EFFECT OF GROWTH-RATE ON STEP STRUCTURE AND ORDERING IN GAINP

CuPt ordering is widely observed in GaInP epitaxial layers grown by or ganometallic vapor phase epitaxy. The formation of this spontaneously ordered structure during epitaxial growth is intimately related to the atomic-scale physical processes occurring on the surface, specificall y surface reconstruction and the attachment of atoms at steps. For gro wth on singular (001) GaAs substrates the surface structure, measured using atomic force microscopy, is seen to consist of small islands sur rounded by either monolayer or bilayer steps. An increase in the growt h rate from 0.25 to 2.0 mu m/h with a constant tertiarybutylphosphine partial pressure at 670 degrees C has no effect on either the degree o f order or the step structure. Only the step spacing is observed to ch ange. It decreases systematically as the growth rate is increased, fol lowing an approximate 1/(growth rate) (1/2) dependence. As the growth rate increase's, the time atoms have to rearrange before being frozen due to coverage by the next layer decreases. This leads directly to th e dependence observed. These observations are consistent with previous observations which appear to show a close correlation between step st ructure (monolayer versus bilayer) and ordering, although the causativ e factor has not been determined. (C) 1997 American Institute of Physi cs.