Anisotropic resistivity correlated with atomic ordering in p-type GaAsSb

We have detected three- and six-fold lateral ordering in undoped and carbon -doped GaAs1-xSbx films (0.4 <x <0.6), using plan-view and cross-sectional transmission electron microscopy. The samples were grown by organometallic vapor phase epitaxy onto oriented InP (001) substrates, at temperatures ran ging from 500 to 600 degreesC. Spontaneous lateral superlattices with modul ation parallel to the [110] in-plane direction occur with two periodicities , 6 or 3 times the random alloy < 110 > lattice parameter. The degree of or dering or domain size increases with growth temperature, as seen by increas ing definition of the superlattice fringes in the images, and by a change f rom streaks to superlattice spots in the selected area diffraction patterns . While the formation mechanism is likely a surface mediated process, no di fferences were detected for samples in compression or tension, or between t hose undoped or carbon doped. The ordering correlates with large anisotropi es of up to 150% in [110]/[11 (1) under bar] sheet resistance ratios. (C) 2 001 American Institute of Physics.