Effect of N doping on the structural properties of ZnSe epitaxial layers grown by molecular beam epitaxy

The structural properties of ZnSe doped with N, in the concentration range of 1×1018–2×1019 cm−3, were characterized by transmission electron microscopy, x-ray diffraction, and Raman spectroscopy techniques. The relaxation of the lattice mismatch induced compressive strain between ZnSe and GaAs is less for N doped layers for a given ZnSe thickness. The smaller amount of strain relaxation with N doping results in layers that contain residual compressive strain up to thicknesses of at least 1.7 μm. In addition, the misfit dislocation array becomes a regular rectangular grid when N is incorporated in ZnSe layers. The ZnSe lattice constant, as measured by x-ray diffraction, decreases as the N concentration increases. The reduction in lattice constant, however, is greater than can be explained by the shorter Zn-N bond distance of model predictions. We attribute the excess lattice contraction to the generation of point defects accompanying N doping. The Raman spectra display a broadening of the linewidth as the N concentration increases, which supports the notion of point defect creation with N doping.