Optical Properties and Lasing in CdSe-Submonolayers in a (Zn,Mg)(S,Se) Matrix

We have proposed and realized a new type of optoelectronic structures we refer to as excitonic waveguides which allow an ultimate shift towards the violet spectral range (460 nm at 300 K for the ZnMgSSe/GaAs materials system). The excitonic waveguiding effect is realized at the low energy side of the strong exciton absorption peak due to localized states, caused by ultrathin narrow-gap insertions. To realize the zero-phonon lasing mechanism resonant to the spectral region of resonantly enhanced refractive index one needs to break the k-selection rule preventing direct radiate exciton recombination having large in-plane k-vector dominating at high excitation densities and observation temperatures. This can be done by localizing excitons at nanoscale CdSe-rich islands formed by ultrathin CdSe insertions.