Investigation of the Light Absorption Mechanisms near Exciton Resonance in Layered Crystals

Wide temperature range (4.5 to 300 K) exciton absorption spectra of pure, doped and GaSe crystals intercalated by manganese have been studied. It has been shown that at low temperatures in p-type GaSe crystals the degeneration in the momentum space of then= 1 exciton band with holes localized in quantum wells leads to suppression of the exciton oscillator strength fexc. The slight doping (0.1 wt%) of GaSe by Mn impurities compensates holes and restores the polariton light absorption mechanism. The oscillator strength of the exciton and band-to-band optical transitions fexc = fcv = 0.05, plasma frequency ωp = 2.9 × 1014 s—1, and value of longitudinal-transversal splitting ΔL-T = 0.4 cm—1 of polariton branches have been found for GaSe crystals. It is assumed that a slight excess of fexc over fcv in intercalated GaSe crystals occurred due to the participation of the “indirect phototransition” mechanism in the light absorption when the excitons undergo an additional scattering on local interlayer optical vibrations.