Donor bound-exciton excited states in zinc selenide

Abstract

Accurate measurements of donors in selective photoluminescence (SPL) and photoluminescence excitation (PLE) spectra have been made with a tunable dye laser for relatively pure vapor and solution-grown single crystals of ZnSe. The donor species are identified by reference to the work of Merz et al. Very accurate agreement is found for the $1s-2s,p$ excitation energies, though not for the absolute photon energies. A new bound exciton (BE) falling just above the donor BE is shown not to involve a further donor species. Improved values are derived for effective-mass donor binding energy, the electron effective mass, static dielectric constant, internal binding energy of the free exciton (FE), and the free-particle band gap in ZnSe. Large differences in the PLE spectra of excitons bound to ionized compared with neutral donors, as well as for neutral acceptors and other BE, are attributed to the dominance of free electron-hole pairs in the excitation channel for the former and FE for the latter luminescence. Landau-level effects appear in the PLE for ionized donor luminescence. New excited BE states appearing just below the $n=2\mathrm{}$ FE energies are shown by SPL to involve neutral donors. Their wave-function character is contrasted with the donor bound-exciton excited states just below the $n=1\mathrm{}$ FE. The nature of splittings observed in ionized donor BE is discussed.