Stimulated and spontaneous emission studies in ZnS1-xTex/ZnSe strain layer superlattices

The optical and light emitting properties of ZnSTe/ZnSe strained superlattices are investigated. The hhl-el exciton absorption peak is observed both in absorption and photoluminescence excitation spectra at low temperatures. The Stokes shift between the photoluminescence and absorption peak is similar to 6 meV indicating that the recombining excitons are only weakly localized and that the sample quality is high. Strong exciton-phonon coupling in the ZnSe wells is evidenced from the observation of oscillatory peaks with energy separation of 31 meV in the PLE spectra. These result from hot excitonic creation and subsequent relaxation via multiple longitudinal-optical phonon emission. Room-temperature stimulated emission by photopumping in the deep-blue spectral region is also observed. An upper limit of the threshold carrier density required to achieve lasing is estimated to be similar to 5 X 10(18)/cm(3) for the ZnSTe/ZnSe superlattices.