STRUCTURAL CHARACTERIZATION OF II-VI SEPARATE-CONFINEMENT HETEROSTRUCTURE LASERS WITH ZN1-XMGXSYSE1-Y CLADDING LAYERS

We have investigated the structural characteristics of II-VI separate confinement heterostructure lasers grown on GaAs substrates and containing Zn1-xMgxSySe1-y quaternary cladding layers, ZnSe or ZnSySe1-y guiding layers and Zn(1-z)Cd(z)e quantum well active layers. The study was performed with a combination of transmission electron microscopy and high resolution x-ray diffraction techniques. We found that the quaternary cladding layers remain pseudomorphic to the GaAs substrate although they can be lattice mismatched up to 0.1%. When the 0.5-mu m-thick optical guiding layer contains ZnSe, there is partial relaxation of the laser structure by misfit dislocations at the lower cladding-guiding layer interface and the threading dislocation density in the Zn1-zCdzSe quantum well active region is about 10(7) cm(-2). However, when lattice matched (to GaAs)ZnSySe1-y is used as the guiding layer the entire laser structure is pseudomorphic and the threading dislocation density is <10(6) cm(-2) The combination of low defect density and enhanced carrier and optical confinement by using Zn1-xMgxSySe1-y quaternary cladding layers has produced significant improvement in the room temperature threshold current (500 A/cm(2)) and maximum operating temperature (394 K).