STRUCTURAL-PROPERTIES OF NITROGEN-DOPED ZNSE EPITAXIAL LAYERS GROWN BY MBE

We have used transmission electron microscopy (TEM) and high-resolutio n x-ray diffraction (HRXRD) techniques to investigate the structural p roperties of ZnSe doped with nitrogen, in the concentration range of 1 x 10(18) to 2 x 10(19)cm-3. The nitrogen-doped layers contain substan tial residual compressive strain at layer thicknesses where undoped Zn Se would be completely relaxed. The residual strain is clearly observe d both in the inequality of the lattice constants (measured by HRXRD) parallel and perpendicular to the growth direction, and in the reducti on of the misfit dislocation density (measured by TEM) relative to und oped ZnSe. In addition to the reduction in dislocation density, the mi sfit dislocations form a regular rectangular grid, rather than the irr egular array seen in undoped ZnSe. The effective relaxed ZnSe lattice constant, as measured by x-ray diffraction, decreases as the nitrogen concentration increases. For the highest nitrogen concentration, this reduction in lattice constant, however, is greater than can be explain ed by the shorter Zn-N bond distance of theoretical predictions.