are measured at various temperatures in the spectral range 0.8 to 2.2 μm using linearly polarised light. The main absorption mechanism is due to indirect interband electronic transitions with participation of two different phonons. Indirect energy gap values of 1.22 and 1.18 eV are obtained for the two directions of polarisation ϵ ∥ a and ϵ ∥ b, respectively. The corresponding phonon energies at room temperature are found to be 0.023 and 0.089 eV for ϵ ∥ a and 0.013 and 0.043 eV for ϵ ∥ b. The indirect gaps vary linearly with temperature, the temperature coefficient being −8.68 × 10−4 and −5.05 × 10−4 eV K−1 for the two directions of light polarisation, respectively. A donor‐like localised level within the energy gap of GeSe, lying 0.55 eV above the valence band irrespective of direction, is found from the tail of the room temperature absorption curves. Since a similar level has been observed previously in amorphous GeSe it is assumed to be an intrinsic property, introduced by Se vacancies.
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