Low-temperature midinfrared absorption in GaSe

We report the measurement of the temperature dependence of the absorption spectra of epsilon- GaSe over the temperature range 300 K to 5 K. Measurements have been made for both the e-ray (polarized parallel to the crystal's c-axis) and the o-ray (polarized perpendicular to the c-axis), over the spectral range 4000 to 10 cm(-1). Nine absorption lines at 417, 440, 499, 546, 891, 945, 1015, 1093, 1270 cm(-1) were recorded at 300 K for the e- ray spectra. Some of these lines were identified using the results of a modified single layer, linear chain model of GaSe. The lines at 417, 440 and 499 cm(-1) were assigned to local impurity absorption originating from N, Mg and O, respectively. The weak lines at 945, 1015 and 1093 cm(-1) were assigned to hole transitions from the acceptor levels to the top of the valence band. Two absorption lines at 891 cm(-1) and 1270 cm(-1) were assigned to hole transitions from the quasi-local acceptor levels to the double degenerate valence sub-bands Gamma(5) or Gamma(6). The origin of lines recorded in the far IR absorption spectra at 20, 37 cm(-1) and 362 cm(-1) were also identified.