We have investigated the optical properties of Te-doped ternary ZnSSe epilayers grown on (1 0 0) GaAs substrates by molecular-bean epitaxy for the first time. The case of ZnSxSe1-x-y:Te-y (x = 0.11, y = 0.032) specimen is represented by a good crystal quality; a good lattice matching to GaAs (Delta a/a < 0.19%), a rather small FWHM (<200 arcsec), and a large thermal activation energy (Delta E = 210 meV) in the thermal dissociation process of Te-n (n greater than or equal to 2) cluster emission, We have successfully fabricated ZnSSe:Te/ZnMgSSe DH-LEDs with an efficient blue-green emission (500 nm) and long-lived lifetime (> 1000 h) operated at 3 A/cm(2) (300 K).