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 Zn1−zCdzSe 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-μm-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 107 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 <106 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/cm2) and maximum operating temperature (394 K).