Long-range atomic order in ${\mathrm{Ga}}_{\mathrm{x}}$${\mathrm{In}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{As}}_{\mathrm{y}}$${\mathrm{P}}_{1\mathrm{-}\mathrm{y}}$ epitaxial layers [(x,y)=(0.47,1), (0.37,0.82), (0.34,0.71), and (0.27,0.64)]

Transmission-electron microscopy and selected-area diffraction have been used to study ${\mathrm{Ga}}_{\mathrm{x}}$ ${\mathrm{In}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{As}}_{\mathrm{y}}$ ${\mathrm{P}}_{1\mathrm{-}\mathrm{y}}$ [(x,y)=(0.47,1), (0.37,0.82), (0.34,0.71), and (0.27,0.64)] alloy semiconductors. A systematic analysis of edge-on and plane-view samples has shown that an ordered phase closely related to the CuPt-type structure exists in these materials. Only two of the possible four {111}-ordered variants are observed. An attempt is made to rationalize this observation and a detailed account of atomic ordering in these alloys (for a range of values of x and y) is presented.