TEMPERATURE-DEPENDENCE OF EXCITON REFLECTION SPECTRA IN MONOCLINIC ZINC DIPHOSPHIDE

Reflection spectra near the fundamental edge of monoclinic ZnP2 crystal have been measured at various temperatures from 2 K to 200 K. As the temperature is raised from 2 to 80 K, minimum value of the reflectivity R(min) due to the lowest 1s exciton is found to decrease. The R(min) turns to increase above 80 K. The model calculations of reflection spectra based on the dead layer model are performed for different values of the exciton dissipative damping constants. The analysis of the reflection spectra obtained at various temperatures reveals that this change of the spectra results from monotonical increase of the exciton damping with increasing temperature in the existence of exciton-free "dead layer". It is suggested that the main contribution to the exciton damping is the scattering by phonons.