Temperature dependence of exciton peak energies in ZnS, ZnSe, and ZnTe epitaxial films

High-quality ZnS, ZnSe, and ZnTe epitaxial films were grown on (001)-GaAs-s ubstrates by molecular beam epitaxy. The 1s-exciton peak energy positions h ave been determined by absorption measurements from 2 K up to about room te mperature. For ZnS and ZnSe additional high-temperature 1s-exciton energy d ata were obtained by reflectance measurements performed from 300 up to abou t 550 K. These complete E-1s(T) data sets are fitted using a recently devel oped analytical model. The high-temperature slopes of the individual E-1s(T ) curves and the effective phonon temperatures of ZnS, ZnSe, and ZnTe are f ound to scale almost linearly with the corresponding zero-temperature energ y gaps and the Debye temperatures, respectively. Various ad hoc formulas of Varshni type, which have been invoked in recent articles for numerical sim ulations of restricted E-1s(T) data sets for cubic ZnS, are discussed. (C) 1999 American Institute of Physics. [S0021-8979(99)06420-8].