We report the results of an investigation of the structural properties and relaxation of misfit stress with transmission electron microscopy and x-ray diffraction techniques. Epitaxial films of ZnSe were grown on GaAs by molecular-beam epitaxy of thicknesses ranging from 0.05 to 4.9 μm. The films contain stacking fault defects up to thicknesses of about 150 nm. Above 150 nm perfect misfit dislocations are generated from surface sources and the stacking fault defects to accommodate the lattice mismatch. The majority of dislocations observed are of the 60° type with Lomer edge type dislocations observed in a much lower concentration. The density of misfit dislocations increases with increasing epilayer thickness. Above about 1 μm the films exhibit biaxial tension which we believe is due to thermal expansion differences of ZnSe and GaAs. Good agreement is observed between microscopic and diffraction measurements of the relaxation phenomena.

We describe the performance of blue-green injection lasers containing Zn1−xMgxSySe1−y cladding layers. The devices have yielded the lowest reported threshold current densities (500 A/cm2) and the highest reported pulsed output powers (500 mW) at room temperature. Lasing has been observed at temperatures as high as 394 K. The room temperature and 85 K lasing wavelengths are 516 and 496 nm, respectively. The use of Zn1−xMgxSySe1−y, instead of ZnSzSe1−z, cladding layers provides a clear improvement in optical confinement, demonstrated by the widening of the far-field pattern in the direction perpendicular to the layers. The lasers are separate-confinement heterostructures with a ZnS0.06Se0.94 waveguiding region and a single Cd0.2Zn0.8Se strained quantum well. The entire structure is pseudomorphic with the GaAs substrate.

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